Ecology of Winyah Bay, South Carolina, and potential impacts of energy development

[From the U.S. Government Printing Office, www.gpo.gov]

U. S. DEPARTMENT OF COMMERCE NOAA
COASTAL SERVICES CENTER
2234 SOUTH HOBSON AVENUE
CHARLESTON, SC 29405-2413

ECOLOGY OF WINYAH BAY, SOUTH CAROLINA, AND POTENTIAL IMPACTS
OF ENERGY DEVELOPMENT

Edited by

Dennis M. Allen and Stephen E. Stancyk, Co-Principle Investigators
and
William K. Michener, Project Coordinator

Belle W. Baruch Institute for Marine Biology
and Coastal Research
University of South Carolina
Columbia, SC 29208
Property of CSC LibralT

A Final Report of Study Year 1
To the Coastal Energy Impact Program (NOAA)

January 1982

Funds provided by the National Oceanographic and Atmospheric Administration,
U.S. Dept. of Commerce, through the Coastal Energy Impact Program (Grant
No. NA-79-AA-D-Z-025). Awarded through the Division of Natural Resources,
Governor's Office, State of South Carolina.

This report should be cited:

Allen, D.M., S.E. Stancyk, and W.K. Michener, eds. 1982.
Ecology of Winyah Bay, SC and Potential Impacts of
Energy Development.
Baruch Institute Special Publication No. 82-1
275pp.

-C I

TABLE OF CONTENTS

LIST OF TABLES iii

LIST OF FIGURES v

PREFACE x

ACKNOWLEDGEMENTS xiv

EXECUTIVE SUMMARY xv

CHAPTER 1. DESCRIPTION OF STUDY AREA 1-1
by W.K. Michener and D.M. Allen

CHAPTER 2. METHODS AND MATERIALS 2-1
by D.M. Allen, W.K. Michener, and
B.C. Lampright

rCHA"' PTER 'aP. -MY-SICAL MEASUREMENTS AND WATER CHEMISTRY 3-1
by W.K. Michener

CHAPTER 4. PHYTOPLANKTON 4-1
by W.K. Michener

CHAPTER 5. ZOOPLANKTON 5-1
by S.E. Stancyk and T.L. Ferrell

CHAPTER 6. MOTILE EPIBENTHOS 6-1
by D.M. Allen and B.C. Lampright

CHAPTER 7. SHRIMPS, CRABS, AND FISHES 7-1
by D.M. Allen and W.K. Michener

CHAPTER 8. REPTILES, BIRDS, AND MAMMALS 8-1
by D.M. Allen and S.E. Stancyk

CHAPTER 9. WINYAH BAY: 1980-81 9-1
by S.E. Stancyk, D.M. Allen, and
W.K. Michener

CHAPTER 10. IMPACTS OF PETROLEUM ON ESTUARINE ECOSYSTEMS:
PROJECTIONS FOR WINYAH BAY 10-1
by W.K. Michener and S.E. Stancyk

LIST OF TABLES

CHAPTER I DESCRIPTION OF THE STUDY AREA PAGE

1-1 Locations, geomorphological characteristics,
and water quality classification of the
Winyah Bay sampling sites ........................1-13

CHAPTER 2 METHODS AND MATERIALS

2-1 Cruise numbers and dates for all field
collections made in NMF, SJ, and Winyah Bay .......2-2

2-2 Generalized sampling program for major
cruises at NMF and SJ Creeks ......................2-3

CHAPTER 4 PHYTOPLANKTON

4-1 Natural and man-imposed conditions which
determine levels and rates of change of
factors affecting abundance and succession
of estuarine phytoplankton ........................4-9

CHAPTER 5 ZOOPLANKTON

5-1 Relative abundance of zooplankton on major
cruises at NMF and SJ .............................5-5

CHAPTER 6 MOTILE EPIBENTHOS

6-1 Percent composition of organisms in epibenthic
sleds collections on major cruises at No Man's
Friend and South Jones Creeks .....................6-7

6-2 Mean densities of pericarid crustaceans
expressed as the number of organisms per
cubic meter of water filtered .....................6-9

6-3 Mean densities of juvenile shrimps, Lucifer
faxoni and Acetes americanus, expressed as
number of organisms per cubic meter of water
filtered .........................................6-13

CHAPTER 7 SHRIMPS, CRABS, AND FISHES

7-1 Taxonomic list of fishes collected with
all gear types from August 1980 through
July 1981 ........................................7-18

7-2 Numbers of individuals of the eight most
abundant fishes in trawl collections at
NMF and SJ on all cruises ........................7-32

7-3 Weight in grams of individuals of the eight
most abundant fishes in trawl collections at
NMF and SJ on all major cruises ..................7-33

LIST OF TABLES (CONT.)
PAGE
7-4 Diversity indiCes used for fish community
analysis .........................................7-48

7-5 Values for fish diversity indices at NMF
and SJ Creeks ....................................7-49

CHAPTER 8 REPTILES, BIRDS, AND MAMMALS

8-1 Checklist of birds known to use Mud Bay
and surrounding creeks and marshes ................8-7

CHAPTER 9 WINYAH BAY: 1980-81 CRUISES

9-1 Physical and chemical characteristics of
water samples collected in Winyah Bay,
South Carolina during August 1980
through July 1981 .................................9-3

9-2 Relative abundance of zooplankton on major
cruises in Winyah Bay .............................9-6

9-3 Abundance of zooplankton common species in
Winyah Bay, S.C ...................................9-7

9-4 Dominant organism at each station on
each cruise ...................................... 9-16

9-5 Mean number of mysids, amphipods, shrimp
larvae, fish larvae and total organisms per
cubic meter for the Winyah Bay cruises from
August 1980 through July 1981 ....................9-17

LIST OF FIGURES

CHAPTER I DESCRIPTION OF THE STUDY AREA PAGE

1-1 Map of Mud Bay section of Winyah Bay
showing sampling sites at No Man's
Friend and South Jones Creeks .....................1-2

1-2 Mean air temperature for all cruises
at NMF and SJ Creeks ..............................1-8

1-3 Mean surface water temperature for
all cruises at NMF and SJ Creeks ..................1-9

1-4 Map of Winyah Bay estuary showing
sampling locations ...............................1-10

CHAPTER 2 METHODS AND MATERIALS

2-1 Generalized designs for nets used to
collect microscopic animals .......................2-6

2-2 Generalized form of semi-balloon otter
trawl used to collect macroinvertebrates
and fishes .........................................2-9

CHAPTER 3 PHYSICAL MEASUREMENTS AND WATER CHEMISTRY

3-1 Mean air temperatures for all cruises at
NMF and SJ Creeks .................................3-2

3-2 Mean surface and bottom water temperatures
at NMF and SJ Creeks ..............................3-3

3-3 Mean surface and bottom salinities at NMF
and SJ Creeks .....................................3-6

3-4 Mean secchi disk visibilities at NMF and
SJ Creeks .........................................3-8

3-5 Mean surface and bottom concentrations
of total nitrogen at NMF and SJ Creeks ...........3-11

3-6 Mean surface and bottom concentrations
of (nitrate and nitrite) nitrogen at
NMF and SJ Creeks ................................3-12

3-7 Mean surface and bottom concentrations of
total phosphorus at NMF and SJ Creeks ............3-16

3-8 Mean surface and bottom concentrations of
orthophosphate-phosphorus at NMF and SJ
Creeks ...........................................3-17

CHAPTER 4 PHYTOPLANKTON

4-1 Mean surface and bottom conentrations of
chlorophyll a at NMF and SJ Creeks ................4-7

LIST OF FIGURES (CONT.)
PAGE
4-2 Mean surface and bottom concentrations of
phaeo-pigments at NMF and SJ Creeks ..............4-11

CHAPTER 5 ZOOPLANKTON

5-1 Holoplankton of Winyah Bay, S.C ...................5-7

5-2 Meroplankton in Winyah Bay, S.C ..................5-12

5-3 Mean densities of adult and copepodid
Acartia tonsa on cruises 1-18 at NMF
and SJ .......................................... 5-17

5-4 Mean densities of Parvocalanus
crassirostris on cruises 1-18 at NMF
and SJ ........................................... 5-20

5-5 Mean densities of Pseudodiaptomus
coronatus on cruises 1-18 at NMF and SJ ..........5-22

5-6 Mean densities of Centropages hamatus on
cruises 1-18 at NMF and SJ ........................ 5-24

5-7 Mean densities of Oithona colcarva on
cruises 1-18 at NMF and SJ .......................5-26

5-8 Mean densities of Euterpina acutifrons
on cruises 1-18 at NMF and SJ ....................5-27

5-9 Mean densities of chaetognaths in
zooplankton collections on cruises
1-18 at NMF and SJ ...............................5-29

5-10 Mean densities of chaetognaths in
epibenthic sled collections on
cruises 1-18 at NMF and SJ .......................5-30

5-11 Mean densities of appendicularians
on cruises 1-18 at NMF and SJ ....................5-32

5-12 Mean densities of barnacle nauplii
on cruises 1-18 at NMF and SJ ....................5-35

5-13 Mean densities of barnacle cyprids
on cruises 1-18 at NMF and SJ ....................5-36

5-14 Mean densities of crab zoeae on
cruises 1-18 at NMF and SJ .......................5-38

5-15 Mean densities of bivalve larvae on
cruises 1-18 at NMF and SJ .......................5-40

5-16 Mean densities of gastropod veligers on
cruises 1-18 at NMF and SJ .......................5-41

LIST OF FIGURES (CONT.)

CHAPTER 6 MOTILE EPIBENTHOS PAGE

6-1 Pericaridan Crustacean diagrams ...................6-3

6-2 Mean densities of mysid shrimps in
epibenthic sled collections on cruises
1-18 at NMF and SJ ................................6-5

6-3 Decapod Crustacean diagrams ......................6-12

6-4 Mean densities of shrimp larvae in
epibenthic sled collections on
cruises 1-18 at NMF and SJ .......................6-16

6-5 Mean densities of total shrimp in
epibenthic sled collection on
cruises 1-18 at NMF and SJ .......................6-18

6-6 Diagrams: crab megalopa, stomatopod larva,
sciaenid fish larva, anchovy larva ...............6-21

6-7 Mean densities of crab megalopae in
zooplankton collections on cruises
1-18 at NMF and SJ ...............................6-22

6-8 Mean densities of crab megalopae in
epibenthic sled collections on cruises
1-18 at NMF and SJ ...............................6-23

6-9 Mean densities of fish larvae in
epibenthic sled collections on cruises
1-18 at NMF and SJ ...............................6-29

6-10 Mean densities of total organisms in
epibenthic sled collections on cruises
1-18 at NMF and SJ ...............................6-31

CHAPTER 7 SHRIMPS, CRABS, AND FISHES

7-1 Total numbers of adult penaeid shrimps
in trawl collections on major cruises .............7-4

7-2 Length frequency analysis of white
shrimps in trawl collections on major
cruises at NMF and SJ .............................7-5

7-3 Total weight of adult penaeid shrimps in
trawl collections on major cruises ................7-6

7-4 Length frequency analysis of brown shrimps
in trawl collections on major cruises at
NMF and SJ ........................................7-9

vii

LIST OF FIGURES (CONT.)
PAGE
7-5 Length frequency analysis of blue crabs in
trawl collections on major cruises at NMF
and SJ ...........................................7-14

7-6 Length frequency analysis of spot in trawl
collections on major cruises at NMF and SJ .......7-36

7-7 Length frequency analysis of Atlantic
croaker in trawl collections on major
cruises at NMF and SJ ............................7-38

7-8 Total numbers of all fishes in trawl
collections on major cruises .....................7-45

7-9 Total weights of all fishes in trawl
collections on major cruises .....................7-47

viii

PREFACE

An estuary is defined as a semienclosed coastal basin in which fresh-

� ~~water runoff is mixed with seawater. Superimposed on the pattern of tidal

movements of water toward and from the ocean is the discharge of freshwater

I ~~~into the estuary from terrestrial sources. The result is a physically com-

plex environment. At any location within an estuary, tidal amplitude, cur-

rent direction and velocity, temperature, salinity, turbidity, nutrient
concentrations and many other physical and chemical properties of the water

column change over time. Relatively large lateral and vertical fluctuations

I ~~~in environmental parameters occur on tidal, diurnal, and seasonal time
scales.

Estuarine organisms are more tolerant of large and irregular fluctua-

j ~~~tions in environmental factors than freshwater and open ocean organisms.

Few species are adapted to live under such stressful conditions and, typi-

cally, estuaries are populated by high densities of relatively low numbers

� ~~~of species. One species of grass, Spartirta alternif'lorap completely domin-

ates high salinity estuarine marshes from the maritime provinces of Canada

3 ~~~to northern Florida. Because of the abundance and photosynthetic capa-

bilities of this plant, Spartina marshes are among the most productive

I ~~~ecosystems on Earth. Benthic algae and phytoplankton also contribute to

j ~~~to the high productivity of estuaries.

I ~~~~~~~~~~~~~iX

Estuarine animals are dependent on the production of proteins, sugars,

and other organic materials by plants; however, the majority of invertebratesI

do not feed directly on green plants. Decomposing marsh grasses and otherI

vegetation (detritus) form the basis of the food web in estuaries. Filter

feeders such as oysters, clams and planktonic crustaceans, derive their3

energy from microscopic organic particles and phytoplankton. Scavengers

such as shrimp or crabs consume larger detrital particles which accumulate1

On the bottom. Many predators, especially fishes, inhabit estuaries, and5

most have generalized diets which enable them to consume whatever prey

items are available. The estuarine food web is complex and, although

estuarine ecologists have learned a great deal in the last decade, much

more research is needed before the interactions between various types of

Organisms are understood.I

One aspect of estuaries that has great implications for society is

the production of commercially valuable populations of shrimps, crabs and

fishes. Some of these species complete their entire life cycles withinI

the estuaries, but the adults of most species live and reproduce in the

ocean. Larval shrimps and fishes migrate into estuarine areas where abun-5

dant food supplies are available. The significance of estuaries as nursery

areas cannot be overemphasized, and there is little doubt that withoutI

healthy estuaries, the commercial fisheries would disappear.

Winyah Bay is not only one of the largest estuaries in the southeast,

it has some characteristics which make it unique. Few other estuaries are

almost completely bordered by marshes. No other estuary is surrounded with

so much land that has been set aside, in perpetuity, for the purpose of

research, education and conservation (The Belle W. Baruch Foundation's

X~~~~~~~

Hobcaw Barony and the Thomas Yawkey Wildlife Center). Few other estuaries

I ~~~have such large populations of endangered or threatened species (.e.g. short-

I ~~~nose sturgeon, brown pelican, bald eagle, sea turtles).

The vast size and dynamic nature of Winyah Bay renders any comprehen-

sive ecological investigation of physical, chemical, and biological charac-
teristics of the estuary an impossible task. Our two-year study of the

ecology and potential impact of petroleum on the estuary was designed to

I ~~~provide basic ecological information which would constitute a framework

from which potential impacts could be predicted. This report summarizes
I ~ ~~the results of the first year of that study.

I ~~~~The initial field study concentrated on the two major creeks which

g ~~~exchange water and materials between the Mud Bay section of Winyah Bay and

the North Inlet salt marsh. The sampling program consisted of nine inten-

j ~~~sive 24-hour cruises at No Man's Friend and South Jones Creeks every six

weeks, plus an additional nine shorter cruises between the major cruises.

I ~~~Nine Winyah Bay cruises in the first year provided information from six

stations located between the ocean and freshwater extremes of the estuary.

Hundreds of hours of field measurements and collections and thousands of

5 ~~~hours of laboratory and computer analysis have resulted in a massive data

base and an initial understanding of the basic ecological processes of the

I ~~~system.

I ~~~~The data presented in this volume represent only the first level of

analysis. Seasonal trends are essential to the characterization of any

I ~~~ecosystem, and temporal variations on this level are described and discussed

3 ~~~with respect to the various locations sampled in Winyah Bay. Short term

(daily and hourly) variations in the physical characteristics, chemistry,

5 ~~~~~~~~~~~~~~xi

and abundance of organisms represent a more specific level of information3

about estuarine dynamics. These tidal and diel fluctuations will be the

Subject of several manuscripts which will be published in the scientific

literature at a later date.

A one year study of any ecosystem, especially one as complex as an

estuary, provides only a passing glimpse of a long-lived and very dynamic3

entity. Annual fluctuations in freshwater input, for instance, could

radically change the character of the locations which were sampled the
previous year. Nevertheless, the information gathered in this study has5

filled a tremendous void. Data from No Man's Friend and South Jones Creeks

will become part of another even larger effort by the Belle W. Baruch5

Institute of the University of South Carolina to document and analyze long-

term changes in the North Inlet salt marsh. An understanding of natural

fluctuations and long-term trends in an undisturbed ecosystem such as Northj

Inlet is essential if scientists are going to be able to predict the effects

of natural and man-induced perturbations on such ecosystems.I

Studies during the second year are focused on the six original Winyah3

Bay stations plus five additional ones. This network of sampling sites

represents each of the major subtidal habitat types within the estuary.3

Emphasis has been placed on the early life stages (eggs, larvae, and young)

of crustaceans, especially shrimps and crabs, and fishes. Spatial and

temporal variations in abundance will be correlated with measurements of the3

physical and chemical characteristics to provide information on the utiliz-

ation of the estuary by young organisms. The susceptibility and vulnerabil-1

ity of larval stages to petroelum pollution in Winyah Bay will be discussed

in light of these studies.

xiiI

This report has been written for scientific accuracy, but in a style

I ~~~which, hopefully, can be useful to non-scientists. A description of the

5 ~~~study area and methods is followed by chapters which discuss each of the

major sets of measurements that were taken. Another chapter summarizes

3 ~~~the data from the first year cruises in Winyah Bay. The potential impacts

of energy related industry, especially petroleum, are discussed in the

I ~~~final chapter. Over the last decade the enormous amount of money and time

5 ~~~spent by governments and industries of the world on studies of the effects

of oil in aquatic ecosystems has resulted in thousands of documents. It

3 ~~~is beyond the scope of this project to review all of this literature;

however, our assessment of the potential impact of oil in Winyah Bay
estuary is based on our first-hand knowledge of estuarine ecology and
opinions generated from the reading of hundreds of scientific studies con-

ducted in similar ecosystems. We believe this assessment constitutes an

j ~~~initial attempt toward understanding the fundamental problems associated

with the acute and chronic pollution of an estuary by petroleum.

~~~~~~~~~~~~~xii

ACKNOWLEDGEMENTS

The editors acknowledge the contribution of time, effort, and mater-
ials from many persons, especially full time research specialists T. Lance
Ferrell and Bruce C. Lampright, who assisted in all aspects of the study
and were especially diligent in their tedious task of processing zooplank-
ton and epibenthic sled collections. Carol Schmidt and Douglas Baughman
are thanked for providing much needed assistance during intensive field
sampling periods.

Additional field and laboratory assistance was provided by W. Allen,
L. Barker, R. Christy, S. Hutchinson, W. Johnson, and R. Talbert. D. Caton
and P. Johnson are thanked for keeping the field sampling equipment in
operating condition.

Special thanks are given to Avis Hutchinson for her patience and
expertise in the typing of all drafts of the report. Betsy Haskin is
commended for the excellent production of all maps and figures. Robyn
Lampright typed much of the manuscript and provided help in illustration,
and Betty Mitchell typed references and revisions.

Dr. F.J. Vernberg, Director of the Belle W. Baruch Institute for
Marine Biology and Coastal Research, University of South Carolina, and
his staff, especially Mrs. Virginia Smith, are thanked for providing
facilities and resources for the study as well as editorial and other
logistic aid.

This study was funded by the National Oceanographic and Atmospheric
Administration, U.S. Dept. of Commerce, through the Coastal Energy Impact
Program (grant no. NA-79-AA-D-Z-025). The grant was awarded through the
Division of Natural Resources, Governor's Office, State of South Carolina.

xiv

3 ~~~~~~~~~EXECUTIVE SUMMARY

1. We conducted an intensive study of the physical, chemical, and
biological characteristics of Winyah Bay, especially those creeks
which exchange water and materials with North Inlet. The results of
these studies are discussed with respect to the potential effects of
energy related development in the estuary.
2. Phytoplankton production was highest from June through Septem-
ber when water temperatures were high, vertical visibility in the
I ~ ~~~water column was low, concentrations of total nitrogen and total
phosphorous were at their highest levels, and concentrations of ni-
trate-nitrite and orthophosphate were at low levels. High chloro-
I ~ ~~~phyll a and phaeopigment concentrations during summer indicated max-
imum production and turnover rates for the year occur during the warm
months. Phytoplankton populations would be expected to experience
initial adverse impacts after exposure to spilled oil. Recovery to
near normal levels would be expected after toxic soluble fractions
were dispersed.
1 ~~~3. Rooted marsh plant populations which almost completely surround
Winyah Bay would probably be severely impacted by an oil spill.
Hundreds of acres of Spartina marsh could be eliminated by a spill.
I ~ ~~~Recovery would be very slow because of the inhibition of seed germi-
nation and the persistance of oil in marsh muds for at least a de-
cade. Marsh grasses exposed to constant low level discharges of oil
3 ~~~~and grease from refinery effluents would be adversely effected.
4. Zooplankton composition and abundance in Winyah Bay was similar
to other Southeast coastal systems. Permanent members of this di-
I ~ ~~~verse microscopic community were mostly herbivorous copepods. Tem-
porary members of the zooplankton included eggs and larvae of most
crabs, shrimps, shellfishes, fishes, and many less familiar inver-
tebrates. Diversity and abundance was highest in summer for most
species, especially larvae. Acute poisoning from an oil spill would
destroy sensitive early life stages and could eliminate a single
year's reproductive effort by commercially important crustacean, mol-
lusc, or fish populations. Copepods would probably repopulate the
area rapidly. Long term exposure to low concentrations of oily resi-
dues and effluents could have more subtle sublethal effects on some
organisms.
5. Mysid shrimps, amphipods, and other less familiar small crusta-
I ~ ~~~ceans, which constitute major food sources for juvenile fishes, live
near or on the bottom and are permanent members of the motile epiben-
thos. Most late larval and juvenile crabs, shrimps, and fishes also
live close to the bottom of marsh creeks and estuarine areas. Since
I ~ ~~~non-soluble oil droplets adhere to suspended sediments and accumulate
on the bottom, the potential impact of an oil spill or chronic dis-
charges of petroleum compounds on animal populations which live, feed
and reproduce near the bottom is likely to be serious. Damage to
permanent and temporary members of the motile epifauna would affect

the entire estuarine food web. Non-motile benthic communities are1
particularly susceptible to damage by polluted sediments.
6. Adult shrimps, crabs, and fishes constitute major commercial and1
recreational resources in Winyah Bay. Larval stages are usually most
sensitive to oil pollution; however, polluted estuarine areas could
inhibit migration patterns, feeding, growth, reproduction and otherI
activities of juveniles and adults. Long-term effects of oil pol-
lution on these populations may result in lower availability, and
seafood may become tainted and contain compounds carcinogenic to man.
7. Winyah Bay and its surrounding wetlands support some of the high-
est densities of nesting wading birds and migrating waterfowl in the
region. Endangered and threatened bird, reptile, fish, and mammalI
populations presently inhabit the estuary. All are susceptible to
acute and chronic oil pollution.5
S. Winyah Say, one of the largest estuaries in the Southeast, ex-
changes water and materials with pristine North Inlet, site of one
of the world's most active estuarine research programs, and with the
Santee system, which is about to be radically altered by rediversion.
We are lacking information on the extent to which Winyah Bay Estuary
is already stressed by industrial, agricultural, and domestic inputs.
The inevitable degradation of water quality associated with an oilI
refinery would have negative local, regional and national repercussions.

Xv~~~~~~i

CHAPTER 1. DESCRIPTION OF THE STUDY AREA

No Man's Friend Creek (NMF) and South Jones Creek (SJ) are relative-

ly shallow marsh waterways which connect two hydrographically distinct

estuarine ecosystems (Fig. 1-1). Haulover Creek is the only other water-

way connecting Winyah Bay and North Inlet, but it is so narrow and shallow

that water flow is restricted to within a few hours of high tide.

The creeks meander through marshes which are dominated by saltmarsh

cordgrass (Spartina alterniflora). Areas of the marsh surface which are

slightly higher in elevation with respect to high tide are vegetated by

big cordgrass (Spartina cynosuroides) and black needle rush (Juncus

roemerianus). High marsh flats and edges are characterized by saltmeadow

hay (Spartina patens), several species of glass worts (SaZicornia spp.),

salt grass (Distichlis spicata), sea oxeye (Borrichia frutescens) and sea

lavender (Limonium carolinianum). A transitional shrub community com-

posed of marsh elder (Iva frutescens) and southern red cedar (Juniperus

siZicola) border portions of SJ, especially near Collins Island. A mari-

time forest dominated by loblolly pine (Pinus taedo) and live oak (Quercus

virginiana) is located on the island.

With the exception of the several hundred meter interface of SJ and

Collins Island, the creeks are bordered by steep marsh banks. Only nar-

row muddy intertidal slopes fringe the marsh banks. More extensive in-

Hobcaw Barony

Oyster Bay
NoMans Friend .T.

.: . .~ � I:';

North Isand

South Jones Ocean 1

N I9�3

Figure 1-1. Map of Mud Bay section of Winyah Bay showing sampling sites at
No Man's Friend and South Jones Creeks. The dark circles indi-
cate the stationary measurements and water sample collection
stations. The hatched zones indicate the area in which all net
collections were made.

1 o I

tertidal mudflats are located at the intersection of NMF and Mud Bay;

large flats also occur at the mouths of SJ and Sign Creeks.

The subtidal substrate at NMF consists of a layer of fine organic

sediments over a more firm muddy-sand base. Subtidal populations of

macroalgae, especially sea lettuce (Ulva Zactuca), occur from November

through May. Sponges, gorgonians (soft corals), and other sessile ben-

thic organisms characteristic of nearby creek bottoms in North Inlet do

not occur in NMF. Only small and isolated clusters of low intertidal

oysters (Crassostrea virginica) were observed. Preliminary bucket

dredge tows and S.C.U.B.A. collected benthic box cores indicated that a

low diversity of macroinvertebrates occurred in NMF. The soft clam

(Macoma baltica) was the most conspicuous bivalve mollusc and few large

polychaetes were found.

Although the sediment character of SJ and NMF is similar, the

bathymetry of the two creeks is very different. On the North Inlet side

of the South Jones Creek sampling platform, intertidal oyster bars border

the creek banks and form islands which are surrounded by soft mud sedi-

ments at low tide. The platform is situated in a basin at the converqence

of South Jones and Sign Creeks (Fig. 1-1). The creek bottom in SJ and

Sign Creeks between the basin and Winyah Bay is muddy sand. Generally,

the bottom topography is more irregular at SJ than NMF and larger accumu-

lations of root masses, Spartina stalks, and tree branches occur at SJ.

Vascular plant detritus (decomposing plant material) was usually more

abundant in net collections at SJ. No sponges and gorgonians were collected,

but fairly well developed subtidal oyster populations were found. Benthic

macroalgae and fouling epibenthic organisms (e.g. bryozoans, barnacles,

1-3

hydroids) were more abundant in SJ than NMF. Detailed benthic studies

were not conducted, but preliminary dredgings and dives indicated that

the benthic infauna was similar to that collected in NMF.

The physical, chemical and biological characteristics of NMF and SJ

Creeks are influenced by tidal exchange between North Inlet and Winyah

Bay. Kjerfve (1978) estimated that 80% of the exchange between the two

systems occurs through SJ. The relationship between connecting creeks

and adjacent estuaries has been examined at SJ and other similar systems

(Pritchard, 1960; Pritchard and Gardner, 1974; Bowman, 1976; Van de Kreeke,

1978).

North Inlet salt marsh is one of the most intensively studied salt

marsh ecosystems in the world. It is a bar-built class C type estuary

(Pritchard, 1955), which exchanges coastal waters through a wide and

shallow inlet. Hydrographic characteristics include a salinity ranae of

30-34 parts per thousand (o/oo), average channel depth of 5 m, and a semi-

diurnal tide with a maximum spring range of 2.5 m and a neap range of

approximately 1.0 m (Kjerfe, 1978). Water quality in North Inlet is

excellent and shellfish harvesting is approved (South Carolina Department

of Health and Environmental Control, 1977; South Carolina Pollution Con-

trol Authority, 1972). Annual freshwater input into the North Inlet marsh

is low because of the relatively small drainage basin (T. Williams, Baruch

Forest Science Institute, personal communication).

The hydrographic characterization of NMF and SJ conducted in this

study was based on hourly measurements of salinity, temperature and depth.

Details of these physical measurements are given in Chapters 2 and 3.

1-4

3Hydrographic data was collected from a stationary boat at SJ adjacent to

Sign Creek (33016'53"N, 79o11'32"W) and in midchannel at NMF near Mud Bay

(33o18'12"N, 79011'32"W) (Fig. 1-1).

Ten complete ebb tides were observed in NMF. The ebb tide lasted an

average of 6.9 hours (5-9 hours). The direction of the ebb tide was ini-

tially toward Winyah Bay for 2-5 hours (mean=3.8 hours). During this

period, surface salinity increased and bottom salinity increased or re-

mained unchanged. Salinity of surface water was less than or equal to

bottom salinity. At the conclusion of the Winyah Bay directed ebb tide,

large portions of Mud Bay were exposed and only minimal surface flow

occurred. The direction of the remainder of the ebb tide was toward North

Inlet and lasted 2-4 hours (mean=3.1 hours). During this period, surface

salinity typically decreased or remained stable. Recorded surface salini-

ties were less than or equal to bottom salinities.

Eight of the thirteen flood tides observed at NMF were directed to-

ward North Inlet. The flooding tide toward North Inlet lasted an average

of 4.6 hours (3-6 hours). Surface salinity usually decreased or remained

unchanged and bottom salinity always decreased or remained unchanged. Sur-

face salinities were less than or equal to bottom salinities.

The five flooding tides directed toward Winyah Bay averaged 5.0 hours

in length (4-7 hours). Surface salinity always increased and bottom salin-

ity increased or remained unchanged. Recorded surface salinities were less

than or equal to bottom salinities.

The direction of the floodina tide at NMF appeared to be related to

tidal amplitude. During periods of tidal flooding toward Winyah Bay,

tidal amplitude averaged 1.46 m and varied from 1.2 m to 1.7 m. Tidal

amplitudes were much greater during periods of tidal flooding toward

North Inlet, averaging 1.86 m with a range of 1.4 m to 2.1 m. Only two

instances were observed in which tidal amplitude was low (1.4 m) and

tidal flooding was directed toward North Inlet. In both cases, strong

southwesterly (or south-southwesterly) winds prevailed and wind speeds

averaged 5.8 mph or 11.5 mph. Generally, unless complicated by strong

southerly winds, flooding at NMF was directed toward Winyah Bay during

periods when tidal amplitudes were low (<1.75 m) and toward North Inlet

when tidal amplitudes were high (>1.75 m).

Thirteen complete ebb tides were studied at SJ. Ebb tides averaged

5.5 hours (4-7 hours). All ebb tides were directed toward Winyah Bay.

During the ebb tide, surface salinity either increased (7 times) or de-

creased (6 times); no definite pattern was noted. However, it was obser-

ved on numerous occasions that surface water entered SJ from Sign Creek.

The influx of large quantities of less saline water from Sign Creek may

have been responsible for the lower surface salinity at SJ. Unfortunately,

attempts to quantify input of fresher water from Sign Creek were unsuccess-

ful due to the relatively high current velocity threshold of available

current meters and a shortage of time and manpower. Bottom salinity at

SJ during ebb tides usually decreased or remained unchanged.

Twelve complete flood cycles were monitored at SJ. The average length

of flood tides was 6.2 hours (5-9 hours). All flood tides were directed

toward North Inlet. Surface and bottom salinities usually decreased dur-

ing the flooding period. Surface salinities Generally remained lower than

bottom salinities (9 times) throughout the flood tide. On three occasions,

1-6

surface salinity was not substantially different from bottom salinity.

Hydrographical data obtained from SJ substantiate the claim that a perma-

nent nodal point, which limits exchange between North Inlet and Winyah

Bay, exists in upper Jones Creek (Schwing and Kjerfve, 1980),

Average air and surface water temperatures during the year (Fig. 1-2

and 1-3) followed a similar pattern for NMF and SJ: decreasing from sum-

mer maxima from July through September to minima in January, then steadily

increasing from February through June. Highest average surface water tem-

peratures were recorded in July at NMF (31.46�C) and SJ (32.95�C). Lowest

average surface water temperatures were recorded in January at NMF (3.75�C)

and SJ (3.80�C). The highest average air temperatures were observed in

August at NMF (28.90�C) and September at SJ (29.81�C). Lowest average air

temperatures were recorded in January at NMF (8.50�C) and SJ (7.42�C). A

more complete analysis of the physical and chemical characteristics of the

creeks appears in Chapter 3.

Winyah Bay (Fig. 1-4) is a class B type estuary according to Pritch-

ard's (1955) classification. The estuary has a mean depth of 4.2 m and a

mean tidal amplitude of 1.0 m (1.2 m spring tides). Some of the freshwater

input emanates from a 16,340 square mile watershed which drain swamps and

marshes in northeastern South Carolina and southeastern North Carolina.

This drainage arrives at the headwaters of Winyah Bay through the Great

Pee Dee and Little Pee Dee Rivers which merge with the Waccamaw River just

north of the city of Georgetown. The Black River drains another major

watershed. The Sampit River drains a relatively small area of approximate-

ly 240 sq. miles (The Conservation Foundation, 1980).

Winyah Bay's widest dimension is in the center of the estuary (4.5

miles) and narrowest at the ocean entrance (0.75 miles). The width is

1-7

30 -

0
o 20- g
L.
n~~~~~~~~~

O-

Cruise I 3 5 7 9 I11 13 15 17

Month A S S 0 N N D J J F M M A M J J J A

Figure 1-2. Mean air temperature for all cruises at NMF (.dark circle) and SJ (.open circle) Creeks.
Vertical lines through the circles represent plus or minus the standard error.

_ m ruit _ 3 5 7 _ _ _ _ __
~~~ ~~~~~ mm m m -lie rm ! m

28.8 - /

0
CD~~~~~~~~~~~~~~~~~~~~~~~~,
0

. . i

k.Vta) n
Ci I
,- !
C-

~, 9.6-
o~~~~~~~

Cruise I 3 5 7 9 I I 13 15 I7

Month A S S O N N DJ J F M M A M J J J A

Figure 1-3. Mean surface water temperature for all cruises at NMF (dark circle) and SJ (open circle)
Creeks. Vertical lines through the circles represent plus or minus the standard error.

Black and Pee DeeRi accamaw

fWR ~ W :Debidue
Georgetown . .1/ Island

Sampit Ri ' ',.

r g<~BW Baruch. I'
WNYAH North Inlet
BAY

11 . I.
7 North

Eslthrvaile I Si

i fMB

ATLANTIC
Yawkey Wildlife OCEAN
~~~Center OCEAN

33�105
Annandale
Plantalion : MN

A *

North Inlet I
Area

AJIOLINA *North Santee km I
Inlet 70710'

Figure 1-4. Map of Winyah Bay Estuary showing sampling locations at: Sampit
River (SR), Pee Dee River (PD), Waccamaw River (WR), Esterville
Plantation (EP), Mud Bay (MB), South Jones Creek (SJ), No Man's
Friend Creek (NMF), and Mother Norton Shoal (MN).

1-10

about 1.3 miles in the upper bay where the rivers converge with the basin.

Clay-rich sediments dominate the bottom in the upper bay and sand-rich

substrates characterize the area near the ocean (Colquhoun, 1973). Few

studies have examined hydrographic properties of Winyah Bay (Johnson, 1972;

Mathews and Shealy, 1978; Trawle and Boland, 1979).

Winyah Bay is almost completely surrounded by marshes. More than

12,740 hectares (31,823 acres) of coastal marshes are associated with the

system; approximately 87% of these marshes are influenced by the tides.

Salt marshes (s. alterniflora) are confined to the lower bay. Brackish

marshes (s. cynosuroides) comprise about 18% of Winyah Bay's wetlands

(Tiner, 1977).

Water quality in Winyah Bay is primarily influenced by inputs from the

Georgetown area. Georgetown is one of the most extensively developed areas

of the Sea Island Coastal Region (Mathews et al., 1980). Winyah Bay has

been classified as "SC" (lowest water quality classification), meaning that

its waters are suitable for crabbing, commercial fishing and for the sur-

vival and propagation of marine flora and fauna (South Carolina Department

of Health and Environmental Control, 1977; and South Carolina Pollution

Control Authority, 1972). Shellfishing in Winyah Bay has been restricted

since 1964 (U.S. Department of Commerce, 1979).

The Sampit River is the most heavily polluted river in the Winyah Bay

system, receiving discharges from, among other sources, waste treatment

plants, a pulp mill, and a steel mill. The Sampit River has high levels

or organic pollutants and is ranked "SC", the lowest quality category used

by the state (South Carolina Department of Health and Environmental Control,

1977; South Carolina Pollution Control Authority, 1972). Shellfishing has

been prohibited in the Sampit River since 1964 (U.S. Department of

Commerce, 1979). Pollution of the Pee Dee, Waccamaw and Black Rivers is

dominated by agricultural runoff (Mathews et al., 1980).

Precise locations and characteristics (water quality, salinity ranqe,

and geomorphology) of the six sampling sites in Winyah Bay are summarized

in Table 1-1. The Sampit River sampling site was located near the South

Carolina State Ports Authority Terminal. Sampit River is a coastal river,

originating in the coastal plain, and flow dominated by tidal actions

(Mathews et al., 1980). The Sampit River was the smallest river sampled

and exhibited the highest salinity regime.

The Pee Dee and Waccamaw Rivers supply most of the freshwater input

to Winyah Bay. The area sampled in the Pee Dee River was approximately

1.25 km north of the bridge, located near mid-channel, and characterized

by shallow depths and slow water velocities. Zooplankton and epibenthic

sled samples from the Pee Dee River contained the heaviest detrital loads

of any Winyah Bay sampling sites. The lowest range in salinities was

obtained from the Pee Dee River. The Waccamaw River station was located

mid channel approximately 1.25 Km north of Highway 17 bridge. The Wacca-

maw River was the widest and deepest river sampled. Salinities were the

lowest recorded and water quality classification was highest.

The Esterville Plantation site was located near the middle of the

Western Channel approximately I km north of the Intracoastal Waterway.

Esterville Plantation had the greatest range in salinity and heavy detri-

tus concentrations were common.

The Mud Bay location was near the lower end of Mud Bay, midway be-

1-12

Table 1-1. Locations, geomorphological characteristics, and water quality classification of the Winyah
Bay sampling sites.
(a.) (b.) (c.)
Station Location Approx. depth(m) Sediment Salinity Water quality
(Lat.-Long.) at MLW characteristics range(o/oo) classification

Sampit River 33�21'28"N 7.0 Soft mud 2.2-17.3 SC
79017'10"W

Pee Dee River 33�22'29"N 3.0 Firm mud 2.9-10.5 B
79u15'40"W

Waccamaw River 33022'30"N 8.0 Firm mud 0.0-7.8 A
79�14'45"W

Esterville Plantation 33�16'7"N 5.4 Sandy mud 10.3-30.6 SC
79016'17"W

Mud Bay 33�15'28"N 3.9 Muddy sand 11.9-31.7 SC
79013'10"W and shell

Mother Norton 33012'6"N 3.6 Sand and 27.2-35.2 SC
79011' 17"W shell

(a.) Data obtained from benthic dredge samples
(b.) Data summarized from Chapter 10
(c.) Classification scheme:
A - suitable for direct water contact use
B - suitable for domestic supply after conventional treatment, suitable also for fish propagation,
industrial and agricultural uses requiring water of lesser quality
SC - suitable for crabbing, commercial fishing, and for the survival and propagation of marine
fauna and flora (lowest water quality classification)
(Adapted from South Carolina Department of Health and Environmental Control (1977) and South
Carolina Pollution Control Authority (1972) as summarized by the Conservation Foundation (1980).

tween the main shipping channel and the spoil islands. The Mother1
Norton sampling site was located approximately 400 m from Mother Norton
Shoal and was characterized by high current velocities, bottom sediments1
of sand and shell, and a narrow high range of salinities.5

Other characteristics of the Winyah Bay sampling sites are dis-
cussed in Chapter 9.

1-14~~~~~

CHAPTER 2. METHODS AND MATERIALS

I ~~~~The primary sampling program for NMF and SJ Creeks consisted of a

3 ~~~series of nine cruises which were conducted approximately every six weeks

from August 1980 through July 1981. On the third week between the six

5 ~~~week cruises, another set of samples was collected to provide a more com-

plete record of physical, chemical, and biological characteristics of the

I ~~~Creeks. A schedule of cruise numbers and dates for the "major" intensive

six week and alternate "mini" cruises at NMF and SJ is listed in Table 2-1.

Cruise numbers and dates for the Winyah Bay collections which were done

3 ~~~during the major sample weeks are also listed.

The major cruises began early on Monday mornings when a minimum of

six persons transported equipment to the remote sampling station at NM.F.

3 ~~~Sampling commenced at 10 AM according to the outline in Table 2-2 and con-

tinued until the last collections were made at 10 AM on Tuesday. Three

I ~~~persons were usually on each of two shifts. On Wednesday morning the

5 ~~~field team moved all equipment to SJ creek where the identical sampling

schedule was carried out. On Friday of the same week, the field personnel

I ~~~collected samples at six stations from lower Winyah Bay to the river.

5 ~~~~During the major samples, physical measurements were taken every hour.

Water depth, vertical visibility (secchi disk), and current direction were

3 ~~~recorded. Water temperature and salinity were measured at 30 cm below

the surface and 30 cm above the bottom with an induction salinometer

1 ~~~~~~~~~~~~2-1

Table 2-1. Cruise numbers and dates for all field collections made in
NMF, SJ, and Winyah Bay. Odd numbered cruises are 24-hour
major samplings at the creeks and 8-hour samplings in Winyah
Bay. Even numbered cruises are mini samplings in the creeks.

LOCATIONS
CRUISE NO. DATES NMF SJ WB

1 August 11-15, 1980 X X X

2 September 3 X X

3 September 22-26 X X X

4 October 13 X X

5 November 3-7 X X X

6 November 24 X X

7 December 15-19 X X X

8 January 6, 1981 X X

9 January 26-29 X X

February 3 X

10 February 16 X X

11 March 9-12 X X

March 6 X

12 March 31 X X

13 April 20-24 X X X

14 May 11 X X

15 June 1-5 X X X

16 June 22 X X

17 July 13-17 X X X

18 August 3 X X

2-2

Table 2-2. Generalized sampling program for major cruises at NMF and
SJ Creeks. Period indicates the frequency at which each
activity was conducted over the 24-hour cruise.

PERIOD ACTIVITY

1 hr Physical measurements of water column and air

2 hr Water sample collection for nutrients and plant pigments

Zooplankton net tows, 2 replicates

Epibenthic sled tows, 3 replicates

3 hr Gill net inspection

6 hr Trawl collection

2-3

(Beckman RS5-3). Meteorological conditions including air temperature and

wind speed and direction were also measured every hour. This same set of

measurements was taken during the "mini" creek and Winyah Bay cruises.

Water samples were collected bi-hourly at the same depths as the

temperature and salinity measurements. Bottom water samples were collected

by means of a portable hand operated bilge pump with an intake hose which

was suspended 30 cm from the bottom by a weighted metal frame. A 3 ml

unfiltered sample was pipetted into pre-washed culture tubes. A second

sample (15 ml) was filtered (Gelman glass fiber filter, Type -A/F, 25 mm)

in the field, preserved with 2 drops of mercuric chloride, and stored in

acid-washed scintillation vials. After field processing, the samples were

frozen (dry ice), and returned to the laboratory for analysis.

In the laboratory, nutrient concentrations were determined on an

Autotechnicon II Auto Analyzer. Filtered samples were used for the ana-

lysis of orthophosphate and (nitrate and nitrite) nitrogen. The basic

method for analysis of orthophosphate followed that of Murphy and Riley

(1962) as modified in Technicon Industrial Method No. 155-71W (1973) and

described by Glibert and Loder (1977). The basic method for analysis of

(nitrate and nitrite) nitrogen followed that of Technicon Industrial

Method No. 158-71W (1972) as described by Glibert and Loder (1977). Un-

filtered samples were used for the determination of total nitrogen and

total phosphorous. Analysis was performed on an Autotechnicon II Auto

Analyzer and followed the basic procedure suggested by D'Elia et al., (1977)

as modified by Edwards (unpublished).

Concentrations of chlorophyll a and phaeo-pigments were also deter-

2-4

mined from the bottom and surface water samples. From the half liter

samples, 20 ml was pipetted to a filtration apparatus consisting of Gel-

man glass fiber filters (type, -A/E, 25 mm). The filters were placed

in scintillation vials that were prewashed in 90% acetone. Saturated

magnesium carbonate solution (1 ml) was added and the vials were frozen

in the field.

In the laboratory, 9 ml of 100% acetone were added to the frozen

samples resulting in a 90% acetone extraction solution. The samples

were periodically agitated and storedat 50C for 24 hours. A Turner

fluorometer was used to determine chlorophyll a and phaeo-Pigments

according to the method of Yentsch and Menzel (1963). Further infor-

mation on the procedure is found in Holm-Hansen et al. (1965) and

Strickland and Parsons (1972).

Four types of gear were used to sample various animal communities

at NMF and SJ Creeks. Microscopic plankton were collected with a zoo-

plankton net and somewhat larger swimming organisms which live near the

bottom were collected with an epibenthic sled. Large bottom (benthic)

invertebrates and fishes were collected with an otter trawl and larger

subsurface fishes were caught in gill nets.

Zooplankton collections were made every two hours with a 30 cm dia-

meter net constructed of 153p mesh nytex (Fig. 2-1). A torpedo-type

flowmeter was mounted inside the mouth of the net to estimate the volume

of water filtered by the net as it was towed from a small boat. The

weighted net was lowered to the bottom, then towed against the current

for 90 seconds. During the tow, the boat speed was increased to allow

2-5

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~. . . ....... .. - -. -

X..

Ma~~~~~~~~~~~~~* ii

**SUS*******S*Mflp*! I! I~~~~~~~~~..fl..f.....U...~
B . _ _-----_----

MA .98.6 N A.~~~~~~~rrnum:.::uur::::::.. ga......
IN --a uu***u....u......sa avasu..s..fl a.m a EIM O
av"M NMfwas..D..m. n ymues&..u~.....f.-

Cans.as := Mm llM.0M..

A. zoopl~~~~~~~~'anktnntB nbnhcse

m m - --- - m m - mNMMU"DOMEMNN

the net to sample the entire water column from bottom to surface. The

sample was removed from the codend of the net and preserved in a 10%

borax buffered formalin solution with rose bengal. A second tow immed-

iately followed the first.

In addition to the bi-hourly collection during the 24-hour major

cruises at each creek, zooplankton collections were taken at high and low

tides at both creeks on the "mini" cruises. The same equipment and pro-

cedure were used at the Winyah Bay stations,

In the laboratory a 2 ml subsample was removed from a well-mixed

sample. Copepod crustaceans, which dominated the samples, were counted

and identified to species. All other organisms were identified to desig-

nated taxonomic categories and counted. Preliminary tests showed no sig-

nificant differences between subsample counts, so only one subsample was

counted. The processed 2 ml aliquot was remixed with the original sample

and stored in 10% buffered formalin.

Small motile organisms which live on or just above the bottom were

collected with an epibenthic sled (Fig. 2-1). The apparatus consists of

a rectangular steel frame (51 x 30 cm) which orients the mouth of a 365k

mesh nytex plankton net perpendicular to the bottom. This frame is

mounted on a horizontal frame which slides over the bottom on three skis.

The sled was pulled behind a small boat in the direction that the tidal

currents were moving. A marked towpath was followed in each four minute

tow. The volume of water filtered was estimated with a flowmeter mounted

inside of the net mouth. Three consecutive tows (replicates) were made

every two hours. The samples were preserved in a 10% borax buffered

2-7

formalin solution with rose bengal.

The same procedure was followed on the "mini" and Winyah Bay cruises.

Zooplankton and sled collections were made simultaneously so that the

results could be compared.

In the laboratory, entire samples were processed unless a large vol-

ume of detrital material occurred, in which case the sample was split.

All organisms were identified to the lowest possible taxon and counted.

Mysid shrimp and fish larvae were identified to species, counted, and

measured. The processed portion of the collection was remixed and the

original sample was stored in 10% buffered formalin.

Fish and macroinvertebrate collections were made during the major

cruises at both creeks with a 480 cm (16 ft.) headrope otter (shrimp)

trawl (Fig. 2-2). The body of the net is 38 mm (1� in.) stretch mesh

nylon and the cod bag is 32 mm (1� in.) stretch mesh nylon. The doors

are 61 x 30 cm (24 x 12 in.). A sinale tow was made alone a marked tow-

path every six hours. The net was pulled against tidal currents at the

speed of about three knots.

All organisms in the collections were identified to species. Large

specimens were measured and weighed in the field, but most crabs, shrimps,

squids, and fishes were returned to the laboratory. Blue crab width was

measured from point to point to the nearest millimeter. Penaeid shrimp

length was measured from the tip of the rostrum to the end of the cara-

pace (�1mm). Fish length was measured from the anterior extremity to

the end of the caudal fin (tail). Up to 100 of each species of inverte-

brates and fishes were measured in each collection. Total number and

2-8

.....�� �� ....... ..

::::"'~~~~����������~~~~...... ...~
~.i~i~.i~iiiiji~i..i~.. i:~~~--:'I~:::.......................iiiiiiiiiiiiiiiiiiiiiii

�������........~~~~~~~~~~~.. .. ..... . . . . . . . . .Ir

Figure 2-2� Generalized form of semi-balloon otter trawl used to collect macroinvertebrates and fishes.

weight were determined for each species in each collection. Gut content

analyses were conducted on all large fishes and representative subsamples

of smaller ones. Information on the reproductive condition of many spe-

cies was collected.

Gill nets were set at the beginning of each major cruise and inspec-

ted every three hours. Larqe quantities of detritus or strong tidal

currents which fouled the nets restricted the use of this qear durina

several cruises. Three 15 m (50 ft.) panels, one each of 7.6, 19.0, and

30.5 cm (3,7.5, and 12 in.) stretch monofilament webbing were set perpen-

dicular to the creek axis. Fishes and crabs were identified, counted,

and measured in the field.

2-10

CH{APTER 3. PHYSICAL MEASUREMENTS AND WATER CHEMISTRY

B ~~~~Air temperature and surface and bottom water temperatures at both

3 ~~~No Man's Friend (NMF) and South Jones (SJ) Creeks were highest from June

through September (greater than 25 0C and lowest 'in January and February

I ~~~(less than 120C (Fig. 3-1 and 3-2). Maximum surface and bottom water

temperatures at both creeks were recorded in June and July (approximate-

ly 300C). Minimum water temperature values near 40C occurred in January.
3 ~~~Air and water temperatures typically increased from January to June and

decreased from September to January.

Water temperature is primarily influenced by solar radiation. The

temperature of riverine Inputs and tidal flow from the sea also affect

the temperature regime at NMF and SO. Shallow basins such as Mud Bay

I ~~~are particularly susceptible to temperature variations due to atmospheric

I ~~~conditions. Wind can alter water temperature by removing heat from the

water through increasing evaporatio~n. High wind velocities may also cause

3 ~~~the breakdown and prevent further formation of a thermocline (temperature

stratification within the water column). Winds and high current veloci-

I ~~~ties also create highly turbid conditions which may affect water tempera-

5 ~~~ture. Relatively large die], diurnal, and seasonal water temperature

fluctuations were observed at NMF and SO.

I ~~~~The flooding of marsh surface and mudflats during high tides directly

3 ~~~~~~~~~~~~~3-1

30 -

Cruise 1 3 5 7 9 1 1 1 3 1 5 1 7
Month A S S 0 N N D J J F M M A M J J J A

o 20

O-I

Cruise 1 3 5 7 9 1 I 13 15 17
Month A S S 0 N N D J J F M M A M J J J A

Figure 3-1. Mean air temperatures for all cruises at NMF (above) and SJ
(below) Creeks. Vertical lines through the circles represent
plus or minus the standard error.

3-2

9.6'
U~~~~~~~~~~

1 4

O-
. . . . . . . . . . . . . . . . . .
Cruise 1 3 5 7 9 1 1 13 15 1 7
Month A S S 0 N N D J J F M M A M J J J A

.*.

28.8 -

o 19.2-
F-

9,.6' 9

0-
. . . . . . . . . . . . . . . . .
Cruise I 3 5 7 9 1 1 1 3 1 5 1 7
Month A S S 0 N N D J J F M M A M J J J A

Figure 3-2. Mean surface (above) and bottom (below) water temperatures at
NMF (dark circle) and SJ (open circle) Creeks. Vertical lines
through the circles represent plus or minus the standard error.

3-3

affects the water temperature. During the summer, exposed marsh may be-

come much warmer than the surrounding waterways, and water ebbing from

the intertidal zone after flood conditions can elevate water column tem-

perature. Conversely, exposed intertidal areas may be much cooler than

flooding waters during the winter resulting in increased temperatures of

the intertidal sediments and decreased water temperatures.

Salinity is also an important factor in determining water tempera-

tures. Fresh water has a higher specific heat than does salt water. This

means that more heat is required to warm a given amount of fresh water

than the same amount of salt water. Precipitation effects on water tem-

peratures are manifest in salinity changes.

Salinity has been defined as "the total amount of solid material, in

grams, contained in one kilogram of sea water when all the carbonate has

been converted to oxide, the bromide and iodine replaced by chlorine, and

all organic matter completely oxidized" (Cushing and Walsh, 1976). Ions

present in seawater and their percentage composition include sodium (30.4),

potassium (1.1), calcium (1.16), magnesium (3.7), chlorine (55.2), sulfate

(7.7), and carbonate (0.35). These ions plus strontium, bromide, and bo-

ric acid constitute more than 99% of the total salts in seawater (Reid

and Wood, 1976). The salinity of oceanic waters averages 35 parts per

thousand (o/oo), whereas freshwater is considerably less than i o/oo.

The proportion of dissolved salts in estuarine waters generally resembles

that of salt water, although the total concentration changes along the

length of the estuary (Reid and Wood, 1976).

Maximum values for surface salinity were recorded in February at

3-4

NMF (35.0 o/oo) and January at SJ (31.9 o/oo) (Fiqg. 3-3), Bottom salin-

ity was highest in January at NMF (36.0 o/oo) and June for SJ (34.4 o/oo).

Lowest surface and bottom salinities for both creeks were recorded in

March. Cruise to cruise variations in surface and bottom salinities

did not follow a regular pattern. Salinities for NMF and SJ primarily

result from the dilution of sea water by the freshwater river input. The

degree of dilution is dependent on the amount of freshwater entering the

estuary as well as tidal intrusion of sea water. Amount of sea water

entering the estuary is related to lunar phase (ie. spring and neap

tides), wind, and meteorological conditions.

Average surface and bottom salinities were generally lower at SJ

than at NMF reflecting the greater contribution of high salinity North

Inlet water to NMF (refer to Chapter 1). Salinities varied considerably

over the sample period and variations on the order of 15-20 o/oo were com-

mon. Maximum salinities were generally recorded near the slack flood

tide and minimum values near slack ebb tide. Large differences between

surface and bottom salinities throughout many of the tidal stages ob-

served were related to the formation and maintenance of a halocline

(light freshwater flowing over denser brackish water). Haloclines were

only observed to occur during periods of low turbulent mixing when wind

and current velocities were low. For example, the halocline observed in

NMF in January, where surface salinities averaged 11.5 o/oo less than

bottom salinities, occurred during a period when tidal amplitude (1.2 m)

and current velocity were low, and wind speeds were usually less than

5 mph. Over half of the hourly observations were characterized by wind

speeds of less than 2 mph. A 17 o/oo salinity difference between surface

3-5

32-

�;24- ,

~~~I~~~~~~~~~~~ 6~
c

� . � . . . . . . . . . . . . . . . .
Cruise I 3 5 7 9 II 1 3 5 17
Month A S S 0 N N D J J F M M A M J J J A

o
o
3 -

=~~~~~~~~~~~~
24

0 1 6

i . . . . . . . . . . . . . . . . . .
Cruise I 3 5 7 9 1 I 1 3 1 5 17
Month A S S 0 N N D J J F M M A M J J J A

Figure 3-3. Mean surface (above) and bottom (below) salinities at NMF
(dark circle) and SJ (open circle) Creeks. Vertical lines
through the circles represent plus or minus the standard
error.

3-6

and bottom waters was observed during the last four hours of the ebb tide.

The stratification and mixing of water masses of different salinity and

chemical content probably affects the distribution of many organisms in

the two creeks and the maintenance of a permanent community structure.

Vertical visibility was measured with a Secchi disk during every

cruise. Secchi disk transparency is directly related to the vertical

coefficient of light absorbtion which delineates the region from the sur-

face to the depth at which 99% of the surface light has disappeared (Cole,

1975). This region is referred to as the euphotic zone, and is ecologi-

cally important because little or no photosynthesis can occur below this

zone.

Secchi disk visibility in estuarine areas is primarily affected by

turbidity, which is defined as the concentration of particulate matter

suspended in the water column. The major component responsible for estu-

arine turbidity is silt and its concentration is dependent on rainfall,

currents, wind, agricultural runoff, and erosion within the creeks. High

densities of plankton and detrital material also affect light penetration

serving to effectively reduce the depth of the euphotic zone.

Average secchi disk visibility at NMF and SJ was lowest in June

(0.32-0.35 m) and highest in January and February (1.2-1.84 m). Secchi

disk visibility at NMF was approximately 0.5 m or less for the period

August through October, 1980, and increased steadily to a maximum of 1.84m

in January, 1981 (Fig. 3-4), then declined sharply to approximately 0.5 m

in March, 1981. Secchi disk visibility at SJ followed a similar pattern

with the maximum value of 1.65 m occurring in February, 1981. However,

3-7

E 1.2

0.6

Cruise I 3 5 7 9 1 1 13 15 17
Month A S S 0 N N D J J F M M A M J J J A

1 .8 '

1.2

0.6 6

minus the standard error.
3-8

Cruise 1 3 5 7 9 1 1 1 3 1 5 1 7
Month A S S O N N D J J F M M A M J J JA

Figure 3-4. Mean secchi disk visibilities at NMF (above) and SJ (below)
Creeks. Vertical lines through the circles represent plus or
minus the standard error.

3-8

secchi disk visibility in SJ showed a pronounced decline during the

second January sampling date, which was not evident in the NMF data.

Also, secchi disk readings at SJ fluctuated more during March through

August, 1981, than did the corresponding NMF data.

Low secchi disk readings from March through October corresponded

to the increased abundance of phytoplankton and detritus in the water

column and most intense periods of agricultural activity in the upper

estuary. High secchi disk visibility corresponded to periods of low pro-

ductivity (refer to Chapter 4) and minimal agricultural runoff. Vertical

visibility generally followed a similar pattern at NMF and SJ, Higher

variability exhibited by the data in SO during March through August prob-

ably resulted from a number of factors including current velocity, wind,

and detrital concentrations. The large decrease in average secchi disk

visibility in late January was apparently the result of a localized phy-

toplankton bloom. Concentrations of both chlorophyll a and phaeo-pigments

(refer to Fig. 4-1 and 4-2 in Chapter 4) in SO were almost twice as large

as those recorded in NMF.

Water sample analyses were conducted to determine the relative con-

centration of total nitrogen and its various forms in the two creeks.

Nitrogen is essential in the synthesis of protein which is a major con-

stituent of living cells and, therefore, is essential to the existence of

an ecosystem. Atmospheric nitrogen acts as a reservoir for a complex

cycle involving plants, animals, and various forms of the element. Ni-

trogenous compounds are made available to the estuarine environment by

bacterial fixation of elemental nitrogen, precipitation, surface runoff,

riverine inputs, photochemical and lightning fixation, decomposing plant

3-9

and animal tissues, and animal excretory products (amino acids, urea,

uric acid, anmmnonia). Available nitrogen is transformed into nitrates

through bacterial action. Ammonium-nitrogen and, to a lesser extent,

nitrite-nitrogen can be utilized by some phytoplankton species, although

nitrate-nitrogen is primarily taken up by the cells and transformed into

complex proteins (Russell-Hunter, 1970). Concentrations of inorganic

nitrogen compounds (ammonia, nitrite, nitrate) regulate the productivity

of an aquatic ecosystem because they are used in the synthesis of plant

proteins which form the base of the aquatic food web.

Surface total nitrogen at NMF and SJ was highest in July (approxi-

mately 76 jig At.N/l) and lowest in December (26 and 32 vg At.N/l, respec-

tively) (Fig. 3-5). Bottom total nitrogen was highest in June at NMF

( 83 pg At.N/l) and July at SJ (80 pg At.N/l). Lowest bottom total ni-

trogen values were recorded at NMF and SJ in December (21 and 25 pg At.N/l

respectively). Total nitrogen in both creeks at surface and bottom gen-

erally exhibited a similar pattern (Fig. 3-5). Values decreased from

August or September to a minimum in December and typically increased from

December through June or July.

Nitrate-nitrite values at NMF and SJ appear to exhibit a bimodal

pattern. Maximum values were recorded in November or December and March

or April (Fig. 3-6). Surface nitrate-nitrite concentrations were highest

in March and December at NMF (6.8 and 3.5 pg At.N/l) and March and Novem-

ber at SJ (8.2 and 6.3 pg At.N/l). Lowest values were recorded in July

at NMF (less than 0.1 pg At.N/l) and August at SJ (0.5 pg At.N/l). Bottom

nitrate-nitrite values were highest in November and April at NMF (1.7 and

1.5 pg At.N/l) and December and March at SJ (3.7 and 3.1 pg At.N/l). At

3-10.

84'
I~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

I~~~~

R' 28 e

Cruise 1 3 5 7 9 i I 13 15 17
Month A S N D J M A J J

. 56
O-
T

* ~~~~~0*

Cruise I 3 5 7 9 II 13 1 5 17
Month A S N D J M A J J

Figure 3-5. Mean surface (above) and bottom (below) concentrations of total
nitrogen at NMF (dark circle) and SJ (open circle) Creeks.
Vertical lines through the circles represent plus or minus the
standard error.

3-11

z 6

N - 34 K

O-

Cruise I 3 5 7 9 1 1 13 15 1 7
Month A S N D J M A J J

96- -

z 1

3 .1

Cruise 1 3 5 7 9 1 1 13 15 1 7
Month A S N D J M A J J

Figure 3-6. Mean surface (above) and bottom (below) concentrations of
(nitrate and nitrite) nitrogen at NMF (dark circle) and SJ
(open circle) Creeks. Vertical lines through the circles
represent plus or minus the standard error.

3-12

both creeks, bottom nitrate-nitrite values were lowest in August C0,6 pg

At.N/1).

High values for total nitrogen at both creeks from June through Sep-

tember correspond to periods of high productivity when concentrations of

chlorophyll a and phaeo-pigments are greatest (Chapter 4). As phytoplank-

ton productivity increases, simultaneousincreases in animal biomass may

be expected. During this period, metabolic activity increases and higher

levels of animal excretion of nitrogen wastes and decomposition of plant

and animal tissues occur, thereby increasing the concentrations of total

nitrogen in the water column.

Low values for nitrate-nitrite at both creeks during June through

September also correspond to periods of maximum concentrations of chloro-

phyll a. Nitrate-nitrogen and nitrite-nitrogen are easily assimilated

by phytoplankton. During periods of peak abundance of phytoplankton,

nitrate (N) and nitrite (N) are assimilated by the phytoplankton as fast

as they become available. Conversely, high nitrate-nitrite values can be

related to periods of low utilization by phytoplankton (low chlorophyll a

values), and may represent a disproportionate share of the total nitrogen

present in the water column during these times.

Seasonal data for nitrate-nitrogen reflect findings from other salt

marsh and estuarine studies where higher concentrations were found to oc-

cur during winter months and lower concentrations during the summer (Norall

and Mathieson, 1976; Mauriello and Winfield, 1978; Daly and Mathieson,

1981). Declines in nutrient concentrations have been related to phyto-

plankton productivity (Thayer, 1971) and phytoplankton density has been

3-13

shown to have a significant inverse relationship to nitrate (Toner, 1981).
In estuarine studies near Beaufort, NC, nitrogen availability has been

suggested to be the most critical factor in determining rates of photosyn-

thesis (Thayer, 1974).

Water samples collected on major cruises were also analysed for phos-

phorus. Phosphorus is vital in the operation of cellular energy transfer

systems. Phosphorus is typically scarce in unpolluted environments and

is often a major limiting factor to aquatic productivity. Concentration

of phosphorus in estuarine waters is primarily affected by basin morphom-

etry, geochemistry of the watershed, input of organic matter, organic

metabolism in the water column, and the rate of loss of phosphorus to the

sediments (Reid and Wood, 1976). In a natural salt marsh in Delaware,

data indicated that total and inorganic phosphorus concentrations were

directly related to salinity and concentrations of the three forms of

phosphorus (total, organic, and inorganic) were directly related to tide

stage, lunar phase, and day of year (Reimold and Daiber, 1970), Precipi-

tation may also contribute significant quantities of nutrients to salt

marsh and estuarine environments (Reimold and Daiber, 1970).

In estuaries a large pool of phosphorus is retained in the sediments

(Rochford, 1951; Pomeroy et al.,1965 and 1969; Pomeroy, 1970).

This pool of phosphorus is made available to the aquatic environment by

ion exchanges between sediments and overlying water and by microorganisms

(Gooch, 1968; Pomeroy et al.,1969). Spartina alterniflora may also play

an active role in the circulation of phosphorus in the sediments to the

marsh surface (Pomeroy et al.,1969).

Decomposition also serves to increase concentrations of phosphorus

3-.14

in the aquatic environment. Decomposition results in the direct release

of nutrients from dead organic material to the environment. The impor-

tance of the Spartina detritus food chain in recirculation of nutrients

has been demonstrated (Odum and dela Cruz,1967). Bacterial assimilation

of detrital phosphorus and consequent grazing of detrital bacteria by

zooplankton results in very rapid turnover times (approximately 2 minutes)

of the free pool of phosphate (Barsdate et al., 1974).

Phosphorus, usually in the form of orthophosphate, is rapidly assi-

milated by phytoplankton as soon as it is made available and is then

passed on to higher trophic levels through herbivory and subsequent pre-

dation. Uptake of orthophosphate in surface waters and in vertical pro-

files has been shown to be directly proportional to the standing stocks

of phytoplankton and bacterioplankton (Krempin et al.,1981).

Surface total phosphorus concentration was highest in July at NMF

(4.1 pg At.P/l) and June at SJ (2.8 pg At.P/l) (Fig. 3-7). Surface total

phosphorus was lowest in January at both creeks (0.6 pg At.P/l). Bottom

total phosphorus was highest in June at NMF (5.4 pg At.P/l) and September

at SJ (4.4 pg At.P/l). Bottom total phosphorus was lowest in January at

both NMF and SJ (0.2 and O.4 pg At.P/l, respectively).

Seasonal values for orthophosphate-phosphorus apparently follow a bi-

modal pattern with peaks occurring in November or December and June or

July. Concentrations of surface orthophosphate-phosphorus were highest

in November at NMF (0.7 pg At.P/l) and December at SJ (0.6 pg At.P/l)

and lowest in January at both creeks (0.2 pg At.P/l) (Fig. 3-8). Concen-

trations of bottom orthophosphate-phosphorus were highest in November at

3-15

4.
0.

Cruise 1 3 5 7 9 1 1 1 3 I 5 1 7
Month A S N D J M A J J

3-16

- 4 l

ma "s~~~~~~~,,, a,,,.
N0

'5 -,

. . . . . .I

Cruise I 3 5 7 9 II 1 3 1 5 17
Month A S N 0 J M A J J

Figure 3-7. Mean surface (above) and bottom (below) concentrations of total
phosphorus at NMF (dark circle) and SJ (open circle) Creeks.
Vertical lines through the circles represent plus or minus the
standard error.

3-16

II�

0.26 -

0.26'

Cruise 1 3 5 7 9 1 1 13 15 17
Month A S N D J M A J J

0.78

0.52 ,
o.
I

0.26

Cruise I 3 5 7 9 1 I 13 15 17
Month A S N D J M A J J

Figure 3-8. Mean surface (above) and bottom (below) concentrations of
orthophosphate-phosphorous at NMF (dark circle) and SJ (open
circle) Creeks. Vertical lines through the circles represent
plus or minus the standard error.

3-17

NMF and SJ (0.8 and 0.5 pg At.p/l, respectively). Lowest values for

bottom orthophosphate-phosphorus (0.2 pg At.P/l) were recorded in March

at NMF and January at SJ.

High values for surface and bottom total phosphorus at both creeks

during June through September may reflect the high concentration of phy-

toplankton and detritus in the water. Conversely, low surface and bottom

values of total phosphorus in January in both creeks may reflect the low

density of phytoplankton and detrital matter in the water. Seasonal pat-

terns of phosphorus concentration closely resembled those of a Delaware

salt marsh (Reimold and Daiber, 1970).

High surface and bottom orthophosphate values at NMF and SJ in Novem-

ber or December and June or July may indicate that orthophosphate is being

made available to the environment faster than it can be utilized. Low

values in January and March may be explained by the increase in phyto-

plankton biomass and utilization of the orthophosphate. Seasonal ortho-

phosphate concentration patterns reflect similar findings from Flax Pond,

a tidal marsh on Long Island (Woodwell and Whitney, 1977).

3-18

CHAPTER 4. PHYTOPLANKTON

A biotic community is defined as an association of populations of

3 ~~~microorganisms, plants, and animals. A biotic cormmunity and the physico-

chemical environment in which it exists constitute an ecosystem. Complex

I ~~~interrelationships exist between the different groups of organisms and

3 ~~~the pool of nutrients in the environment. Knowledge of the basic rela-

tionships and interdependencies among the three major groups of organisms

3 ~~~(bacteria, plants, animals) and the abiotic environment are essential to

the understanding of an ecosystem. Of particular interest to ecologists

I ~~~and managers are the trophic dynamics (relating to nutrition) of an eco-

3 ~~~system.

Green plants are autotrophic organisms or primary producers which

can synthesize complex organic carbon compounds from simple inorganic sub-

3 ~~~stances. This process is known as photosynthesis and involves the conver-

sion of carbon dioxide and water into simple sugars by a chlorophyll me-

3 ~~~diated chemical reaction. The simple sugars produced are then converted

into complex substances (starches, oils, etc.) and stored as food reserves

I ~~~in the plant cells. In estuaries, phytoplankton are primarily responsible

3 ~~~for this photochemical reaction, and their abundance in the aquatic eco-

system at a particular time is referred to as the standing crop of pro-

3 ~~~ducers. Other living organisms, including most animals and decomposers

3 ~~~~~~~~~~~~4-1

(bacteria and fungi), are termed heterotrophic organisms, or consumers,

because they require prefabricated complex compounds for their nutrition.

Because of their capacity to photosynthesize, plants occupy the base

of almost all food chains. There are two basic food chains in estua'ine

environments. In one, rooted angiosperms and epiphytes are the primary

producers, and in the other, phytoplankton are the primary producers

(Russell-Hunter, 1970). In either case, the generated plant tissues are

fed upon either directly by grazing (herbivory), or indirectly by feeding

on dead plant materials and decomposers (detritivory). There may be

several steps involved in a single food chain. For example, a single

food chain may include a diatom species, a herbivorous zooplankton spe-

cies, two predaceous zooplankton species, a smaller fish, and a larger

fish. The production of fish and invertebrate tissue in an estuary or

salt marsh is obviously directly related to the productivity of the green

plants. Consequently, in order to understand fluctuations in the popula-

tions of zooplankton, epibenthic and benthic organisms and fish, it is

also necessary to understand primary productivity in the environment.

Phytoplankton represent a high proportion of the standing crop of

primary producers in estuaries and salt marsh creeks. Phytoplankton are

microscopic aquatic plants which are primarily transported by tidal and

wind driven currents. Phytoplankton species are classified according to

life cycle characteristics, size, and location in the water column. Holo-

plankton refers to species that are planktonic throughout their life cy-

cle. Meroplankton describes species which spend a portion of their life

cycle as plankton. Tychoplanktonic species are benthic microalgae which

may become suspended in the water column by turbulent forces.

4-2

Size classes of phytoplankton include ultraplankton (!55ym), nano-

plankton (5-75vm) (Smith, 1977) and net plankton (those phytoplankters

which are retained in a standard phytoplankton net with a 75pm mesh).

Although net plankton are the most conspicuous members of the phytoplank-

ton community, recent research indicates that ultraplankton and nanoplank-

ton may be responsible for the majority of primary productivity in estu-

arine and salt marsh areas. Van Valkenburg and Flemur (1974) found that

phytoplankton less than 10pm in size were more abundant than the net

plankton during all seasons. Nanoplankton and ultraplankton species rep-

resented 55 to 100% of the total productivity, as determined by studies

of radioactive carbon uptake. In the Chesapeake Bay, McCarthy et al.

(1974) found that small planktonic species (<35vim) accounted for 56.6

to 89.6% of the productivity. The abundance of nanoplankton was not re-

lated to the salinity gradient, indicating the importance of this group

to the entire estuarine ecosystem.

Pelagic phytoplankton refers to species found in the water column,

and benthic phytoplankton are associated with substrates. Phytoneuston

are located at or near the air/water interface. Recent work indicates

that phytoneuston is an important component of the total estuarine phyto-

plankton and contributes a disproportionately large share to the total

primary productivity (Manzi et al.,1977). Phytoneuston are also of eco-

logical significance in disturbed systems because they are the first phy-

toplanktonic component affected by chemical spills (Sandifer et al.,1980).

Despite wide fluctuations in environmental factors, estuaries and

salt marshes represent highly productive areas for phytoplankton,. In

fact, salt marshes are among the most productive natural areas on earth

4-3

(Schelske and Odum, 1962). Zingmark (1977) estimated the annual rate of

benthic algal production in nearby North Inlet, South Carolina to be

685gC/m2/yr. Values of 4-9gC/m2/yr determined by Steele and Baird (1968)

for an intertidal sandy beach contrast sharply to these estuarine mud-

flat values.

Estuarine, salt marsh, and coastal marine phytoplankton belong to

several plant divisions including Cyanophyta, Chlorophyta, Euglenophyta,

Bacillariophyta, Chrysophyta, Cryptophyta, Pyrrhophyta (for complete

lists of phytoplankton species refer to Sandifer et al.,1980 and Manzi

and Zingmark, 1978). Benthic marine algae primarily belong to the Divi-

sions Cyanophyta and Chlorophyta. Dominant members of the estuarine phy-

toplankton community include members of the Divisions Bacillariophyta

(golden-brown algae) and Pyrrhophyta.

Diatoms (Division Bacillariophyta) are considered to be very impor-

tant in the cycling of energy in natural waters and are often regarded

as the most important autotrophs in estuarine and coastal marine waters.

Diatoms are unicellular, possess cell walls made of silica, store food

substances as carbohydrates or oils, and are abundant in the water column

and attached to substrates. Diatoms are constructed of two siliceous

valves which overlap in a pill-box configuration. They are divided into

two major groups based on the morphology of these valves; centric dia-

toms have a valve that radiates outward from a central point and pennate

diatoms are boat shaped in form.

Dinoflagellates belong to the Division Pyrrhophyta. They possess

two flagella, are motile, and are either autotrophic (absorb nutrients

4-4

in the water column) or heterotrophic (feed upon other orgonisms.). Some

species are bioluminescent and others are known to produce the toxins

that are associated with red tides.

There are four principal methods of determining primary productivity

in aquatic ecosystems: radioactive tracer techniques, rate of oxygen pro-

duction as a measure of net production over a period of time, direct

counting of individual plant cells, and assessment of total chlorophyll a

content of a measured volume of water (Russell-Hunter, 1970). The pro-

ductivity values obtained reflect the total standing crop of phytoplank-

ton present in the water. Direct counting and identification of individ-

ual plant cells is the only method capable of assessing the contribution

of diatoms, dinoflagellates, and other important components to the phyto-

plankton standing crop. Unfortunately, this tedious and time consuming

method is not feasible in a study of the magnitude of the present one.

Assessments of chlorophyll a concentrations were used as indicators

of primary productivity in this study, Determination of chlorophyll a

is a rapid chemical method for quantifying the amount of living plant

matter in the water column, but the relationship between living organic

plant material and the quantity of plant pigment is highly variable, de-

pending upon the species composition of the phytoplankton in the water

as well as their state of nutrition (Strickland and Parsons, 1972). De-

spite this limitation, assessment of chlorophyll a still serves as a use-

ful tool, providing a relative index of seasonal and diurnal changes in

the standing crop of phytoplankton.

I Values recorded for surface chlorophyll a in SJ and NMF represent a

4-5

bimodal pattern with peaks occurring in late summer and winter (January)

(Fig. 4-1). Highest concentrations of surface chlorophyll a occurred in

September at NMF (16.0 mg/m3) and July at SJ (14.9 mg/mr3). Lowest concen-

trations of surface chlorophyll a occurred in December at NMF and SJ

(1.9 mg/m3 and 1.7 mg/m3, respectively). Highest concentrations of bot-

tom chlorophyll a occurred in July at NMF and SJ (16.6 mg/mi3 and 13.3
3
mg/m , respectively) and lowest values occurred in December at NMF and SJ

(1.0 mg/m3 and 1.6 mg/m3, respectively). Concentrations of chlorophyll a

at both creeks were generally higher in surface water samples than bot-

tom water samples. The January peak in chlorophyll a concentrations at

both NMF and SJ was observed only in surface samples. Bottom chlorophyll

a concentrations in SJ in January showed only a slight increase over

adjacent sampling dates; no increase was observed in values recorded for I

NMF. The January peak probably represented a phytoplankton bloom involv-

ing relatively few species. Higher concentrations of chlorophyll a in

the surface samples in both creeks reflected the greater contribution of

phytoplankton in the euphotic zone to primary productivity. One inter-

esting aspect of the chlorophyll a data is the absence of a large spring

phytoplankton bloom, which is almost certainly a reflection of the sam-

pling regime. Due to the ephemeral nature of the spring phytoplankton

bloom, there is a high probability that sampling at six week intervals

missed the bloom entirely. High concentrations of chlorophyll a in late

summer and fall samples are probably annual events which reflect optimal I

conditions of solar radiation, temperature and nutrient availability.

The abundance of phytoplankton in summer and fall samples is expected to

be reflected in the ultimate population sizes of zooplankton during the

period.

4-6

I~~~~~~~~~

I~~~~~~~~

Cruise 1 3 5 7 9 1 13 15 17
Month A S N D J M A J J
I ~~~~~~~18 -

I 2 ' ~ I

0. �
*~~~~~~~~~ -*

Cruise I 3 5 7 9 I I 13 15 17
Month A S N D J M A J J

Figure 4-1. Mean surface (above) and bottom (below) concentrations of
chlorophyll a at NMF (dark circle) and SJ (open circle)
Creeks. Vertical lines through the circles indicate plus
or minus the standard error.

4-7

Marshall (1980) described a bimodal pattern of phytoplankton popu-

lation peaks with fall and spring maxima for lower Chesapeake Bay and

Old Plantation Creek (a salt marsh intertidal creek). He found that

creek waters had a greater assortment of flagellates, smaller diatoms

typically associated with mud flats and vegetation within the creek com-

plex, and representatives from other phytoplankton taxa.

A wide array of factors affect abundance and succession of phyto-

plankton in estuaries and salt marshes, and are summarized by Rice and

Ferguson (1975) (Table 4-1). Seliger et al, (1981) found that patchiness

(disjunct distribution) of phytoplankton and chlorophyll a in Chesapeake

Bay was related to the formation and maintenance of frontal and inter-

frontal systems. Density flow forcing was responsible for the retention

of different phytoplankton populations within different regions of the

Bay. Toner (1981) demonstrated a strong statistical relationship between

two factors (wind and solar energy) and the standing crop of phytoplankton

in Mount Hope Bay, Massachusetts. Wind affects phytoplankton production

by maintaining phytoplankton in the water column and retarding settling,

resuspending nutrients trapped in the sediments, and circulating phyto-

plankton throughout the euphotic zone where photosynthesis occurs.

Therriault and Platt (1981) found that wind speeds (� 5 m/s) resulted in

a uniform spatial distribution of phytoplankton. Patchy distributions

during periods of low wind speeds (< 5 m/s) were related to differences

in production efficiency which was linked to the physico-chemical charac-

teristics of the environment. Temporally related variables, including

tidal flushing and diurnal changes in photosynthetic rates, may often be

the most important determinants of phytoplankton abundance and primary

4-8

Table 4-1. Natural and man-imposed conditions which determine levels and rates of change of factors
affecting abundance and succession of estuarine phytoplankton (Rice and Ferguson, 1975).

Factors Natural Conditions Man-imoosed Conditions

Salinity Precipitation, runoff, evaporation, Water impoundment, channelization, dredge
circulation of water and fill , mosquito ditching

Temperature Latitude, season, weather, time of Heated effluent, dams, canals and water-
day, circulation of water ways, stream channel ization

Light Intensity

At surface Latitude, season, weather, time of Air pollution -smog
day

Below surface Reflection, absorption, scattering Dredging, waste dumping, erosion

Nutrients Drainage, runoff, circulation of Sewage and industrial wastes, urban and
water, sediments agricultural drainage, erosion

Metabol ites Living and dead plants and animals Sewage, urban and agricultural drainage,
erosion

Toxic Substances
Petroleum ~~~~~~Deposits Leads and spills during drilling, trans-
Petrol eum ~~~~~~~~~~~~~~~~~~~port, storage, use of disposal

Radionucl ides Primordial deposits, cosmic-ray Fallout, nuclear power reactors, other
produced releases

Heavy Metals Terrestrial deposits, sediments, Industrial and domestic wastes, mining,
land drainage erosion

Synthetic Toxicants Industrial,agricultural , domestic use

productivity (Moll and Rohlf, 1981). Baillie and Welsh (1980) emphasized

the importance of tidal resuspension on the distribution of intertidal

algae (an important contributor to primary productivity) in an estuary

on Long Island Sound.

Many studies have examined the relationship between phytoplankton

and zooplankton. Zooplankton grazing pressure acts to shape the general

form of the chlorophyll profile in the ocean (Longhurst, 1976; Herman and

Dauphin6e, 1979; Ortner, Wiebe, and Cox, 1980; Longhurst and Herman, 1981).

Zooplankton biomass and fecundity are strongly related to phytoplankton

biomass in lakes and estuaries (Comita and Anderson, 1959; McCauley and

Kalff, 1981; Toner, 1981). Growth and longevity of zooplankton have also

been shown to be limited by nanoplankton availability (Vijverburg, 1976).

Water samples collected during major cruises were also analysed for

phaeo-pigment concentrations. Highest surface phaeo-pigment concentra-

tions were recorded in July at NMF (5.8 mg/m3) and September in SJ (4.8

mg/m3) (Fig. 4-2). Lowest surface phaeo-pigment values occurred in Decem-

ber at both NMF and SJ (1.1 mg/m3 and 1.2 mg/m3, respectively), Highest

bottom phaeo-pigment values were recorded in April at NMF (6.5 mg/m3) and

September at SJ (7.9 mg/m3). Lowest values occurred in January at NMF and

SJ (0.6 mg/m3and 1.3 mg/m3, respectively).

Degradation products of chlorophyll may constitute a significant por-

tion of the total green pigments in the water column. Typically, phaeo-

phytin and phaeophorbide (collectively termed phaeo-pigments) represent

the greatest percentage of chlorophyll degradation products (Strickland

and parsons, 1972). Determination of phaeo-pigments serves as a useful

4-10

O 3

Month A S N D J M A J J

9- 9

~I~~~~*

Cruise I 3 5 7 9 1 1 13 15 17
Month A S N D J M A J J

Figure 4-2. Mean surface (above) and bottom (below) concentrations of
phaeo-pigments at NMF (dark circle) and SJ (open circle)
Creeks. Vertical lines through the circles represent plus
or minus the standard error.

4-11

tool in determining relative rates of phytoplankton turnover. High con-

centrations of phaeo-pigments in the water would be expected during peri-

ods of heavy grazing by zooplankton (Strickland and Parsons, 1972) and

massive die-offs following phytoplankton blooms.

Seasonal patterns of phaeo-pigment concentrations closely resembled

patterns described for chlorophyll a concentrations, and reflected the

turnover of phytoplankton resulting from zooplankton grazing or natural

attrition. Surface concentrations of phaeo-pigment in both creeks were

lower than bottom concentrations during the warmer months (April-Septem-

ber), higher in January, and variable in November, December, and March.

Higher concentrations of phaeo-pigment in surface waters during January

reflected phytoplankton turnover of the bloom which was detected by peaks

in chlorophyll a concentrations. Bottom concentrations increased after

January as dead cells settled to the sediments and remained higher than

surface concentrations during the highly productive warmer months.

4-12

CHAPTER 5. ZOOPLANKTON

Plankton (from the greek word "planktos", meaning "drifters of the

sea") are microscopic organisms, both plant (phytoplankton) and animal

(zooplankton), which are carried more or less passively in water currents.

Although most zooplankton are capable of weak swimming movements or can

control their rate of sinking and rising, they are not strong enough to

move against most currents. In most aquatic habitats, the zooplankton

community is a diverse assemblage of organisms containing members from

many invertebrate phyla as well as young stages of fish. The community

can be subdivided into the holoplankton, which are permanent members of

the plankton, and meroplankton, which temporarily exist as plankton for

a limited period (usually during larval development). Zooplankton range

in size from about 0.01 mm to over a meter (in the case of some jelly-

fish), but most of them are under 1.0 mm, and the animals discussed in

this chapter rarely are over I cm in longest dimension.

Many zooplankton, especially the smaller forms, are herbivorous,

feeding on microscopic phytoplankton (Deason, 1980; Ryther and Sanders,

1980). Studies of feeding in zooplankton (e.g. Heinle et al., 1977) have

revealed, however, that many are also detritivores, which feed on dead

organic particles or the layers of decomposers surrounding such parti-

cles. In addition, many zooplankton are predaceous and feed on smaller

5-1

zooplankton (e.g., Cooper, 1980; Pearre, 1981). Several studies have

demonstrated that many species are in fact generalists which can switch

their mode of feeding between herbivory, carnivory and detritivory, de-

pending upon which food sources are most available (e.g., Lonsdale et al.,

1978). Recent evidence (Porter, 1976; Epp and Lewis, 1981) has even im-

plied that zooplankton have symbiotic relations with some phytoplankton,

gaining nutrition while providing shelter and/or nutrients.

The zooplankton in turn form a vital link in aquatic food chains,

transferring energy from phytoplankton or detritus production to higher

trophic levels, such as fish and shellfish. The importance of this link

cannot be ignored, since most commercially important fish and shellfish

have young or larval stages which are members of, and predators on, the

zooplankton community. Adults of most species are also linked to the

zooplankton, either by feeding directly on them or on species which do.

Impacts of human activities on zooplankton can therefore influence pro-

ductivity or survival of commercially important species by affecting

their young or the food of their young, as well as the adults themselves.

Zooplankton are usually distributed in patches in aquatic environ-

ments. Within a given water mass, they are capable of vertical and hori-

zontal movement, and may change their local distribution quite regularly.

In deep offshore waters many zooplankton undergo regular diurnal vertical

migrations to the surface and back to deeper water (Russell, 1927). In

shallow waters, some forms have been shown to change their vertical dis-

tribution in accordance with light or tide levels, and the abundance of

such species changes drastically over a tide cycle or 24-hour period

(Cronin and Forward, 1979; Stancyk, unpublished). The causes of such

5-2

movements and patchiness are not well known, but factors such as phyto-

plankton abundance, light, turbidity, current speed and direction, and

predators may all be important. One effect of plankton patchiness is

that adequate representation of the community on the basis of a few sam-

ples is usually impossible, because even simultaneous replicates may be

quite dissimilar. Consequently, samples taken frequently over long peri-

ods of time are necessary to adequately characterize the zooplankton com-

munity in an area.

The makeup of zooplankton communities also varies from water mass

to water mass, because individual zooplankton species are sensitive to

physical and biological parameters such as salinity, temperature, tides,

turbidity, food availability and predators. At least seven different

zooplankton communities have been identified in coastal South Carolina,

including offshore, nearshore marine, estuarine, brackish impoundments,

riverine, palustrine and lacustrine (Sandifer et al.,1980). Although

there is overlap in species composition between these communities, each

is characterized by a different suite of dominants, as well as by differ-

ent proportions of meroplanktonic/holoplanktonic forms. For instance,

lacustrine habitats, or lakes, are dominated by small crustaceans called

cladocerans, and have few larval forms, while nearshore marine systems

are dominated by a few species of copepods and a large meroplanktonic

component.

Because of its diversity and the wide size range of its members, any

zooplankton community cannot be characterized completely with just one

type of sampling gear. Meshes of nets select for certain sizes within

the community, letting smaller members pass. In addition, larger, more

5-3

motile forms can detect and avoid nets, so counts of these forms are

usually underestimates of their real numbers. The problem can be solved

by using more than one sampling device, but this is often impossible be-
cause of limited time or funds to process samples. Most zooplankton
studies therefore involve a description of some subset of the total zoo-
plankton community, and this report is no exception, The 153 micron (1)

mesh net used in this study selected for microzooplankton (153-300p;
Unesco, 1968) and weakly swimming larvae, and undersampled such forms as

the small protozoans and holoplankton larvae (nanoplankton) and the larg-

er, stronger-swimming shrimp and fish larvae. Many of the latter group

were captured in the epibenthic sled, however, and are discussed in

Chapter 6. General reference works which are useful in the study of

zooplankton include: Raymont (1963); Unesco (1968); and Smith

(1977).

Although the Winyah Bay-North Inlet ecosystems contain a great di-

versity of planktonic forms (see Tables 5-1 and 9-2), there are some
species or groups which tend to dominate in numbers and biomass. Crus-
taceans in particular are dominant forms in planktonic systems. They
are members of the phylum Arthropoda, and include the familiar barnacles,
crabs, shrimps, lobsters, and crayfish, as well as numerous less familiar
groups, such as copepods, amphipods, isopods, mysids, and ostracods.
Crustaceans are characterized by the possession of an exoskeleton, or

hard outer shell, which must be shed as they grow. Most crustaceans,
especially in estuarine or marine systems, protect or brood their young

for part of their development, then release them as larvae. Larvae gen-
erally go through several molts or stages before becoming adults, and

5-4

Table 5-1. Relative abundance of zooplankton on major cruises at NMF and SJ.
Blanks indicate no organisms were present. Abbreviations are:
R = Rare (1 - 100/m3), C = Common (101 - 1000/m3), A= Abundant
( > 1000/m3). NMF = No Man's Friend Creek. SJ = South Jones Creek.

DATE AUG SEP NOV DEC JAN MAR APR JUN JUL
CRUISE NO. 1 3 5 7 9 11 13 15 17
STATION NF SJ NF SJ NF SJ NF SJ NF SJ NF SJ NF SJ NF SJ NF SJ
Copepods:
Acartia tonsa AA A A C C C R C C C R A A A A A A
Acartia copepodids A A A A C C C C R R R R A A A A C R
Centropages hamatus R R R R R R R R
C. typicus R
C. furcatua R R R
Eurytemora affinis R R R R R R
Labidocera aestiva R R R R R R R R
Parvocalanus crassirostris AA A A C C C C C C C R C C A C C C
Pseudodiaptomus coronatus C C C C C R R R RR R C C C R C C
Tortanus setacaudatus R R
Temora turbinata R R R R R R R R R
Corycaeus sp. R R R R R R R R
Oithona cotcarva CC C R C C C R C C R R C C R R C C
Saphirella sp. RR RB RR RB R R R R R R R R
Oncaea venusta R R R R R R
Euterpina acutifrons C C R R C C C R R R R R R R R R R
Other harpacticoids RR R R R BR R R C C C R R R C C
Copepod nauplii C C C C C C R C A C R R C R C C C C
Copepodids R R R R RB R C C C C R R R R RR
Meroplankton:
Coelenterate larvae R R R R R R R R R R R R R
Cyphonautes larvae(Bryozoans) R R R R R R R R R R C C R
Actinotroch larvae(Phoronida) R
Trochophore larvae R R R R R R R R
Polychaete larvae R RC C BR R B R B C R C R C
Gastropod veligers C C C C C C R R R R C R C A C C
Bivalve larvae R R R R R R R R R R R R R C R R R
Echinoderm larvae(starfish,
sea cucumber) R R R R R R R
Pluteus larvae(ophiuroids,
echinoids) R R R R
Barnacle nauplii C C C C A A C A C A C A A A C C C A
Barnacle cyprids R R R R R R R R R R R R R R C R R R
Porcellanid crab zoeae R R
Crab zoeae (other) A A C C R R R R R A A C C
Crab megalopae R R R R R R R R
Palaemonetes juveniles R R R
Shrimp larvae (other) R R R R R R R R R
Decapod larvae (other) R R R R R R R R R
Fish larvae R R R R R R R R R
Others:
Hydroid polyps R R R R R R R R
Cladocerans R R R R R R
Ostracods R R R C R R R R R R R R R R R
Mysids R R R RR R R R R R
Cumaceans R
Gammarid amphipods R R R R R R R R R R
Caprellid amphipods R R R R
Isopods RR R R R R R R R R R R R
Lucifer R R R R R
Acetes R
Chaetognaths R C R R R R R R R
Appendicularians RR R R R R R R R R R R
Others R R R R R R R RR R R R R C C
Total Zooplankton Categories 35 39 38 28 36 37 22 19 28 26 19 19 25 25 32 38 29 35

5-5

make up a large component of the meroplankton.

Among the holoplankton, members of the Class Copepoda are usually

the most common forms. There are at least 7500 species of copepods,

divided into seven orders, the most common of which are Calanoida, Har-

pactidoida and Cyclopoida. Copepods generally have short, cylindrical

bodies (Fig. 5-la); none of the species found in this study was longer

than 2 mm. They have numerous appendages which they use for feeding and

swimming. They move with short jerky motions and can maintain themselves

in the water column for short periods by extending their antennae later-

ally to prevent sinking. The four feeding types mentioned previously

(herbivores, detritivores, carnivores, omnivores) are all found in the

Copepoda.

Copepods reproduce sexually; some shed their eggs singly into the

water, but most enclose them in ovisacs containing up to 50 eggs each,

carried near the abdominal portion of the body. The eggs hatch as

nauplius larvae (Fig. 5-1b) and go through 5-6 naupliar stages (molts)

before becoming copepodids, which resemble adults but have fewer append-

ages. There are five copepodid stages before the adult, and the entire

course of development can take from one week to a year, depending upon

the species. Most free-living species have a maximum life span of 6

months to a little over I year.

Calanoids are the most characteristic group of marine holoplankton

and 14 species have been found in the North Inlet-Winyah Bay area, of

which ten (Tables 5-1 and 9-2) are fairly common (Lonsdale and Coull,

1977; Ferrell, unpublished). In particular, Acartia tonsa, Parvocalanus

5-6

I~~~~~~~~~~~~~~~~~~~

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~I'

~~~~~i.51 oolntno in a B ySC:.clnodcpod
~~~~~~~b oeo apius .otao;d ldcrn .cat
~~~~~~nahf.apniuainin t os.Saebrrpeet
I~~~~~~~. m
I~~~~~~~~~~~~~-

(Paracalanus) crassirostris and Pseudodiaptomus coronatus are character-

istic of the study area (Tables 5-1 and 9-2; Lonsdale and Coull, 1977),

as well as other estuarine and coastal environments in the east and south -

east (Bowman, 1971; Alden, 1977; Sandifer et al. 1980). Calanoids are

found throughout the world, and can be recognized by their relatively

large size, torpedo shape, and long first antennae (Fig. 5-la).

Cyclopoid copepods are a little smaller than calanoids, and have a

generally wider head region tapering towards the abdominal region. They

also have shorter first antennae. At least seven species of cyclopoids

have been identified in the North Inlet-Winyah Bay area (Lonsdale and

Coull, 1977; Ferrell, unpublished), of which Oithona colcarva, Corycaeus

sp., Saphirella sp. and Oncaea venusta are fairly regular in occurrence

(Tables 5-1 and 9-2). These genera were also common in the Cape Fear

River estuary (Copeland et al. 1974), and have been recorded previously

from North Carolina, South Carolina and Georgia waters (Sandifer et al.

1980).

Fifty-three species of harpacticoid copepods have been identified in

the Winyah Bay-North Inlet region (Coull, 1978), but most of these are

meiofaunal forms which live within or on the sediments. Although they

are an extremely important part of the benthic community, relatively few

harpacticoids occur in the plankton. Several species may spend part of

their adult life as temporary plankton (M. Palmer, unpublished), but the

most regularly occurring holoplanktonic species is Euterpina acutifrons.

Euterpina is cosmopolitan, and has been found in estuarine and coastal

waters all along the east coast and the Gulf of Mexico (Alden, 1977).

5-8

Another crustacean group which is common in the holoplankton, al-

though not nearly as abundant as copepods, are members of the Class Ostra-

coda (Fig. 5-1c). Ostracods are also called seed shrimps, and are found

in freshwater, marine, and estuarine habitats. There are approximately

2000 living species worldwide, which range in size from I to several

millimeters. Ostracods have bivalved shells, and look very similar to

small clams, except they have numerous appendages protruding from the

shell. Most species are benthic, but a few live in the water column,

feeding on detritus and phytoplankton. Although they were not identified

to species, ostracods occurred in the study area nearly year-round (Tables

5-1 and 9-2).

Cladocerans, or water fleas, are also members of the holoplankton

(Fig. 5-1d). They feed primarily on phytoplankton and protozoans, and

carry their eggs in a brood chamber. Development is direct, with no

larval forms being released into the plankton. Cladocerans are members

of the Class Branchiopoda, and are especially characteristic of fresh

waters. Nevertheless, several genera, including Podon, Evadne and

Penilia occur in nearshore and estuarine waters, and were found in this

study (Tables 5-1 and 9-42).

Several other crustacean groups are represented in plankton collec-

tions, but they were rarely captured effectively in our microzooplankton

nets. These include many small shrimps, isopods, amphipods, mysids,

cumaceans, and stomatopods. Many of these groups were captured in the

epibenthic sled collections, and their occurrence and biology are dis-

cussed in Chapter 6.

5-9

There are three commonly-occurring holoplankton groups which are

not crustaceans: chaetognaths, appendicularians, and ctenophores (see

Chapter 6). Chaetognaths, or arrowworms, are voracious predators in the

plankton, consuming up to 37% of their body weight per day (Green, 1968).

Their diet consists chiefly of copepods, but they are also known to take

larval fish. They move by combinations of swimming and floating, and

resemble feathered darts in appearance (Fig. 5-le). They are clear, and

average 3 cm or less in length. Pierce and Wass (1962) listed four spe -

cies which were common inshore, including Sagitta enflata, S. helenae,

S. hispida and S. tenuis.

Appendicularians are members of the subphylum Urochordata, Class

Larvacea. They are small (1-5 mm) soft-bodied organisms who build mucus

"houses" which contain fine-mesh filters capable of capturing bacteria-

sized particles (Fig. 5-1f). Thus, they may be extremely important in

the zooplankton food chain, passing energy from bacteria and nannoplank-

ton to higher trophic levels. Costello (1981) found that appendicularians

in the North Inlet-Winyah Bay area occur in greatest densities offshore,

with inshore abundances changing according to stage of tide and season.

Three species, Oikopleura dioica, O. longicuada and Appendicularia silcula

were found, with 0. dioica being most abundant inshore.

The meroplankton, or temporary zooplankton, consist chiefly of lar-

val stages of benthic invertebrates, and are very diverse. Meroplankton

are especially abundant in nearshore (Reeve and Baker, 1975) and estuarine

waters (Raymont, 1963; Green, 1968), and species composition may reflect

the faunal composition of adjacent estuaries or marshes (Turner et al. 1979;

Christy and Stancyk, 1981). As with holoplankton, crustaceans make up a

5-10

very large component of the meroplankton.

Among the most ubiquitous crustacean meroplankton are the larvae of

barnacles (Class Cirripedia), which are all sessile as adults. Barnacles

are extremely common in marine and estuarine subtidal and intertidal hab-

itats. Over 900 species have been described, with 30 or more occurring

in coastal South Carolina waters (Zullo and Lang, 1978). Lang (1979)

collected 11 species of barnacles in the North Inlet-Winyah Bay region,

and described the larval development of 10 of them. Barnacles release

their young from the mantle cavity as nauplii (Fig. 5-2a), characterized

by the possession of horns on the head region and their upside down swim-

ming habit. The young pass through six naupliar stages, during which

time they feed on phytoplankton, chiefly diatoms and flagellates. Some

species may be partially carnivorous, as they have been observed feeding

on weakened copepods in the laboratory (T.L. Ferrell, unpublished obser-

vations).

Prior to metamorphosis to the adult stage, barnacle nauplii go

through a cyprid stage. Cypris larvae (Fig. 5-2b) resemble ostracods

because they have a bivalved shell. They contain cement glands, and if

they find a suitable substrate, are capable of metamorphosing into the

sessile adult form. If they fail to find a suitable substrate, they may

defer settlement for varying lengths of time. Barnacle settlement may

be quite substrate-specific, and recent work (Strathmann and Branscomb,

1979; Strathmann et al. 1981) has demonstrated that settlement in the

wrong habitat can be fatal. Habitat-specific cues are often used by

settling invertebrates (Meadows and Campbell, 1972), and if their abili-

ties to sense these cues are hampered, the results can be fatal. Pearson

5-11

a - b~~~~~~~~~~

a. b. U~~~~~~~~~~~~~~r

d~~~~~~

I \..

Fig 52.MeoplnkoninWinahSa, .C. a brnclenapluU
~~~b ancl.pi;c rbze;d.hdoeua .toh
phore; f. b ~ ~ ~ ~ivlevlgr .gsrpdvlerh.oycat

5-~~~~~~~~~'12

and Olla (1979) have recently shown that hydrocarbon fractions can inhi-

bit the sensory abilities of adult crabs, and it is possible that numer-

ous larval forms could also be affected by these chemicals (Olla, person-

al communication).

Crab larvae, called zoeae (Fig. 5-2e), are among the most well-

studied and easily-recognized crustacean larvae in nearshore-estuarine

areas. Considerable work has been done on the zoeae of estuarine crabs,

particularly the commercially important blue crab, CaZZllinectes sapidus

(e.g. Sulkin et al., 1980), and the mud crab, Rithropanopeus harrisii

(e.g. Cronin and Forward, 1979). In the North Inlet area, including

South Jones and No Man's Friend Creeks, up to 95% of the crab zoeae col-

lected belong to one of the three local fiddler crabs, Uca spp. (Christy

and Stancyk, 1981; DeCoursey, 1979), although zoeae of at least 15-18

species of brachyuran crabs have also been identified (Christy, personal

communication). Because of their numerical abundance, larvae of Uca spp.

in North Inlet and elsewhere have been the subject of several studies

(Bergin, 1981; DeCoursey, 1979; Christy, 1978). Zoeae are seasonally

important predators of copepods and other small zooplankton, and molt

through 3-6 zoeal stages before changing to the pre-metamorphosis megalops

stage. Megalopae, although much smaller, have a morphology very similar

to the adult crabs (see Fig. 6-6a), except that their abdomens are not

folded under the carapace. Research on these forms indicate that mega-

lopae of estuarine crabs move into the estuary and up tidal creeks before

metamorphosis (Sandifer, 1975; Christy, personal communication). They

are distributed primarily near the bottom and are strong enough swimmers

to avoid smaller plankton nets, so they were captured more efficiently

5-13

in the epibenthic sled, and will be discussed in Chapter 6.

Larvae of many non-crustacean organisms are also commonly found in

the North Inlet-Winyah Bay plankton. Included among these are the medusa

larvae of hydrozoans (Phylum Cnidaria; Fig. 5-2d), which resemble the

larger, more well-known holoplanktonic jellyfish (Classes Scyphozoa and

Cubozoa). Hydrozoan medusae are predaceous and occur widely throughout

the system, especially in the warmer times of year.

Larvae of molluscs (especially clams and snails) and polychaete

worms are also extremely abundant in nearshore and estuarine waters.

The earliest larvae of both groups are small, yolky, ciliated trocho-

phores (Fig. 5-2e) which are capable only of the weakest swimming move-

ments. Clams (including such commercially important species as the Amer-

ican oyster, Crassostrea virginica, the Southern Quahog, Mercenaria mer-

cenaria, and the Calico Scallop, Argopecten gibbus) and snails (such as

the whelks, Busycon spp., the mud snail, Illyanassa obsoZeta, and the

tulip shell, Fasciolaria lilium) go from trochophore to veliger stages

(called bivalve and gastropod veligers IFig. 5-2f and 5-2g}, respective-

ly). Polychaete trochophores become larvae (Fig. 5-2h) which resemble

adult worms except that they have extremely long setae and are strong

swimmers. These larval stages are primarily herbivorous, and may spend

from 1 to several weeks in the plankton. Local molluscs and polychaetes

are extremely diverse, and their larvae are very difficult to distinguish

to species, so they were not classified further in this study. However,

the diversity of these groups in the area makes it unlikely that peaks

in abundance of bivalve, gastropod and polychaete larvae (Tables 5-1 and

9-2 ; Fig. 5-2 ) represent individuals of the same species.

5-14

Many other larval forms of benthic adults can be found in the

North Inlet-Winyah Bay region, These include actinotroch larvae of the

small phylum, Phoronida, pilidium larvae of nemerteans, cyphonautes lar-

vae of bryozoans, and bipinnaria or pluteus larvae of echinoderms (sea

cucumbers, starfish and brittlestars). Examples of these groups are il-

lustrated in most invertebrate textbooks (i.e.,Barnes, 1980) or plank-

ton manuals (i.e., Smith, 1977). None of these larvae are extreme-

ly abundant at any one time, but together they make up a large component

of the meroplankton. Their role in the plankton is poorly known, but if

these populations were disturbed by pollutants, the effects on the adult

populations, including the commercially important forms, could be disas-

trous.

Table 5-1 shows the species of zooplankton captured by cruise in

No Man's Friend (NMF) and South Jones (SJ) Creeks between August, 1980 and

July, 1981. Although there are 11 to 15 species of copepods and up to

27 other categories present on each cruise, only a few are dominant at

any time; 5 to 8 species usually make up over 90% of the animals by num-

ber. In general, the two creeks have the same dominant species at the

same times, but mean numbers and presence or absence of minor species may

vary. All of the 18 species of copepods which occur with regularity in

North Inlet were collected at NMF and SJ, but only two, Acartia tonsa

and Parvocalanus crassirostris, were extremely abundant; they occurred

in numbers at least one order of magnitude greater than any other cope-

pod species. Only five species of copepods were year-round residents in

the creeks (Acartia tonsa, Parvocalanus crassirostris, Pseudodiaptomus

coronatus, Oithona colcarva, Euterpina acutifrons). Along with most of

5-15

the other copepods, they were most abundant in spring and summer. On the

other hand, some copepods were distinctly winter residents. Centropages

hamatus and Eurytemora affinis, for instance, were found only between

November and April, when numbers of other copepod species were lowest.

Some non-copepod forms also showed peak winter abundance, particu-

larly nematodes. Most of the non-copepod groups were warm-season types,

however, including appendicularians, chaetognaths, and larvae. Larval

forms of benthic or pelagic species were often seasonal in appearance,

but could become dominant organisms during periods of peak abundance.

The most conmmon larval forms were barnacle nauplii, crab zoeae, cypho-

nautes larvae of bryozoans, gastropod veligers, and polychaete larvae.

Some of these groups (i.e. barnacle nauplii, barnacle cyprids, and poly-

chaete larvae) were present throughout the year, which probably indicates

reproduction by several species during that time.

I. HOLOPLANKTON

A. Acartia tonsa,

As in many other eastern estuaries from Cape Cod to western Flori-

da (Woodmansee, 1958), this species dominates the North Inlet-Winyah

Bay ecosystem. In NMF and SJ, A. tonsa reached mean abundances of 5-

6000/m3 , and formed a co-dominance during the spring and summer with

Parvocalanus crassirostris (Fig. 5-3). A. tonsa abundance was usually

greater in NMF than in SJ, but seasonal trends were exactly the same.

Acartia copepodids (Fig. 5-3) followed similar trends, and together

with adult A. tonsa they dominate the system by an order of magnitude

when present. Acartia shows considerable seasonal variation, however,

5-16

ACARTIA TONSA

7200 * Adults
0 Copepodids

4800-

z 2400-

Cruise I 3 5 7 9 1 1 13 15 17
Month A S S 0 N N D J J F M M A M J J J A

7200 -

1: 4800;

Z 2400

O. . . . . . . . . . . . . . . . .
Cruise 1 3 5 7 9 1II 13 15 17
Month A S S 0 N N D J J F M M A M J J J A

Figure 5-3. Mean densities (no./m3) of adult and copepodid Acartia tonsa
on cruises 1 - 18 at NMF (above) and SJ (below). Vertical
lines indicate plus or minus the standard error.

5-17

and is nearly absent from both creeks during the winter months (Oct-

ober-March).

Acartia tonsa is a warm-water euryhaline species. It occurs in the

northern part of its range only in the summer (Jeffries, 1962; Durbin

and Durbin, 1981), although it is a year-round resident in Florida

(Woodmansee, 1958) and North Carolina (Sutcliffe, 1948). Adults mea-

sure from 1.0-1.5 mm in length, and females have two broods (Deevey,

1948). They may go through several generations (about 37 days from

egg to adult; Jeffries, 1962) in a season, and up to 11 generations

a year (Woodmansee, 1958). A. tonsa is a true estuarine species (Bow-

man, 1971) with a broad salt tolerance range (Lance, 1963). It is

generally found in greater numbers in bays and rivers than more open

waters (Grice, 1960; Sandifer et al., 1981). In North Inlet, popula-

tions of A. tonsa were not significantly flushed from the estuary

(Stancyk and Ferrell, unpublished); and in other estuaries have been

shown to be distributed in the water column in a manner which favors

retention in estuaries (Show, 1980). Trinast (1975) found that an-

other Acartia species in a California estuary was also retained. A.

tonsa is a fairly generalized feeder, and has been shown in the labo-

ratory to consume phytoplankton, detritus, and larvae of other cope-

pods (Lonsdale, Heinle, and Siegfried, 1978; Heinle, Harris, Ustach

and Flemmer, 1977). In fact, its abundance during certain parts of

the year, coupled with its predatory habits, may prevent less common,

smaller copepod species populations from growing during the warm sea-

sons (Lonsdale et al., 1978).

Lonsdale and Coull (1977) demonstrated an Acartia tonsa - Parvocala-

nus crassirostris codominance in the warm months in North Inlet; they

also demonstrated that although the smaller ParvocaZanus was more

abundant year-round, A. tonsa dominated in biomass. This species is

one of the most important copepods in the nearshore system. It is

fed upon by numerous fishes (Allen et al.,1978; Durbin and Durbin,1981)

and is extremely productive when it is present. Perturbations which

remove A. tonsa from the system when it normally would be present

would have significant effects on the rest of the ecosystem by re-

moving a species which plays a central role in the zooplankton com-

munity.

B. Parvocalanus crassirostris

This species was the most abundant copepod year-round at SJ and

NMF (Fig. 5-4). Although there were sampling periods when P. crassi-

rostris numbers were quite low, there was no evidence of seasonality

in the occurrence of this species. On many occasions, mean numbers

would exceed those of Acartia tonsa, but Lonsdale and Coull (1977)

demonstrated that A. tonsa, being larger dominated in biomass on an

annual basis at North Inlet, and the relationship appears to hold at

SJ and NMF. The numbers of P. crassirostris on any given sampling

date were usually lower at SJ than at NMF (Fig. 5-4), but they usually

showed peaks of abundance at the same times. An exception to this oc-

curred in early June, 1981, however, when Parvocalanus numbers ranged

around 3200/m3 at NMF, but were only about 600/m3 at SJ. Numbers sub-

sequently declined at NMF, and by July the stations were once again

similar.

Parvocalanus crassirostris is not as widespread as Acartia tonsa,

5-19.

PARVOCALANUS CRASSIROSTRIS

3600-

2400 -
o I w t %

Cruise 1 3 5 7 9 1 13 15 1
Month A S S 0 N N J J F M M A M J J J A

E 400
1200- It
I
~i I

o I

Month A S S 0 N N D J J F M M A M J J J A
iI

Monthcruises 1 - 18 at N N D F M M A M J d J AVertical
24005-20

C,[
I I

Z 1200 �
,. ;.'

Cruise I 5 5 7 9 II 13 15 17
Month A S S 0 N N D J J F M M A M J J J A

Figure 5-4. Mean densities (no./m3) of Parvocalanus crassirostris on
cruises 1 - 18 at NMF (above) and SJ (below). Vertical
lines indicate plus or minus the standard error.

5-20

but is just as characteristic of estuarine waters. It is a distinct-

ly coastal species, and is generally found where salinities range from

about 24-37 o/oo. Most published information on P. crassirostris

deals with populations sizes and distribution. It is among the dom-

inant species in many nearshore or estuarine surveys from North Inlet

to the Gulf Coast of Florida (Grice, 1960; Stickney and Knowles, 1976;

Alden, 1977; Lonsdale and Coull, 1977). It was not abundant, however,

in the Wando River in South Carolina (Sandifer et al. 1980), although

its smaller size may have made its capture less likely by the nets

used in that study. rt is chiefly herbivorous, although not much is

known about its feeding biology in the field. Although little is known

of its biology other than distribution and salinity tolerance, its a-

bundance insures that it is a large component of the diet of larval

fishes and larger carnivorous crustacean larvae.

C. Pseudodiaptomus coronatus

This was the third most abundant calanoid copepod in the areas sam-
3
pled (Fig. 5-5) but rarely reached numbers as high as 2700/m . Mean

abundances were closer to 400/mi, and Pseudodiaptomus was found in

spring, summer and fall, when its abundance was greatest. Numbers

were usually higher at NMF, but as with other species, peaks usually

coincided between the two creeks. Pseudodiaptomus occurred at NMF as

late as November, but was not found at SJ after early October.

Although is it quite widespread (Nova Scotia to Mississippi River;

Wilson, 1932; Wright, 1936) and is characteristic of temperate marine

or brackish water, P. coronatus is never as abundant as the aforemen-

tioned species. In the southern part of its range, it Is more of a

5-21

PSEUDODIAPTOMUS CORONATUS

1200 '

I
800-
o I

Z400

I I \ I

Cruise I 3 5 7 9 1I 13 15 17
Month A S S 0 N N D J J F M M A M J J J A

1 200 .

800

400

I . . . . . . . . . . . . . . . .

Cruise I 3 5 7 9 1I 13 15 17
Month A S S 0 N N D J J F M M A M J J J A

Figure 5-5. Mean densities (no./m3) of Pseudodiaptomus coronatus on
cruises 1 - 18 at NMF (above) and SJ (below). Vertical
lines indicate plus or minus the standard error.

5-22

fall-winter species, but has peak abundances in spring and especially

fall in other areas (Sutcliffe, 1948; Woodmansee, 1958; Sandifer et al.,

1980). Its occurrence at SJ and NMF Creeks was different than in the

mouth of North Inlet in 1975 (Lonsdale and Coull, 1977) when it had

high densities from late winter through the summer.

Pseudodiaptomus coronatus is a relatively large (1.0-1.5 mm) species,

which Jacobs (1961) contended was not truly planktonic, since it clung

to detritus and other suspended material. Such abilities would allow

it to modify its vertical and horizontal distribution, and Jacobs, in

fact, found greatest concentrations of P. eoronatus copepodites near

the bottom in Doboy Sound and the Duplin River in Georgia. Such a

distribution would make the species less likely to be exported from

estuarine situations, and possibly more susceptible to bottom preda-

tors or to environmental hazards such as pollutants stirred from bot-

tom sediments.

D. Centropages hamatus

This was the most common of three species of Centropages in the

area, including C. hmnatus, C. furcatus, and C. typicus. Although

it was never as abundant as the calanoids previously mentioned, C.

hcmatus is distinctive in that it was a definite winter resident at

SJ and NMF (Fig. 5-6). Even in winter, its occurrence was relatively

patchy, with peaks occurring in November, February, and April at SJ,

but only in February and April at NMF. Abundances were never as high

at NMF as SJ, which is opposite from the calanoids described above.

Centropages hamatus is a robust copepod 0.9-1.35 mm in size. rts

5-23

CENTROPAGES HAMATUS

400 -

E
0

Cruise 1 3 5 7 9 1 1 13 15 17
Month A S S 0 N N D J J F M M A M J J J A

600-

I 400'

z 200
a'
I !

Cruise I 3 5 7 9 1I 13 15 17
Month A S S 0 N N D J J F M M A M J J J A

Figure 5-6. Mean densities (no./m3) of Centropages hcmatus on cruises
1 - 18 at NMF (above) and SJ (below). Vertical lines
indicate plus or minus the standard error.

5-24

range is from the Chesapeake Bay to the Gulf coast of Florida (Wilson,

1932; Grice, 1960). It appears to be primarily herbivorous in nature

(Smith, 1975; from Alden, 1977), with a winter occurrence throughout

its range. Wilson (1932) suggested that C. hamatus is probably eaten

by shad during their spring migrations, and it was one of the most

abundant copepods found in the guts of larval fishes in North Caro-

lina estuaries (Thayer et al., 1974),

E. Oithona colcarva

This small cyclopoid copepod was the third most abundant form in

the study (Fig. 5-7). As found by Lonsdale and Coull (1977), it oc-

curred in lower numbers in spring, and had its highest density in

late fall, with a peak mean of 3720/m3 in November, 1980. Numbers of

animals were generally similar between NMF and SJ, and peaks of abun-

dance coincided exactly. Oithona is smaller than the species previ-

ously discussed, but it is also characteristic of estuarine situations

(Wilson, 1932). It has a wide distribution from Cape Cod to the Texas

Coast (Bowman, 1975) and may breed year-round, at least in Florida

waters (Grice, 1960). It may be one of the species whose abundance

is reduced when Acartia tonsa is abundant due to predation on Oithona

larvae by adults of the calanoid (Lonsdale et. al. 1978).

F. Euterpina acutifrons

Although several other harpacticoids occur incidentally in the

plankton, Euterpina is the only species usually considered to be pe-

lagic (Lonsdale and Coull, 1977; D'Apolito and Stancyk, 1979) and it

was the most abundant harpacticoid in the water column in this study.

It was present at all times of year at NMF and SJ except January and

5-25

OITHONA COLCARVA

I I

E 2400.
._ II

z 1200

o. I ,,
OI_--'/ � "1

Cruise I 3 5 7 9 1 13 15 17
Month A S S 0 N N D J J F M M A M J J J A

3600

2400'

) o

0I IIj

t. I
"',.I I
z 1I200 ---. '|

', . ' I ;

Cruise 1 3 5 7 9 II 13 15 17
Month A S S O N N D d J F M M A M J J J A

Figure 5-7. Mean densities (no./m3) of Oithona colcorva on cruises
1 - 18 at NMF (above) and SJ (below). Vertical lines
indicate plus or minus the standard error.

5-26

EUTERPINA ACUTIFRONS

720 �

1 480-

E I r
240 I
k \ I I

.. .V

. . . . . . . . . . . . . . . . .
Cruise I 3 5 7 9 1 I1 13 15 17
Month A S S 0 N N 0 J J F M M A M d J J A

720

: 480

I I %
240 %

. . . . . . . . . ...p- . . ...

Cruise 3 5 7 9 I 11 3 15 17
Month A S S 0 N N D J J F M M A M J J J A

Figure 5-8. Mean densities (no./m3) of Euterpina acutifrons on cruises
1 - 18 at NMF (above) and SJ (below). Vertical lines
indicate plus or minus the standard error.

5-27

February (Fig. 5-8), with large peaks in both creeks in November. Abun-

dances were generally similar between the two creeks. The year-round

occurrence corresponds to findings in North Inlet by Lonsdale and

Coull (1977), but they found peaks of abundance in the summer and

early fall. D'Apolito and Stancyk (1979) found E. acutifrons in North

Inlet only from April through December in 1977.

E. acutifrons has a worldwide distribution in coastal, shelf and

estuarine waters (Fanta, 1972), and is known to breed only in the

warmer times of year (at least 11�C; optimal in North Inlet, 16.5�C;

D'Apolito and Stancyk, 1979). The species is unusual in that males

are dimorphic and occur in the population simultaneously. Some au-

thors (i.e., Moreira and Vernberg, 1968) have suggested that the two

different types of males have different temperature-salinity toler-

ances, while others (Haq, 1973) have hypothesized that they breed

with females in different frequencies or different times of year. In

any case, the abundance of Euterpina in estuarine waters, together

with its relatively small and delicate form (0.5 - 1.0 mm) make it

prime food for larval fishes, and Kielson et al. (1975) found it to

be one of the dominant food items in the guts of menhaden (Brevoortia

tyrannus), pinfish (Lagodon rhomboides) and spot (Leiostomus xanthurus)

in the Newport River estuary, North Carolina.

G. Chaetognaths

Next to ctenophores, chaetognaths are probably the most voracious

invertebrate predators of the zooplankton in the estuary. At NMF and

SJ, their abundance was extremely seasonal (Fig. 5-9), with highest

5-28

192- CHAETOGNATHS

128-

Cruise I 3 5 7 9 1II 13 15 17
Month A S S O N N D J J F M M A M J J J A

1 92

I
128-
- !

ID I I
, !
Z 64

o . . . . .. . . .- . . . . . . . . . .

Cruise 3 5 7 9 151 13 15 17
Month A S S 0 N N D J J F M M A M J J J A

Figure 5-9. Mean densities (no./m3) of chaetognaths in zooplankton
collections on cruises 1 - 18 at NMF (above) and SJ (below).
Vertical lines indicate plus or minus the standard error.

5-29

24- CHAETOGNATHS

.z=,
. 1..
~40,. h

�2
08 \ S_,' '" - - - - - - - m

... . . . . . . . . . . . . . . .
Cruise I 3 5 7 9 1 1 13 15 1 7
Month AS S S N N DJ J F M M A M J J J A

I
6405

I ;
- i
E ,
Z 20' , ' jI

Cruise I 3 5 7 9 11 13 15 17
Month A S S 0 N N D J J F M M A M J J J A

Figure 5-10. Mean densities (no./m3) of chaetognaths in epibenthic sled
collections on cruises 1 - 18 at NMF (above) and SJ (below).
Vertical lines indicate plus or minus the standard error.

5-30

numbers in the summer, especially July and August. Numbers were simi-

lar between the two creeks, although chaetognaths were slightly more

abundant at SJ in August of both 1980 and 1981. Since chaetognaths

were captured in both zooplankton nets and the epibenthic sled, com-

parisons between the two methods of capture can be made. Figure 5-10

shows the numbers of chaetognaths captured in the sled, and the peaks

of abundance correspond exactly with the zooplankton data (Fig. 5-9);

however, estimates of numbers/m3 are 2-3 times lower in the sleds.

This could be because sleds capture chaetognaths less efficiently

than nets, or because chaetognaths were actually more abundant in sur-

face waters. Further sampling is being performed in Winyah Bay.

H. Appendicularians

These soft-bodied organisms, chiefly in the genus Oikopleura, are

fairly common in nearshore coastal waters (Costello, 1981). They are

much less abundant in estuaries, however, and occurred at NMF and SJ

Creeks only sporadically (Fig. 5-11). They were most abundant in the

spring and summer months, reaching densities uD to 120/m3. Such den-

sities are low compared to counts as high as 20,000/m3 made by Costel-

lo (1981) in nearshore South Carolina waters. Costello also found

that appendicularians were generally swept into North Inlet, so the

highest densities at any up-estuary station occurred at the highest

tides. Inshore densities dropped precipitously, especially at low

tide periods, so the small numbers of appendicularians found at NMF

and SJ is not surprising. The unusual peak at NMF in September, 1980,

and at South Jbnes in November, 1980, are probably due to significant

input of coastal water masses at these times, and illustrate the way

the occurrence of this species is closely tied to water flows.

5-31

APPENDICULARIANS
1 80

: 120 -

.o I ;

* t I g

. . . . . . . . . . . . . . . . ...
Cruise I 3 5 7 9 1 1 13 15 17
Month A S S 0 N N D J J F M M A M J J J A

~ :o

* __./ \ . -t/-

Cruise I 3 5 7 9 II 13 15 17
Month A S S 0 N N D J J F M M A M J J J A

Figure 5-11. Mean densities (no./m3) of appendicularians on cruises
1 - 18 at NMF (above) and SJ (below). Vertical lines
indicate plus or minus the standard error.

5-32

Alldredge (1972, 1976) studied the importance of appendicularians

and their houses in the Gulf Stream and Gulf of California. She

cited numerous instances of calanoid and cyclopoid copepods, as well

as several other forms of crustaceans, which rested on, rode in, or

fed upon discarded mucus houses of appendicularians. Houses were

built and discarded at a rapid rate (up to 6 times per day), and the

rate was proportional to the amount of particulate material in the

water. Since estuarine waters have high amounts of particulates,

house production by the appendicularians in the Winyah Bay system is

probably high. Thus, appendicularians may provide material for con-

sumers not only as food items themselves, but also in the form of

mucus houses which have often captured large amounts of phytoplankton,

bacteria or fine detritus. Their role in the estuarine plankton may

be masked by their low numbers, and studies by Stancyk and Ferrell

(unpublished) indicate that these are the only adult zooplankton forms

significantly imported into North Inlet. The role of mucus houses as

a nutritional source, as well as a means of concentrating man-made or

natural substances and passing them up the food chain, requires con-

siderably more study (Alden, 1977).

I I.MEROPLANKTON

The general meroplanktonic forms found in the Winyah Bay system and

some aspects of their biology were discussed earlier in this chapter; the

following section will deal only with the more abundant forms, and will

emphasize specific sampling results at No Man's Friend and South Jones

Creeks.

5-33

Barnacle nauplii were by far the most abundant larvae in the Winyah

Bay zooplankton samples (Fig. 5-12), reaching peaks as high as 2100/m3.

They were present year round in both stations, with peak abundances in

the fall (October) and spring. Peaks are especially clear at NMF, where

between-peak densities were generally lower than at SJ. Abundance of

barnacle nauplii at SJ was relatively high year round, averaging about

1200/m3 versus about 600/m3 for NMF. Barnacle nauplii are one of the

few forms which show dramatic differences between the two creeks, and

these could be due to many causes, including different numbers of adults

in the two creeks to supply larvae to the overlying water column or more

nauplii in nearshore coastal waters. In addition, there are almost cer-

tainly several species of barnacles producing larvae (Lang, 1979) which

could lead to variations in barnacle nauplius numbers in both space and

time due to variations in adult distribution. In any case, barnacle

nauplii dominated the plankton from December through April, which is in

marked contrast to North Inlet proper, where Lonsdale and Coull (1977)

found highest densities of barnacle nauplii between April and August.

The more advanced stages of larval barnacles, the cyprids, were much

rarer and more seasonal than the nauplii (Fig. 5-13). Densities of these

forms were about an order of magnitude lower than the nauplii, and peaks

occurred only during the months of January and June-July. There were

only slight differences between the creeks, with SJ having slightly high-

er numbers, especially during peaks. As stated earlier, cyprid stages

are the premetamorphosis forms, and the reduction of abundance could be

due to more disjunct distributions, with cyprids generally occurring near

the substrates (i.e., pilings, bottoms) on which they will ultimately

5-34

BARNACLE NAUPLII
3600-

2400 ,
~~~~o 18~%

I ',/

0 -
Cruise 1 3 5 7 9 1 1 13 15 17
Month A S S 0 N N D J J F M M A M J J J A

3600-

Cruise 1 3 5 7 9 11 13 15 17
Month A S S 0 N N D J J F M M A M J J JA
Figure 5-12 Mean densities (no of barnacle nauplii on cruises

200' - 'IS' 1

Cruise 3 5 7 9 " 3 15 "7

Figure 5-12. Mean densities (no./m3) of barnacle nauplii on cruises
1 - 18 at NMF (above) and SJ (below). Vertical lines
indicate plus or minus the standard error.

5-35
I~~~~~~~~~~~~~~~~~~~,:

BARNACLE CYPRIDS
240

160

Cruise 1 3 5 7 9 11 13 15 17

Cruise=~~ I ' 1,3 II
z 80 3

Cruise I 3 5 7 9 II 13 15 17

Month A S S 0 N N D J J F M M A M J J J A

Figure 5-13. Mean densities (no./m3) of barnacle cyprids on cruises
1 - 18 at NMF (above) and SJ (below). Vertical lines
indicate plus or minus the standard error.

5-36

settle. Their larger size and greater weight would also tend to keep

them near the bottom, where they would be less accessible to plankton

nets. There is no obvious correlation between barnacle nauplius and cy-

prid abundance in either creek, although cyprid peaks tend to occur at

times when nauplii are in lower abundance (Fig. 5-12 and 5-13).

Crab zoeae are extremely abundant in both creeks, but only at very

specific times (Fig. 5-14). Previous studies have shown that the major-

ity of the zoeae in the tidal creeks of North Inlet are Uca spp., the

larvae of fiddler crabs (DeCoursey, 1979; Christy and Stancyk, 1981).

These larvae are all in the early stages of development (stages 1-3),

and are released by their ovigerous female crabs at the time of highest

nighttime spring tides during the spring and summer months (Bergin, 1981;

Christy and Stancyk, 1981). The fact that crab zoeae show peaks only

during one August and one June sample is due to sampling, and does not

reflect annual zoeal production in these areas. Samples taken at times

not within 3 days of maximum spring tides yield very few zoeae, because

they have apparently been flushed from the system (Christy and Stancyk,

1981). Calculations performed on measurements of zoeal flux from North

Inlet, for example, indicate that all zoeae entrained in the water pas-

sing back and forth across the inlet mouth would be exported within 7

tidal cycles. Earlier studies by Stancyk and Ferrell (unpublished) re-

vealed that the response of zoeae to changes in direction of tide were

much higher at SJ than at the mouth of North Inlet, indicating a greater

tendency to be washed from the system in the southern creeks. The ab-

sence of zoeae in the non-spring tide summertime samples tends to rein-

force these findings, and leads to the conclusion that while zoeal pro-

5-3.7

CRAB ZOEA

6600 -

'I
4400- i
I

Z 2200 -

tI I

\ // \ I _CI--
O - --_--- --- ---_---_--_----_ ,___

Cruise 1 3 5 7 9 II 13 15 17
Month A S S 0 N N D J J F M M A M J J J A

6600

4400 1

= . I I I

z 2200-
I '
I s I

0- L-, ; - -,,___ ~,,.

5-38 ....
Cruise 1 3 5 7 9 1 1 13 15 17
Month A S S 0 N N D J J F M M A M J J J A

Figure 5-14. Mean densities (no./m3) of crab zoeae on cruises 1 - 18
at NMF (above) and SJ (below). Vertical lines indicate
plus or minus the standard error.

5-38

duction near nighttime spring tides may be quite high (over 5000/m3) in

southern creeks, zoeal export is sufficiently rapid to remove them quite

quickly.

Finally, molluscan larvae showed distinct peaks of abundance at NMF

and SJ Creeks. Bivalves (Fig. 5-15) had the strongest peak in early

June, but also showed a distinct fall peak in late November. In both

cases, numbers of bivalve larvae were small compared to most other forms,

with 'peaks' of as few as 20 individuals/m3. Gastropod larvae (Fig. 5-16)

were more abundant, but also showed spring and fall peaks. The early

June peak at South Jones was exceptional, and gastropod veligers domi-

nated the samples at this time. This peak, which also occurs in several

other forms (see Fig. 5-3,4,5,10,11,13, and 14), occurs on a nighttime

spring tide when the water temperatures first approach 250C, and may mark

a time of extremely high spawning activity amona invertebrates in the

system. There was a strong difference in abundance of veligers between

SJ and NMF Creeks at this time, which could be due to differences in

water masses or in the number of spawning adults in the two areas.

In summary, the zooplankton in South Jones and No Man's Friend Creeks

is similar to that found in North Inlet (Lonsdale and Coull, 1977; Stan-

cyk and Ferrell, unpublished) and other southeastern estuaries (Alden,

1977; Sandifer et al. 1980), but there are distinct differences in abun-
dances and times of occurrence between areas. The most common species are

generally widespread, but are more closely associated with warm waters

than boreal, and are therefore thought to have affinities with Caribbean

fauna (Sandifer et al. 1980). Numbers of species are relatively high,

but diversity is limited due to the fact that most systems are dominated

5-39

BIVALVE LARVAE

120-

> 40-
o- �,,,,k~ ,,,,,,,,;

Cruise 3 5 7 9 13 15 17
Month A S S 0 N N D J J F M M A M J J J A

120 -
,, 80
�) I

E I
1 20

Q 80 -

Cruise I 3 5 7 9 1 1 13 15 17
Month A S S 0 N N D J J F M M A M J J J A

Figure 5-15. Mean densities (no./m3) of bivalve larvae on cruises
1 - 18 at NMF (above) and SJ (below). Vertical lines
indicate plus or minus the standard error.

5-40

GASTROPOD VELIGERS
6000 -

1 4000-

I. .
Z 2000

Cruise 3 5 7 9 11 13 15 17
Month A S S 0 N N D J J F M M A M J J J A

6000

i 4000 e

Cruise 1 3 5 7 9 1 13 15 17
Month A S S 0 N N D J J F M M A M J J J A

Figure 5-16. Mean densities (no./m3) of gastropod veligers on cruises
1 - 18 at NMF (above) and SJ (below). Vertical lines
indicate plus or minus the standard error.

5-41

by 4-7 categories or species. In general, production is higher in the

spring and fall, with larval production occurring throughout the spring,

summer and fall. Larval forms in the creeks can sometimes dominate the

zooplankton and are usually common, but they are derived from a variety

of adult forms whose distributions and numbers are not well-known. Many

of the Winyah Bay zooplankton have been shown to provide food for other

species, particularly larval fish and crustaceans (Thayer et al., 1974;

Alden, 1977). Relatively few studies have been performed which shed light on

the effect of human activities on zooplankton (see Chapter 10), but the

general conclusions are that zooplankton communities (at least the cope-

pods) can recover from perturbations like floating oil relatively quick-

ly. Greater dangers come when negative impacts on the zooplankton re-

sult in toxic or harmful substances being passed up the food chain through

the zooplankton, or in reduced recruitment into benthic invertebrate,

crustacean or fish populations. Such phenomena usually occur slowly and

are difficult to detect, but often have significant long-term impacts. In

any case, the diversity and complexity of the zooplankton reinforces the

concept that these organisms interact with, and have an impact on, many

other parts of the estuarine-coastal ecosystem. Until more is learned

about these connections and the role of the zooplankton, potential negative

impacts on the community should be avoided.

5-42

CHAPTER 6. MOTILE EPIBENTHOS

The size, behavior, and microhabitats of subtidal estuarine organ-

isms determine their susceptibility to collection in nets. Copepods and

other weak-swimming zooplankton, less than 2 mm in length, are usually

dispersed in the water column and are effectively sampled with plankton

nets. Many other small (2-20 mm) invertebrates and larval fishes are

undersampled by zooplankton nets because: (1) they are accomplished swim-

mers which can avoid slowly towed nets and (2) most have a strong affin-

ity for the bottom. Such organisms are referred to as motile epibenthos.

In the study of No Man's Friend (NMF) and South Jones (SJ) Creeks, a

special type of sampling gear, an epibenthic sled, was used to determine

the distribution and abundance of these organisms. The design and use

of the sled were discussed in Chapter 2.

Motile epibenthic organisms may be either permanent ('holo') or tempo-

rary ('mero') members of the near bottom fauna. Permanent forms such as

mysids, amphipods, and isopods usually occur within a few centimeters of

the bottom, and, despite their abundance, they are rarely collected with

bottom dredges, grabs, and trawls. Sampling devices other than sleds

are equally ineffective in collecting late larval stages of decapod crus-

taceans and fishes which live near the bottom. Sometimes 'mero' forms to-

tally dominate epibenthic sled collections.

6-1

The taxonomic composition and abundance of organisms in sled col-

lections are highly variable. Swimming forms often aggregate and patchy

distributions account for large differences in the abundance of certain

species between consecutive sled tows. Some motile epibenthic species

occur near the bottom only under certain environmental conditions (e.g.,

temperature, light, current velocity). Species closely associated with

the substrate may be collected only over particular bottom types.

More than 700 epibenthic sled samples were collected, processed,

and analyzed to provide information on the life history strategies and

spatial and temporal distributions of motile epibenthic organisms at NMF

and SJ. The results of the study are organized into nine sections, each

describing the ecology of a major group of organisms. In the final sec-

tion, trends in total organism abundance and distribution are discussed.

A. PERICARID CRUSTACEANS

The pericarids are a diverse group of small (generally less than

20 mm) shrimp-like and crab-like animals which raise their young in

brood pouches rather than releasing larval stages into the water column.

Most estuarine pericarids are 'holo' members of the near bottom fauna.

Mysid or opossum shrimp (Fig. 6-1a) are often the most abundant epi-

benthic crustaceans in shallow water sled collections. Of the 780 spe-

cies of mysids known in the world (Mauchline, 1980), seven have been iden-

tified from the North Inlet and Winyah Bay area. Neomysis conericana is

by far the most abundant mysid in this region, and it is probably the

most common shallow water mysid in the western North Atlantic Ocean (Wig-

6-2

I ,.b.

* d.

Figure 6-1. Pericaridan Crustaceans; generalized forms of a: a. mysid
shrimp (10 mm); b. gammarid amphipod (5 mm); c. caprellid
amphipod (6 mm); d. isopod (6 mm); e. cumacean (5 mm)

6-3

ley and Burns, 1971). Other mysids which have occurred in sled collec-

tions in the study area are: Mysidopsis bigelowi, Mysidopsis bahia, Meta-

mysidopsis swifti, Promysis atlantica, Brasilomysis castroi, and Hetero-

mysis formosa (Allen, unpublished).

Female mysid shrimps brood up to fifty young in a brood pouch lo-

cated between their thoracic appendages. Young mysids which are released

from the pouch resemble adults. Adult size is usually reached in two or

three months; however, growth rates and longevities depend on environ-

mental conditions. Mauchline (1980) described the life history pattern

of many species of mysids. Details of the life cycle of Neomysis ameri-

cana have been discussed by Herman (1962), Hopkins (1965), Allen (1978),

and Pezzack and Corey (1979).

Mysids have a strong affinity for the bottom, and it is unusual to

collect mysids high in the water column, especially during the day. Al-

though the nocturnal vertical migration of mysids in coastal waters has

been well documented (e.g., Herman, 1963), most mysids in tidal creeks

remain near the bottom under all light conditions (Allen, unpublished).

Mysids feed on concentrations of microscopic algae and organic particles

near the bottom (Baldo-Kost and Knight, 1975), but also prey on zooplank-

ton (Cooper and Goldman, 1980).

Mysids were consistently more abundant in SJ than NMF Creek (Fig.

6-2). On major cruises SJ densities were often at least twice as high.

The seasonal pattern of abundance was similar at both creeks. NVeomysis

americana, which accounted for more than 95% of all mysids collected,

occurred in very low numbers in summer. Densities increased in the fall

6-4

24 MYSIDS

: 16

I ; 8

Cruise I 3 5 7 9 I1 13 15 17
Month A S S 0 N N D J J F M M A M J J J A

24 '

~~~~~~~~16~~ '

I\
I 8

,. i .

Cruise 1 3 5 7 9 11 13 15 17
Month A S S O N N D J J F M M A M J J J A

Figure 6-2. Mean densities (no./m3) of mysid shrimps in epibenthic sled
collections on cruises 1 - 18 at NMF (above) and SJ (below).
Vertical lines indicate plus or minus the standard error.

6-5

to a winter peak, then decreased to low levels the following summer (Fig.

6-2 and Table 6-1). Winter sled collections in $J often yielded thou-

sands of adult mysids per tow.

The largest mysids of the year occurred from January through March.

In early spring, large overwintering adults became reproductively active,

brooded and released their young, then di'ed. Young mysids dominated the

population in April and May, but disappeared from collections shortly

after the peak spring brood release. Predation by larval and juvenile

fishes and the migration of mysids to other sections of the estuary may

have accounted for the warm-water reductions in mysid densities. Large

winter populations of Neomysis americana in the creeks probably resulted

from migrations from adjacent coastal areas.

Although mysids are not as abundant in southern temperate and trop-

ical estuaries as they are in marshes north of Cape Hatteras (Allen, un-

published), they play an important ecological role in local estuarine

waters. Mysids are major sources of food for a variety of young estua-

rine fishes, particularly from fall through spring when larval decapod

crustaceans and other 'mero' forms are not available.

Amphipods comprise another abundant group of pericarid crustaceans.

Unlike mysids, which usually swim just above the bottom, amphipods typi-

cally remain close to sessile benthic organisms and bottom debris. Some

species live in burrows or build tube-like shelters on the bottom. Be-

cause of their secretive habits, amphipods are generally not effectively

sampled with an epibenthic sled. Amphipod distributions are patchy and

the numbers collected may Vary by a factor of 100 or more between conse-

6-6

Table 6-1. Percent composition of organisms in epibenthic sled collections on major cruises at
No Man's Friend (NF) and South Jones (SJ) Creeks. Values (based on mean densities)
represent the proportion of the total catch which each category comprises.

CRUISE NO. I 3 5 7 9 11 13 15 17
MONTH AUG SEP NOV DEC JAN MAR APR JUN JUL
CREEK NF SJ NF SJ NF SJ NF SJ NF SJ NF SJ NF SJ NF SJ NF SJ

Mysids 1 <1 4 27 15 34 42 80 64 87 74 72 66 83 2 2 I 20

Amphipods 2 <1 2 <1 6 12 7 3 9 5 i 3 2 2 <1 i 5 10

Cumaceans <1 <1 3 3 6 I 16 3 1 2 <1 I <1 <1 <1 <1 5 t

tsopods i <1 I I <1 I I 1 <1 <1 1 1 0 <1 <1 <1 <1 3

Shrimp Larvae 17 7 15 9 4 5 <1 <1 <1 0 i <1 <1 2 7 2 15 30

Other Dec. Shrimp 11 15 2 6 16 15 3 3 4 2 6 8 9 I 2 10 6 0

Crab Megalopae t8 13 40 31 25 13 5 2 0 0 0 0 <1 <1 33 58 2 <1

Chaetognaths 46 60 32 21 20 15 16 4 15 <1 2 <1 9 <1 44 13 8 28

Fish Larvae 2 3 I 2 8 3 8 3 4 2 14 13 8 3 10 13
48 7

Others 2 i <1 <1 <1 1 2 1 3 I i 2 5 8 I i
10 <1

cutive tows. Highest densities occur when the sled disrupts large sponges

or oyster shell clusters which shelter local concentrations of amphipods.

The taxonomy or scientific classification of amphipods is notorious-

ly difficult. Two suborders account for the majority of species in coast-

al South Carolina waters. Suborder Gammaridea is represented by more than

250 species, and at least 11 species from the suborder Caprellidae have

been recorded in state waters (Fox, 1978). It was beyond the scope of

this project to identify all species collected; however, gammarids (Fig.

6-1b) of the genera Melita, Monoculodes, Batea, and Gammarus and caprel-

lids (Fig. 6-1c) of the genus CapreZZa were most common. Major taxonomic

references for the amphipods of this region are: Barnard (1969), Bous-

field (1973), and Fox and Bynum (1975).

The life history patterns of gammarid and caprellid amphipods are

similar to those of mysids. Young are brooded in a marsupium and released

as miniature adults. Aspects of the reproductive ecology of some gamma-

rids have been studied by Van Dolah (1978), Borowsky (1980), Van Dolah

and Bird (1980), and Hastings (1981). Population structures of caprellids

have been reported by Caine (1979).

Gammarid amphipods were collected on every cruise, but densities were

usually less than 2/m3 in sled collections at NMF and SJ (Table 6-2).

Densities were generally higher at SJ. No pattern in the fluctuation of

abundance between cruises was apparent.

Caprellid amphipods were always less abundant than gammarids (Table

6-2). There was a strong correlation between the abundance of caprellids

and the volume of hydrozoans and bryozoans in sled collections which is

6-8

Table 6-2. Mean densities of pericarid crustaceans expressed as the
number of organisms per cubic meter of water filtered. Ab-
breviations are NF = No Man's Friend Creek, SJ = South
Jones Creek.

GAMMARIDS CAPRELLIDS CUMACEANS ISOPODS
CRUISE MONTH NF SJ NF SJ NF Si NF SJ

1 AUG 1.0 0.5 0.2 <0.1 0.1 <0.1 0.3 0.3

1 3 SEP 0.3 0.2 0.2 0.1 0.4 0.6 0.2 0.2

3 5 NOV 0.2 0.6 0 0.1 0.2 0.1 <0.1 0.1

1 7 DEC 0.1 0.1 <0.1 <0.1 0.3 0.2 <0.1 <0.1

9 JAN 0.8 1.3 <0.1 0.1 0.1 0.7 <0.1 0.1

11 MAR <0.1 0.2 0 <0.1 < 0.1 0.1 <0.1 0.1

13 APR 0.1 0.2 0 0 <0.1 <0.1 0 <0.1

15 JUN 0.2 0.6 <0.1 0.2 0.2 0.3 <0.1 0.3

17 JUL 0.5 1.2 0.1 0.2 0.5 0.2 <0.1 0.4

6-9

not surprising since they normally live in association with colonies of

soft bodied sessile invertebrates. Caprellids were collected in very

low densities from fall through spring and none were taken at either sta-

tion in April. Together, gammarid and caprellid amphipods usually ac-

counted for less than 5% of the total catch (Table 6-1).

Cumaceans (Fig. 6-le) represent a third major group of pericarid

crustaceans. These little known animals tend to spend much of the time

buried in the sediment. Benthic sampling devices such as corers and

grabs have been used to collect cumaceans from estuarine and deep ocean

bottoms. The epibenthic sled is designed not to disturb the sand and

mud creek bottoms, yet some cumaceans were collected on every major

cruise. Densities were usually less than 1/m3 and no regular pattern of

abundance was observed between stations or cruises (Table 6-2). With the

exception of the December NMF collections, cumaceans were minor constit-

uents of the total catch (Table 6-1).

Leucon americanus, the most commonly collected cumacean, occurred at

both stations on all cruises. CycZaspis varians, Oxyurostylis smithi,

and at least two unidentified species were also collected at NMF and SJ.

Useful taxonomic references for the cumaceans of this area are Watling

(1979) and Zimmer (1980).

Isopods (Fig. 6-1d) constituted the fourth major group of pericarid

crustaceans collected in the sled study. These small (generally less

than 15 mm) dorsoventrally flattened crustaceans occur in estuarine

waters throughout the year. Some species remain buried in the sediment,

while others are associated with sponges and macrodetritus. Many are

6-10

parasites of fishes. More than 70 species are known from South Carolina

waters (Kelley, 1978).

The weak swimming species Edotea montosa was the most commonly col-

lected isopod at NMF and SJ. Aegathoa ocuZata, a strong swimmer, was al-

so collected on most cruises. Cassidinidea lunifrons, at least one spe-

cies of Chiridotea, and several unidentified species were taken less fre-

quently. Menzies and Frankenberg (1966) provide descriptions of most

local isopods.

Isopods were always most abundant at SJ; however, the densities at

both creeks were generally less than 1/m3 (Table 6-2). Some isopods

were collected on every major cruise except April at NMF, but they were

most abundant in summer collections.

B. DECAPOD CRUSTACEANS

Most familiar crustaceans including the commercial shrimps, crabs,

and lobsters belong to the Order Decapoda. More than 270 species of

decapods occur in the marine waters of South Carolina (Young, 1978), and

approximately 50 species of shrimps and crabs have been collected at

NMF and SJ (Allen, unpublished). At least 12 species of decapod shrimps

were collected with the epibenthic sled.

Two species of sergestid shrimps, Lucifer faxoni (Fig. 6-3b), and

Acetes cmericanus (Fig. 6-3c), were collected in sled and zooplankton

tows only during the warmest months (Table 6-3). These small shrimps

are regarded as members of the coastal plankton, but they are regularly

collected in high salinity regions of North Inlet and Winyah Bay. Al-

6-11

c~~~~~~~~~~~~

Figure 6-3. Decapod Crustaceans: a. postlarva of penaeid shrimp (7 mm);
b. Lucifer f'axoni, adult sergestid shrimp (10 mm); c. Acetes
coneri-canun, adult sergestid shrimp (10 mm)I

6-125

Table 6-3. Mean densities of juvenile (including postlarval) shrimps,
Lucifer faxoni and Acetes americanus, expressed as number of
organisms per cubic meter of water filtered.

JUVENILE SHRIMP Lucifer faxoni Acetes americanus
CRUISE MONTH NF SJ NF SJ NF SJ

1 AUG 0.3 0.2 3.6 4.4 1.0 5.1

3 SEP 0.1 <0.1 <0.1 0.1 <0.1 0.4

5 NOV 0.3 0.7 0.1 0.1 0 0

7 DEC 0.1 0.2 0 0 0 0

9 JAN 0.3 0.6 0 0 0 0

11 MAR 0.3 0.7 0 0 O 0

13 APR 0.4 0.1 0 0 0 0

15 JUN 0.4 11.2 0.2 0.1 0.1 0.3

17 JUL 0.5 0.7 0.1 <0.1 0.1 0.2

6-13

though Lucifer and Acetes are more effective swimmers than most zoo-

plankton, their occurrence in estuaries probably is related more to

their passive transport with penetrating coastal water masses than to

active migration. Densities of both shrimps were generally higher at

SJ than at NMF (Table 6-3).

Acetes was generally more abundant than Lucifer in the sled sam-

ples (Table 6-3). Williams (1965) provides some information on the

distribution of Acetes in North Carolina estuaries; however, little is

known about the life history and ecology of this shrimp. 'Maximum size

for Acetes is about 26 mm (Williams, 1965).

Early workers (e.g., Brooks, 1882) believed that Lucifer was a pri-

marily estuarine species, but recent studies suggest that it is widely

distributed in the Atlantic and Pacific Oceans to a depth of 100 m (Wil-

liams, 1965). Bowman and McCain (1967) studied the distribution of this

shrimp in the western North Atlantic.

Small shrimps (25 mm) of the genera Periclimenes, Latreutes, and

Neopontonides were frequently collected in sled samples which contained

excessive amounts of sponges and soft corals. These decapods live near

the bottom in shallow marsh waterways and are usually associated with

sessile benthic communities. Lysmata and Ogyrides were also collected

in sled tows at NMF and SJ Creeks. None of these small decapod shrimps

was collected with enough regularity or in sufficient numbers to deter-

mine its spatial or temporal distribution. In general, little is known

about the life cycles and ecology of these small shrimps.

PaZaemonetes pugio is by far the most common small decapod shrimp

6-14

in temperate marsh waterways. Two other species of PFqcemonetes, also oc-

cur in the study area (Young, 1978), but are much less abundant. Micro-

scopic examination is necessary to distinguish the three species. Grass

shrimp are typically found along marsh creek banks and in pools on the

marsh surface. They are excellent swimmers, but spend much of their

adult lives walking and feeding on detritus laden bottoms and obstructions.

Few adults are collected in sandy areas or swimming in the water column.

It is unlikely that any other decapod shrimp is as abundant in the study

area as Palaemonetes. Densities of thousands per cubic meter have been

recorded in North Inlet creeks (Allen, unpublished).

Female decapod shrimps carry eggs on abdominal pleopods and eventu-

ally release small (<1 mm) larvae which remain in the water column as

zooplankters until they grow to several millimeters in length and develop

a stronger affinity for the bottom. The identification of decapod shrimp

larvae is very difficult and no attempt to determine the taxonomic com-

position of the sled catch was made. Fig. 6-4 shows the distribution of

all shrimp larvae retained by the 365pm mesh sled net. A distinct sea-

sonal trend was apparent and consistent with other observations on the

occurrence of gravid female shrimp. Densities at both creeks were great-

est during the warm months and lowest from October to April. The de-

crease in abundance of shrimp larvae in July and August may indicate that

peak spawning may occur in early summer and again in early fall, but only

preliminary evidence for a bimodal pattern is available at this time.

Larvae were somewhat more abundant at NMF (Fig. 6-4),

In the analysis of the sled collections, all decapod shrimps which

had developed beyond the planktonic larval stages were regarded as juve-

6-15

; ~ ~ ~ ~ ~~~~~~~J Sl lll! Ili'l � 1" .
I!~~~~

I~~~~

9 SHRIMP LARVAE 3

I
a a1 I

E
" 1~~~~~~~~~~a

Z 3 i( . ~ d
a
aI

*~ ~~, !t ',,
o . _ I

Cruise 1 3 5 7 9 1 1 13 15 17
Month A S S O N N D J J F M M A M J J J A
N~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

O -
0-

Cruise 3 5 7 9 11 13 15 17

Month AS S O N N D J J F M M A M J J J A

Figure 6-4. Mean densities (no./m3) of shrimp larvae in epibenthic sled
collections on cruises 1 - 18 at NMF (above) and SJ (below).
Vertical lines indicate plus or minus the standard error.

6-16
' ,I'-.L' '
% ai

Cruise I 3 5 7 9 II 13 15 173
Month A S SO0N N D J J F M M A M J J A

Figure 6-4. Meart densities (no./m3) of shrimp larvae in epibenthic sled
collections on cruises 1 - 18 at NMF (above) and SJ (below).
Vertical lines indicate plus or minus the standard error.

6-16

niles. These forms were usually greater than 4 mm in length and often

had developed enough of the adult characteristics so that they could be

identified as palaemonid, penaeid, or other shrimps. The abundance of

juvenile shrimps was usually less than 1/m , but high densities of post-

larval and juvenile penaeids were collected at SJ in June (Table 6-3).

Although some penaeids were collected in July, most juvenile shrimp in

sled collections were palaemonids. Some juvenile shrimp were collected

each month.

The abundance of all shrimps (larvae, juvenile, and adults) collect-

ed with the epibenthic sled is shown in Fig. 6-5. The seasonal pattern,

with maximum densities in summer and minimum densities in winter, was

similar to that observed for the larvae, but total shrimp densities were

significantly higher than larvae densities from December to June (Fig.

6-4 and 6-5), especially at SJ. This difference was due to the occur-

rence of adult grass shrimp (Pa/aemonetes) on the creek bottoms. During

the cold months, grass shrimp move from the edges of the creeks to the

deeper channels. Aggregations on the channel bottoms were frequently so

large when water temperatures were below 109C that tens of thousands of

10-20 mm adults were taken in otter trawl collections. Grass shrimp

adults were much more abundant at SJ. Even though adult grass shrimp

were collected in practically every sled tow during the winter, none oc-

curred from spring to fall.

The largest shrimps which occur in South Carolina estuaries are the

penaeids. White shrimps (Peneaus setiferus), brown shrimps (P. aztecus),

pink shrimps (P. duorarwm), and spotted shrimps (Trachypeneaus constric-

tus) were collected at both creeks. The results of the trawl study on

6-.17

I8- TOTAL SHRIMPS

Z 12 I

. . .I. . . . . . . . . . . . . . .

Z 6 'j
0, I \

Cruise I 3 5 7 9 II 13 15 17
Month A S S O N N D J J F M M A M J J J A

181

12
o) I'

0I
z 6 ,

Cruise 3 5 7 9 . II 1 15 17. . . . . . .
Month A S S O N N D J J F M M A M J J J A

Figure 6-5. Mean densities (no./m3) of total shrimps in epibenthic sled
collections on cruises 1 - 18 at NMF (above) and SJ (below).
Vertical lines indicate plus or minus the standard error.

6-18

the distribution and abundance of the commercial shrimps at NMF and SJ

are discussed in Chapter 7, so only comments pertinent to the occurrence

of early life stages in sled collections are presented here.

Adult penaeid shrimps release demersal eggs in the ocean and several

planktonic stages are passed before postlarval shrimps (Fig. 6-3a) migrate

into estuarine nursery grounds (Linder and Anderson, 1956). After a peri-

od of rapid growth, penaeid shrimps return to the ocean. Postlarval and

small juvenile penaeid shrimps were taken in sled collections at NMF and

SJ. Additional information on the occurrence of young penaelds in the

study area is given in Chapter 7.

Other decapod shrimps represented in sled samples included various

life stages of cryptic burrowing species such as UpogebI'a, Callianassa,

and Aipheus. Adults of these common decapod crustaceans were not collect-

ed with the sled; however, late larval stages were common in sled samples

from both creeks during the summer.

At least 187 species of anomuran and brachyuran crabs are known from

coastal South Carolina (Young, 1978), and, although many are habitat

specific and live in ocean waters far from shore, the majority live in

shallow areas. Relatively few are truly estuarine organisms, but the

abundance and ecological significance of a few inshore species is immense.

The most familiar of the anomurans are hermit crabs. Adult hermit

crabs of the genera CZibanarius and Pagurus walk on the creek bottoms.

Only small hermit crabs which had recently settled from their planktonic

larval stages were captured with regularity. Densities of shell-less
I ~~~~~~~~~~~~~~~~~~3
hermit crabs were never greater than 1/m , and they occurred at both

6-19

creeks during the summer cruises.

The familiar walking and swimming crabs are brachyurans. Few adult

brachyurans were collected with the sled, but juvenile Libinia, Cancer,

Eurypanopeus, Menippe, Panopeus, Pilumnus, Pinnixa and Pinnotheres were

taken. Swimming crabs of the genera Portunus, Callinectes, and OvaZipes

were generally more common than other types.

The life cycle of decapod crabs includes several planktonic larval

stages. The common blue crab, Callinectes sapidus, has a life history

pattern which is only slightly different from other estuarine brachyurans.

Female crabs mate in brackish water from February to November and produce

an egg mass which contains up to two million eggs. Eggs hatch in about

two weeks and the zoea larvae which emerge are only a fraction of a mil-

limeter in size. Zoeae molt six or more times during the next several

weeks, but they remain planktonic forms until they molt into megalops

larvae (Fig. 6-6a). A first crab stage emerges from the megalops' and

at this stage, the animal finally resembles the adult.

Since many zoeal stages of brachyurans are too small to be retained

by the mesh of the sled net, zoeae were not enumerated in the sled sam-

ple analyses. Densities of crab zoeae in zooplankton collections at NMF

and SJ were reported in Chapter 5. Megalopae were retained by both the

zooplankton and sled meshes and the densities of these larvae determined

with the two gear types are presented in Figures 6-7 and 6-8. The same

general pattern of seasonal abundance was observed for both gear types

at both creeks. Megalopae densities decreased from fall to nearly zero

during the cold months, then increased sharply in May and June. Denst-

6-20.

a. b.

1 .4~~~~~~~~~~~~

I C. _ _ _ _ _~C

I ~~~Figure 6-6. a. crab megalops (4 mm); b. stomatopod larva (10 mm);

i5 ~~~~~~c. sciaenid fish larva (5 mm); d. anchovy larva (6 mm)

6-21

CRAB MEGALOPAE

30 '
z 30

O .-_-r-_... _____.._.________.___ _____

Cruise I 3 5 7 9 II 13 15 17
Month A S S 0 N N D J J F M M A M J J J A

90 '

60 ' ,

30S

I I I

O --------- ;-*- - ---
0 � ." """ .-..... ...........5 V/

Cruise I 3 5 7 9 1 1 13 15 17
Month A S S 0 N N D J J F M M A M J J J A

Figure 6-7. Mean densities (no./m3) of crab megalopae in zooplankton
collections on cruises 1 - 18 at NMF (above) and SJ (below).
Vertical lines indicate plus or minus the standard error.

6-22

84 CRAB MEGALOPAE

I 56

E
z 28

Cruise I 3 5 7 9 i I 13 15 17
Month A S S O N N D J J F M M A M J J J A

56-

z 28 f ,

k. . . . . . . . . . . . . . . . .
Cruise 1 3 5 7 9 1I 13 15 17
Month A S S O N N D J J F M M A M J J J A

Figure 6-8. Mean densities (no./m3) of crab megalopae in epibenthic sled
collections on cruises 1 - 18 at NMF (above) and SJ (below).
Vertical lines indicate plus or minus the standard error.

6-23

ties decreased after the early summer peak, SJ densities were greater

than those at NMF. Sled and zooplankton net densities were comparable

at NMF on all cruises, but they differed significantly at $0 in August

when the zooplankton mean was about ten times larger than the sled

mean. Large standard errors of the means indicate the magnitude of

the variability between bihourly collections made over a 24 hour period.

Many species of crabs were represented in the megalopae collections,

but fiddler crabs (Uca spp.) probably accounted for the largest propor-

tion. Crab reproduction is often synchronized with lunar cycles (see

references in Chapter 5), and with the frequency of sampling in this

study, only a limited amount of information on megalopae abundance was

obtained. Megalopae densities were low in September and November (Fig.

6-7 and 6-8), but they accounted for a large proportion of the catch

(Table 6-1). Megalopae were the dominant organisms at SJ and second

most abundant at NMF in June (Table 6-1).

C. STOMATOPODS

Stomatopods or mantis shrimps are morphologically, thus taxonomically,

distinct from the decapod crustaceans. Squilla empusa is the only spe-

cies regularly encountered in temperate estuaries. This lobsterlike

animal lives in burrows in marsh creeks and tends to be more common in

net catches after dark. Adults are usually from 60-150 mm in length.

Sometimes large numbers of S. empusa are caught in commercial shrimp

trawls in the ocean. Mantis shrimp or "thumbsplitters" (named for the

damage inflicted by a sharp edge of the second leg) have large abdomens

which are of commercial value in some areas.

6-24

Female stomatopods carry their eggs until they hatch. Developmen-

tal stages of S. empusa occur in the plankton throughout the warm season.

Late larval stages (Fig. 6-6b) were collected in the epibenthic sled on
3
most spring and summer cruises, but densities were always less than 1/m3.

No difference in the abundance of stomatopod larvae was seen between the

two creeks.

D. CHAETOGNATHS

Chaetognaths or arrowworms were often the dominant organisms in sled

collections at NMF and SJ (Table 6-1). These 'holo' forms were distributed

throughout the water column, especially during the warm months. Densi-

ties of chaetognaths in sled and zooplankton collections are discussed

in Chapter 5.

E. CTENOPHORES

Ctenophores or comb jellies are soft bodied, oval-shaped organisms.

Adults are typically less than 100 mm in length and can be distinguished

from true jellyfishes by the presence of rows of synchronously beating

hairs or cilia. Ctenophores occur in most temperate high salinity estu-

arine and ocean areas. Calder and Burrell (1978) listed five species

which occur in South Carolina waters. Mnemiopsis leidyi was frequently

observed in NMF and SJ Creeks. This widely distributed ctenophore has

been studied in the Chesapeake estuary by Bishop (1972), Miller (1974),

and Burrell (1976). Mnemiopsis is a major predator of zooplankton, and

high densities of ctenophores may strongly influence zooplankton abundance

and distribution. Beroe ovata, a larger, less common comb Jelly, consumes

6-25

smaller ctenophores such as Bolinopsis vitrea (Swanberg, 1974} and M,

leidyi (Sandifer et al. 1980).

Ctenophore densities are difficult to measure because the fragile

animals break into amorphous fragments when they are caught in nets.

Those which remain intact disintegrate when formalin preservative is

added to the collection. No density information was recorded in the

present study, but numbers were sometimes so large that several liters

of jelly were caught in a tow. Large variations in numbers between con-

secutive tows indicated a patchy distribution in the water column.

F. CNIDARIANS

The true jellyfishes of the Phylum Cnidaria are usually more abundant

than ctenephores in South Carolina estuaries. The taxonomy of the local

cnidarians is summarized by Calder and Hester (1978). Large species

such as StomoZophus meleagris (jellyball) and Chrysaora quinquecirrha

(sea nettle) were frequently observed in Winyah Bay, SJ and NMF during

the warm season. Large jellyfishes or medusae are relatively good swim-

mers and tend to occur in groups. Dozens of other medusae are less con-

spicuous because of their size and lack of pigmentation. Medusae were

not enumerated in the sled samples, but BougainvZlZia sp. and other small

forms were occasionally very abundant. There was no evidence of vertical

stratification by medusae in the marsh creeks.

G. MOLLUSCS

The Phylum Mollusca includes the common estuarine clams, snails, and

squids. Most are benthic organisms which live on or in the sediment as

6-26

adults. Since the epibenthic sled does not dig into the substrate, no

adult molluscs were collected, but small (.1-5 rmm) clams and snails which

had recently settled from planktonic larval stages (veligers) were swept

into the sled net on most tows. Recently settled clams were not enumer-

ated in the sample analyses; but they were most abundant from spring to

fall. These molluscs were frequently identified in the guts of small

bottom feeding fishes such as the spot and Atlantic croaker.

H. ANNELIDS

Polychaete worms are benthic organisms which, like molluscs, produce

planktonic larval stages. Very few adult worms were collected with the

sled, but late larval stages and small adults were not uncommon. It is

not known whether some polychaetes swim just above the bottom or whether

unburied worms become suspended and collected by the sled.

Leeches, which are also members of the Phylum Annelida, occurred in

the majority of sled collections from November through March. Calliob-

della vivida was frequently collected at both creeks. Free swimming

adults (.5-15 mm) were conspicuous in the samples and the same parasites

were often observed attached to herring and menhaden fish hosts collected
3
in the trawls. Densities were usually less than 1/m3

I. FISHES

More than 100 species of fishes inhabit South Carolina estuaries

(Poole, 1978) and the early life stages of many of these species inhabit

marsh creeks like NMF and SJ. Fish eggs are difficult to identify and

6-27

no attempt was made to distinguish species represented by eggs tn the

zooplankton and sled net collections, Most of those collected were

planktonic (semibuoyant or free floating) types, but some demersal (ad-

herant to bottom materials) eggs were also taken. Few eggs were collect-

ed during the cold months.

Fish larvae are generally less than 2 mm in length when they emerge

from eggs. These fragile forms continue to absorb yolk material for days

before they begin to feed. At this stage the larvae do not have the full

adult complement of fin spines and rays and rarely resemble adults of

the species in shape or color. Identification is usually very difficult

until they reach several millimeters in length. The earliest develop-

mental stages are weak swimmers and are distributed throughout the water

column. The majority of estuarine species of fishes have strong affini-

ties for the bottom as adults, and after they become strong enough swim-

mers, the larvae of these species occur closer to the substrate. The

epibenthic sled is a relatively effective device for capturing fish lar-

vae in the marsh creeks, but some caution must be taken in interpreting

sled determined densities since avoidance of the collection apparatus by

larvae probably results in only a fraction of the larvae being collected.

Fish larvae were identified to the lowest taxon possible and mea-

sured, and data on the seasonal occurrence and length frequency of larval

fishes are discussed in Chapter 7.

In general, fish larvae (Fig. 6-9) followed a trend similar to that

observed for shrimp larvae and megalopae. Low densities were typical

during the cold months, and an abrupt increase in May and June marked an

6-28

I18-. FISH LARVAE

,
2

Cruise 1 3 5 7 9 1 1 13 15 17
Month A S S O N N D J J F M M A M J J J A

n 12

I`~~~~-,~~~ \

Cruise I 3 5 7 9 1 1 13 15 17
Month A S S 0 N N D J J F M M A M J J J A

Figure 6-9. Mean densities (no./m3) of fish larvae in epibenthic sled
collections on cruises 1 - 18 at NMF (above) and SJ (below).
Vertical lines indicate plus or minus the standard error.

6-29

early summer peak, Collections in early summer were dominated by an-

chovy (Fig. 6-6d), goby, and blenny larvae, but a great diversity of spe-

cies was represented. The SJ peak was earlier and higher than the NMF

peak, which persisted until later in the summer. The diversity and

relative abundance of species was similar at both creeks,

The small February peaks at both creeks (Fig. 6-9) indicate an in-

flux of young of the year spot larvae (Fig. 6-6c). Ocean-spawned spot

migrate into estuaries in January and February each year (e.g., Wein-

stein, 1979), and numbers of these larvae are collected in the sled until

spring, when they become too large and evasive to be captured with this

device.

J. TOTAL ORGANISMS

The abundance of all organisms collected in the epibenthic sled sam-

ples is shown in Fig. 6-10. Maximum densities occurred in August, June,

and July at both creeks and the presence of larval crustaceans, fishes,

and chaetognaths account for these peaks (Table 6-1). Winter densities

were generally less than twenty organisms per cubic meter; however,

January peaks were prominent features of the seasonal curves for both

creeks. These peaks represent the seasonal maxima for mysid shrimp

(Neomysis americana) populations. Mysids were by far the most abundant

organisms at both creeks on the December, January, March, and April

cruises (Table 6-1). Without exception, total organisms densities were

greater at SJ than at NMF (Fig. 6-10).

It is difficult to compare the actual densities of sled collected

6-30

144- TOTAL ORGANISMS

: 96

Cruise 1 3 5 7 9 1 1 13 15 17
Month A S S O N N D J J F M M A M J J J A

144 .

E
48- \ I

. . . . . . . . . . . . . . .

Cruise I 3 5 7 9 1 1 13 15 17
Month A S S 0 N N D J J F M M A M J J J A

Figure 6-10. Mean densities (no./m3) of total organisms in epibenthic sled
collections on cruises 1 - 18 at NMF (above) and SJ (below).
Vertical lines indicate plus or minus the standard error.

6-31

organisms at NMF and SJ to the abundance and distribution of similar or-

ganisms in other estuaries because so little quantitative information is

available for other areas. This study appears to be the first comprehen-

sive attempt to characterize the abundance of motile epibenthic popula-

tions in a South Carolina estuary, and the authors are not aware of any

comparable studies from other east coast systems. Sled collections will

be made at NMF, SJ, and some locations in WRinyah Bay for the next several

years to provide insight into the spatial and temporal variation in abun-

dance and community structure.

Epibenthic organisms constitute important links in estuarine food

webs by assimilating marsh productivity (-plant detritus and microalgae)

and making that energy available to higher trophic levels. It is impor-

tant that more information about the ecology and physiology of these or-

ganisms is gathered so that their vulnerabilities to environmental per-

turbations can be assessed. What is already clear is that damage to peri-

carid crustacean and larval populations by pollutants would have far

reaching implications for the survival of productive estuaries.

6-32

CHAPTER 7. SHRIMPS, CRABS, AND FISHES

The distribution, abundance, and survival of early life stages of

3 ~~~shrimps, crabs, and fishes ultimately determine the success of the commer-

cial and recreational fisheries. The occurrence of crustacean and fish

I ~~~larvae at NMF and S~J was discussed in Chapters 5 and 6. This information

3 ~~~provides a background for the interpretation of the adult macroinvertebrate

and fish collection data presented here. In this chapter, results of trawl

3 ~~~and gill net collections made on major cruises at NMF and 53 are combined

with general information on the ecology of three species of penaeid shrimps,

I ~~~the blue crab, a stomatopod, a squid, and efghty-five species of fishes.

I. SHRIMPS

The shrimp fishery ranks first in terms of value of all fisheries in

3 ~~~South Carolina and in'the United States (U.S. Dept. of Commerce, 1971-1980).

The fishery is based on three species of penaeid shrimps which inhabit the

5 ~~~southeast and Gulf coasts. Most of the commercial effort is concentrated

in open coastal waters within a few kilometers of the shore, but shallow

I ~~~marsh estuaries are essential to the completion of the life cycle of pen-

aeid shrimps. The life history strategies of the white, brown and pink

shrimps are similar. Planktonic larvae develop from eggs spawned by adult

3 ~~~shrimps in the ocean, and postlarval shrimps migrate into estuaries where

5 ~~~~~~~~~~~~7-1

they grow to adult size at a rapid rate. Adults are harvested in the es-

tuaries and coastal waters during the warm months.

A. WHITE SHRIMP (Penaeus setiferus)

White shrimps occur in coastal waters from North Carolina to Mexico,

but they are most abundant in the Gulf of Mexico adjacent to the Miss-

issippi Delta. In South Carolina, white shrimps are usually the most

important species in the fishery (U.S. Dept. of Commerce, 1971-1980).

Adult white shrimps spawn from May to September in ocean areas close

to shore (Linder and Anderson, 1956). Large reproductively active

white shrimps, referred to as "roe" shrimps, comprise a valuable spring

fishery off South Carolina beaches.

The developmental sequence from egg-nauplius-protozoea-mysis-post-

larva usually takes about two weeks. By the time the postlarval shrimps

are about 7 mm in length, they have developed a stronger affinity for

the bottom than the smaller planktonic stages (Williams, 1965). Post-

larvae migrate from coastal waters into estuarine areas and grow at

the rate of more than I mm per day. Postlarvae and small juvenile

white shrimps tend to seek low salinity habitats within the estuary,

but as the young shrimps mature, they move to saltier and deeper areas

where they remain until they migrate back to the ocean as adults (Wil-

liams, 1955).

In late fall, juvenile and small adult white shrimps move to deep

areas in the lower estuary where they overwinter. White shrimps are

the most active of the penaeids and are known to migrate for consider-

7-2

able distances southward along the coast in the fall (Linder and Ander-
son, 1956). It is not known to what extent the spring coastal return

migrations contributes to the local population, but white roe shrimp

populations are probably composed of both overwintering residents and
spring migrants.

White shrimps have a preference for soft mud over sandy or shelly

substrates (Williams, 1958). Postlarvae, juveniles and adults eat al-

gae, vascular plant detritus, and small invertebrates of many kinds,
although they occasionally capture small fishes and squids (Williams,
1965).

White shrimps were by far the most abundant penaeids collected in
NMF and SJ creeks during the summer and fall (Fig. 7-1). In August,
similar numbers were collected in trawls at the two creeks (Fig. 7-1),
but the NMF shrimps were smaller (Fig. 7-2) and weighed less (Fig. 7-3)

than the SJ shrimps. Total numbers were greater in September, espe-
cially at SJ Creek (Fig. 7-1). The length frequency analysis for white

shrimps in the September collections indicated that fewer small shrimps
were present (Fig. 7-2). Mean length and weight of white shrimps was

somewhat greater at NMF in the September collections (Fig. 7-2 and 7-3).
White shrimp abundance and the length frequency structure remained un-
changed on the November cruise (Fig. 7-1 and Fig. 7-2).

A large reduction in the abundance of white shrimps occurred before
the December cruise and almost none were collected for the remainder of

the trawl study (Fig. 7-1). Those collected from December to March
were small individuals (Fig. 7-2),

7-3

* White Shrimp
1500 -
Brown Shrimp

D Pink Shrimp

'
a. 1000 -

500

M ma No -
b.
.-

JQ_ I
E
z
500 '

Month Aug Sep Nov Dec Jan Mar Apr Jun Jul

Figure 7-1. Total numbers of adult penaeid shrimps in trawl collections on major cruises. First column
of each couplet indicates numbers for NMF, second column for SJ.

m m _ mm _ _ _m _ - _m

m - ininininin~~~~~~~~~~~~~~~~~2o

200
120 Aug - Nov

1 20 -
40

E
40
--

Sep

200 40 Dc
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
0 _
EI
Z

120 401 Jan

40- 40f Ma r

I I I I I I~~~~~~~~~~~~~~~~~~~~~~~~~~~ I I
10 20 30 40 5o 60 70 10 20 30 40 50 o60 70

Carapace Length In Millimeters

Figure 7-2. Length frequency analysis of white shrimps (P. setiferus) in trawl collections on
major cruises at NMF and SJ. Height of each bar indicates total number of white
shrimps of that size class at both creeks. Shaded portion of each bar represents
number collected at NMF.

* White Shrimp

6000 -Pt:
~~~~~~~6000 -~ ~ ~ ~ ~ ~i [ Brown Shrimp

E Pink Shrimp

......

' 4000 , .
E
a~~~~~~~ "' ...

2000-

2--:.

Month Aug Sep Nov Dec Jan Mar Apr Jun Jul

Figure 7-3. Total weight of adult penaeid shrimps in trawl collections on major cruises. First
column of each couplet indicates numbers for NMF, second column for SJ.

e- m_ _ m M a - a a a a a a a a a_

The seasonal pattern of abundance reported here is consistent with

the general pattern for white shrimp distribution, Juvenile and young

white shrimp populations were established in the creeks before the

first samples were collected in August. Increasing numbers of adults

moved into the high salinity creeks, presumably from lower salinity

regions of Winyah Bay. Decreasing temperatures in November probably

triggered a migration of adult white shrimps to the ocean, but some

young shrimps remained in the creeks through the winter.

White shrimps were consistently more abundant at SJ Creek, The to-

tal number of white shrimps collected on each cruise increased from

August to November at South Jones Creek, but decreased at No Man's

Friend (Fig. 7-1). Of the more than 5100 white shrimps analyzed in

the study, more than 3700 (73%) were collected at SJ Creek.

B. BROWN SHRIMP (Penaeus aztecus)

Brown shrimps occur from North Carolina to South America. Adults

spawn in deep coastal waters during the winter, and, although postlar-

vae have been collected in North Carolina estuaries from October to

May, peak recruitment is in early spring (Williams, 1959). Bearden

(1961) reported peak abundance for brown shrimp larvae in South Caro-

lina estuaries in February and March. Postlarvae, which arrive in

shallow marsh waterways during the coldest periods, probably die

(Williams, 1955). Growth rates for postlarval brown shrimps (1.5 mm/

day) may be somewhat greater than those measured for white shrimps

(Williams, 1955).

7-7

In South Carolina, brown shrimps do not inhabit low salinity estu-

arine areas which are sought by white shrimps later in the warm season.

Brown shrimps are burrowers and seem to be more abundant on sandy mud

substrates than on soft mud bottom.

The temporal segregation of the white and brown shrimps is distinct

in most areas. Brown shrimps occupy the estuarine nursery grounds in

early summer and adults leave the area by early fall, As adult brown

shrimp abundance in the creeks decreases, young white shrimps arrive.

This pattern was observed at both NMF and SJ Creeks (Fig. 7-1).

On the August cruise, adult brown shrimps were about twice as abun-

dant at SJ Creek, but the numbers collected at both creeks were less

than those for white shrimps (Fig. 7-1). The mean size and weight of

brown shrimps in August was greater than those for white shrimps (Fig.

7-2, 7-3, 7-4). In September, few brown shrimps were collected. Very

few small individuals remained in the creeks during the cold months.

Postlarval brown shrimps were collected with the epibenthic sled in

March. Juveniles occurred in trawl collections on the spring cruises

and adults were collected in June and July. The large increase in the

number of adult brown shrimps from June to July is probably related to

the movement of individuals into the creeks from adjacent shallow

flats where juveniles appeared to be more abundant. The mean carapace

length of all brown shrimps caught in June was about 33t5 mm and the

mean length in July was about 4216 mm.

C. PINK SHRIMP (Penaeus duorarum)

The pink shrimp has a discontinuous geographical distribution between

7-8

20 Mar
Aug
140 -

Jun
100-Ju

Jul
6S0 -

E
CL

20 �140

0w 20 ~~Sep 100

z. 2
20

~2011~~L ~ Nov 60

Dec
201 20-

20 30 40 50 60 70 20 30 40 50 60 70

Carapace Length In Millimeters

Figure 7-4. Length frequency analysis of brown shrimps (P. azteous) in trawl collections
on major cruises at NMF and SJ. Height of each bar indicates total numbers
of brown shrimps of that size class at both creeks. Shaded portion of each
bar represents number collected at NMF.

North Carolina and South America. Endemic populations large enough to

support commercial fisheries occur in North Carolina, Key West, and

Campeche (Mexico). South Carolina densities are comparatively small

and the pink shrimp accounts for less than 5% of the total landings

(Sandifer et al., 1980).

The spawning season of the pink shrimp is similar to that of the

white shrimp, May through September (Williams, 1965). Postlarvae

enter South Carolina estuaries from May through September (Bearden,

1961b) and move from shallow, less saline areas to deeper creeks and

channels closer to the ocean as they mature (Williams, 1965).

Pink shrimps inhabit coarser substrates than white shrimps and often

remain completely buried (Williams, 1958). This relatively inactive

penaeid overwinters in high salinity estuarine areas. In North Caro-

lina overwintering populations are sometimes killed by extreme coid,

but in the spring, adults migrate to ocean spawning grounds (Williams,

1965).

Pink and white shrimps inhabit the estuaries at the same time, but

apparently reduce competition for space and resources by favoring dif-

ferent habitats. Pink shrimp catches at NMF and SJ were small (Fig.

7-1), yet some individuals occurred on all but the August and December

cruises. Pink shrimps were about five times more abundant at SJ.

The one-half inch mesh of the trawl net did not retain a high percen-

tage of the juvenile or small adult penaeid shrimps which passed into the

mouth of the trawl. Adult shrimps have very strong avoidance capabilities

7-10

and length frequency of blue crabs taken on all cruises is shown in Fig.

7-5. The majority of trawl caught crabs were juveniles less than 60 mm

in width. Young crabs less than 20 mm in width dominated the collections

in November and January. These small crabs represented summer and early

fall spawned young of the year. Large numbers of young were collected

throughout the cold months, but most had grown to more than 20 mm in

width by March. The low numbers of juveniles collected in March and the

absence of small crabs in April indicated the lack of recruitment to the

population during the winter. This observation is consistent with the

analysis of the zooplankton and sled collections.

Adult crabs avoided the trawl and few were collected on any cruise.

All but a few adult blue crabs captured in the trawl and gill net were

males. No general relationship between number or sex of adult blue crabs

and salinity was observed during the study. The dominance of male crabs

in these high salinity creeks is not consistent with the classic distribu-

tion of blue crabs described for other estuaries (e.g., Van Engel, 1958).

Crabs of all sizes were most abundant in the tidal creeks during the

cold months. From late spring through fall, crabs appear to be more ac-

tive and spend more time along shallow banks and on the marsh surface.

The concentration of relatively slow moving crabs in the creeks during

the cold months may account for larger catches from November through

April than from June through September.

With the exception of the August cruise, blue crabs of most sizes

were more abundant in NMF than SJ Creek (Fig. 7-5). About 1400 crabs

were analyzed from all collections and about 900 (65%) were frow NMF sam-

.7--3

60 Jan
Aug

20
20

Sep
20 - Mar
20

ae6
e~~~ 601~ ~Nov
to . llApr
0
60"

E~~~~~~~~ ~~~20 _|
602

Dec
Jun

20 1oL.~y Jul

20 40 60 80 100 120 140 160 180 20 40 60 80 100 120 140 160 180

Carapace Width In Millimeters

Figure 7-5. Length frequency analysis of blue crabs (C. sapidus) in trawl collections
on major cruises at NMF and SJ. Height of each bar indicates total number
of blue crabs of each size class at both creeks. Shaded portion of each
bar represents numbers collected at NMF.
m~~~ __ - -

pies. Juvenile crabs less than 30 mm width were especially abundant at

NMF.

The role of the blue crab in estuaries is extremely important. Crabs

are opportunistic organisms which procure food through scavenging and

predation; they may compete with shrimps and fishes for food and space.

The influence of blue crabs on other estuarine organisms is difficult to

measure, but field and laboratory observations of their aggressive life

style indicate that blue crabs must play a major regulatory role within

the ecosystem.

In addition to the blue crab, other brachyuran crabs were collected

in trawl samples at both creeks. These included other portunid crabs

(OvaZlipes ooellatus, Portunus gibbesii, P. spinimanus, and Callinectes

similis), majid crabs (Libinia emarginata and L. dubia), and xanthid

crabs (Panopeus herbstii and Eurypanopeus depressus). These species were

most abundant during the summer, but none was collected in sufficient

numbers to suggest it was a common inhabitant of the creek bottoms. How-

ever, small xanthids like Panopeus were not effectively sampled with the

trawl and other observations indicate that xanthid crabs are very abundant

on subtidal oyster and shell bottoms in certain parts of the creeks.

Adult hermit crabs were conspicuous by their absence in both creeks.

III. STOMATOPOD OR MANTIS SHRIMP (Squilla empusa)

Adult stomatopods were regularly collected in trawls from January

through November. Some 80-120 mm adults were caught from January through

June, but the greatest numbers occurred from August through November.

7-15

Stomatopods were usually more common in night tows than daylight collec-

tions. They appeared to be equally abundant at the two creeks. Stomato-

pods were probably much more abundant than trawl collections indicated.

The abundance and distribution of stomatopod larvae was discussed in Chap-

ter 6.

IV. SHORT-FINNED SQUID (nolliguncula brevis)

Squid are fast swimming shell-less molluscs which easily escape otter

trawls; however, the short-finned squid was caught in most trawl collec-

tions from April through November at both creeks. A total of 251 individ-

uals greater than 30 mm in mantle length were recorded during the study.

The largest collections were in April when similar numbers of 50-110 mm

(mantle length) squid occurred at both creeks. Adults with eggs were

taken in June and very small squid (<10mm) were found among bottom debris

in July trawls. Squid may migrate to deeper estuarine and coastal areas

during the coldest months.

Although squid constitute a significant portion of the shrimp fishery

by catch, they have little or no commercial value. Squid are used for

bait by local anglers. Gut contents of gars, bluefishes and flounders

caught in gill nets at both creeks frequently included squid.

V. FISHES

Although the finfish fisheries of South Carolina are not as large as

the shrimp and crab fisheries, many important commercial and sport fish

species occur in the estuaries and shallow ocean. More than 100 species

7-16

of fishes are known from the inshore waters of South Carolina (Poole,1978).

In this study, information on the fishes of NMF and SJ Creeks was

gathered from epibenthic sled, otter trawl, and gill net collections.

Between the three gear types, 85 species of fishes were identified, The

identification and length frequency analyses of larval stages collected

in the sled were instrumental in assessing the utilization of these creeks

by many of the 65 species caught with the trawl and 24 species caught in

the gill nets. This information is summarized in Table 7-1. General com-

ments on the life history, distribution, and relative abundance of each

species is presented in an annotated list of the fishes. The species are

discussed in the order in which they appear in Table 7-1.

A great deal of information on the ecology and life history of most

of the species which were collected in the creeks is available in the

scientific literature, but we have cited only those studies which deal

with broad aspects of their ecology. For further information on most of

these species, the reader is referred to Hildebrand and Schroeder (1928),

Bigelow and Schroeder (1953), Bohlke and Chaplin (1968), Dahlberg (1975),

and Hoese and Moore (1977).

The first part of this section is the annotated list of species.

This is followed by a discussion of fish community dynamics and a compar-

ison of the results of the NMF-SJ study with others conducted in Winyah

Bay and neighboring estuaries.

A. ANNOTATED LIST OF FISHES

Cartilaginous fishes such as sharks, rays and skates are relatively

Table 7-1. Taxonomic list of fishes collected with all gear types from August
1980 through July 1981. X indicates presence at No Man's Friend
(NMF) and South Jones (SJ) Creeks, in trawls, in gill nets (GN), in
epibenthic sled or zooplankton nets (SL/PLK). OCC. represents the
number of times the species occurred in trawl collections on major
cruises at either creek out of a total of 18 samplings (9 at NMF,
and 9 at SJ).

FAMILY GENUS-SPECIES COMMON NAME NMF SJ TRAWL GN SL/PLK OCC.

Carcharhinidae Carcharhinus obscurus dusky shark X X 1

Rhizoprionodon terraenovae Atlantic sharpnose shark X X X 4
Sphyrnidae Sphyrna lewinii scalloped hammerhead X X X 2

Dasyatidae Dasyatis americana southern stingray X X X 4

Dasyatis centroura roughtail stingray X X 1
Dasyatis sabina Atlantic stingray X X X X 4
Myliobatidae Rhinoptera bonasus cownose ray X X X 2

Lepisosteidae Lepisosteus osseus longnose gar X X X X 5
Elopidae Elops saurus ladyfish X X X X X 4

MegaZope atZantica tarpon X X 0
Anguillidae AnguiZla rostrata American eel X X X 4

Ophichthidae Bascanichthys sp. whip eel X X 1

Myrophis punctatus speckled worm eel X X X O

Ophichthus gomesi shrimp eel X X X ? 1

Clupeidae AZosa aestivalis blueback herring X X X ? 6
Brevoortia tyrannus Atlantic menhaden X X X X ? 14

Dorosoma cepedianum gizzard shad X X ? 2

Dorosoma petenense threadfin shad X X ? 1
Engraulidae Anchoa hepsetus striped anchovy X X X X 9
Anchoa mitchilli bay anchovy X X X X 17

Synodontidae Synodus foetens inshore lizardfish X X X X 7
Ariidae Arius feZis sea catfish X X X X 7
Bagre marinus gafftopsail catfish X X 1

Batrachoididae Opsanus tau oyster toadfish X X X 13
Gobiesocidae Gobiesox strurosus skilletfish X X X X 1

Gadidae Urophycis floridanus southern hake X X X 6
Urophycis regius spotted hake X X X 2
Ophidiidae Rissola marginata striped cusk-eel X X X 6
Cyprinodontidae Cyprinodon variegatus sheepshead minnow X X 1
hundulus heterocZitus mummichog X X X

Atherinidae Membras martinica rough silverside X X O
Menidia menidia Atlantic silverside X X X X 5

Syngnathidae Syngnathus fZoridae dusky pipefish X X X X 3

Syngnathus fuscus northern pipefish X X X 1
Syngnathus Zouisianae chain pipefish X X X X 3

Serranidae Centropristis phiZadelphica rock sea bass X X 1
Mycteroperca micro'epia gag grouper X X X 3

Pomatomidae Pomatomus saZtatrix bluefish X X X X 7

Rachycentridae Rachycentron oanaduw cobia X X 1

Carangidae Caranx hippos crevalle jack X X X X 5

ChZoroseombros chrysurus Atlantic bumper X X X 5
Setene vamer lookdown X X X 2

Lutjanidae Lutjanus griseus gray snapper X X X 1

Gerreidae Diapterus oiisthostomus Irish pompano X X X 2
Eucinostomus argenteus spotfin mojarra X X X ? 3
Eucinostomus guZa silver jenny X X ? 1

Pomadasyidae Orthopristis chrysoptera pigfish X X X X 2
Sparidae Archosargus probatocephaZus sheepshead X X X X 5
Lagodon rhomboides pinfish X X X X 11

7-18

Table 7-1 cont.

FAMILY GENUS-SPECIES COMMON NAME NMF SJ TRAWL GN SL/PLK OCC.

Sciaenidae BairdieZZa chrysura silver perch X X X X 14

Cynoscion nebuZosus spotted sea trout X X X X X 10

Cynoscion regalis weakfish X X X X X 1

Leiostomus xanthurus spot X X X X X 17

Menticirrhus americana southern kingfish X X X X 2

Menticirrhus Zittoralis gulf kingfish X X 1

Menticirrhus saratiZis northern kingfish X X X 2

Micropogonias unduZatus Atlantic croaker X X X X X 11

Pogonias cromis black drum X X 1

Scianops ocelZata red drum X X X X 3

SteZZlifer lanceolatus star drum X X X 0

Ephippidae Chaetodipterus faber Atlantic spadefish X X X 5

Mugilidae MugiZ cephaZus striped mullet X X X X 3

Mugil curema white mullet X X X 6

Blenniidae HypsobZennius hentzi feather blenny X X X X 3

Chasmodes bosquianius striped blenny X X 0

Gobiidae GobionelZus boZeosoma darter goby X X X 0

GobioneZlus nastatus sharptail goby X X X X 1

GobioneZZus shufeZdti freshwater goby X X X 0

Gobiosoma bosci naked goby X X X X 2

Gobiosoma ginsburgi seaboard goby X X X 0

Microgobius gulosus clown goby X X 0

Microgobius thalassinus green goby X X 0

Scombridae Scomberomorus macuZatus Spanish mackerel X X 1

Stromateidae Peprilus alepidotus harvestfish X X 1

PepriZus triacanthus butterfish X X 1

Triglidae Prionotus tribulus bighead searobin X X X X 4

Bothidae AncycZopsetta quadrocellata ocellated flounder X X X 5

Citharichthys spiZopterus bay whiff X X X X 7

Etropus crossotus fringed flounder X X X 12

ParaZichthys dentatus summer flounder X X X X X 4

Paralichthys Zethostigma southern flounder X X X X X 15

Soleidae Trinectes macuZatus hogchoker X X X X 8

Cynoglossidae Symphurus pZagiusa blackcheek tonguefish X X X X 17

Balistidae Monacanthus hispidus planehead filefish X X 0

Tetraodontidae Sphoeroides macuZatus northern puffer X X 0

7-19

large, slow swimming seasonal migrants to the study area, Three spe-

cies of sharks and three species of stingrays were caught in gill nets

at NMF and SJ Creeks. Bearden (1965) summarized information on the

elasmobranch fishes of South Carolina.

A 750 mm dusky shark (Carcharhinus obscurus) collected in July at

NMF constituted the only record for this common coastal shark. Fish

fragments were found in its gut. Young and small adult dusky and other

carcharhinid sharks are common in high salinity estuarine areas of

South Carolina.

Atlantic sharpnose sharks (Rhizoprionodon terraenovae) are the most

common small sharks in the salt marsh creeks and lower estuaries of

South Carolina. Adults release young in the spring and large numbers

of 350-600 mm individuals were collected in gill nets from June through

September. These voracious predators consumed shrimps, crabs, and a

variety of fishes. Young sharpnose sharks were equally abundant at

NMF and SJ. In the fall, sharpnose sharks apparently migrate to deeper

and warmer waters.

Scalloped hammerheads (Sphyrna lewinii) were common in gill net

catches in July and August. Individuals from 410-480 mm were more com-

mon at SJ than NMF. These young sharks probably originated from adult

spawning activity in the ocean during the spring. Gut contents in-

cluded penaeid shrimps and small fishes, especially menhaden.

Southern stingrays (Dasyatis americana) were collected in several

gill net sets in August and September; however, because of their large

7-20

size, these rays may have been more abundant than the gill net �atches.

indicated. Individuals ranged from 360-620 mm in width and usually con-

tained crushed clam shells (Macoma baZtica). Southern stingrays occur-

red at both creeks. One specimen (410mm) of the roughtail stingray

(Dasyatis centroura), a close relative of the southern stingray, was

collected in a gill net in August at NMF.

The most common ray was the Atlantic stingray (Dasyatis sabina).

Small rays with wing widths of 220-380 mm were frequently caught in

gill nets from April through November. On one occasion in August, a

370 mm female released three full term 130 mm young while being removed

from the net. Atlantic stingrays, also known as stingarees, may be

year-round residents of estuaries. They are collected in low salinity

portions of Winyah Bay as well as in the ocean. These rays occur on

mud and sand bottoms and consume a variety of shrimps, crabs, and rela-

tively slow moving benthic invertebrates.

Cownose rays (Rhinoptera bonasus) were caught in August at SJ Creek.

These fishes were 550-680 mm in width. Gut contents Included clam shell

fragments (Macoma baltica). Cownose rays are major predators of clam

populations and have been known to decimate large numbers of commercial-

ly valuable hard clams (Mercenaria mercenaria) in northern estuaries.

The longnose gar (Lepisosteus osseus) was caught in gill nets, and

occasionally in trawls, at both creeks. Gars are primarily freshwater

fishes, but are often found in brackish and high salinity estuarine

areas. The maximum size for this species is about 1500 mm; however,

the range for those caught in the study area was 650 to 930 mm. This

7-21

predator usually swims well above the bottom, and its pres~ence is often

revealed by its disturbance of the surface, Shrimps and fishes (espe-

cially menhaden) were usually in the guts of captured individuals.

Gars are probably year-round residents of the estuary, but none were

caught during the winter at either creek.

Ladyfish (Elops saurus) are sleek silvery gamefish which are common

in southeastern estuaries. Larvae were collected with the sled in De-

cember and June, and small juveniles were caught in cast nets and min-

now traps in marsh pools during most of the warm season. Gehringer

(1959) described the early development of ocean-spawned larvae. Adults

are fast swimming predators which avoid trawls, but 220-350 mm individ-

uals were occasionally snagged in gill nets from spring through fall.

A 22 mm tarpon (Megalops atlantica) larva (leptocephalus) was col-

lected with the sled in August at SJ. Large tarpon are summer visitors

to the ocean adjacent to Winyah Bay. It is not known whether any spawn-

ing occurs locally, yet larval and juvenile tarpon (to about 300 mm) are

commonly caught in upper marsh waterways during the summer,

The American eel (Anguilla rostrata) may be one of the most abundant

fishes in coastal marshes and estuaries, but because they are secretive

and are not well retained by trawl nets, the assessment of population

densities is difficult. These year-round residents are especially com-

mon around marsh banks and submerged obstructions. Postlarval elvers

or glass eels were collected in January, February and April with the

sled at SJ. Young eels migrate from spawning grounds in the deep Atlan-

tic Ocean near Bermuda, Eels are predators of many species of shrimps,

7-22

crabs and fishes. American eels have been found in the guts of red

drum, hammerhead sharks, and oyster toadfish in the study area, The

potential for a major commercial eel fishery in Winyah Bay appears to

be very good, but preliminary trapping surveys need to be conducted.

Three species of ophichthid eels were collected at South Jones

Creek. One shrimp eel (Ophichthus gomesi) and one whip eel (Bascanich-

thys sp.) were captured in September with the trawl. Little is known

about the ecology of either species, but they do not appear to be com-

mon in this region. Speckled worm eels (Myrophis punctatus), however,

are abundant in the marsh creeks of North Inlet all year. None of these

relatively small eels were taken in trawls, but adults are commonly ob-

served in'muddy intertidal substrates. Leptocephalus larvae (40-70 mm)

were collected in the majority of epibenthic sled tows from November

through March at both creeks.

The herrings comprise a well known family of estuarine and coastal

fishes. Two of the four species collected in the two creeks, blueback

herring (Alosa aestivalis) and Atlantic menhaden (Brevoortia tyrannus)

are of commercial importance. A close relative of the blueback is the

American shad (Alosa sapidissima), and, although this anadromous spe-

cies was not collected in this study, it is common in Winyah Bay. A

spring shad fishery intercepts adults moving from the ocean to river

spawning grounds. Blueback herring follow the same pattern. The young

of both species move from freshwater hatching areas to brackish and

high salinity areas where they remain for about one year. Young of the

year bluebacks (<120 mm) were taken in trawl collections during Decem-

ber, January, April, June, and August. Small larvae of either the blue-

7-23

back or American shad were collected in April with the sled at No Man's3

Friend Creek.

Other clupeid (herring) larvae which were identified as Atlantic

menhaden were collected in January, March, and April in both creeks.

Menhaden are one of the dominant species in the Winyah Bay area. In-

dividuals of all sizes occur from many miles into the ocean to theI

freshwater extreme of the estuary.

Spawning probably takes place in the fall. Some adults with roe

(eggs) were collected in gill nets in the creeks on the August and Sep-I

tember cruises. Egg release usually occurs in high salinity areas and

larvae move into estuarine nursery grounds (Nelson et al., 1977). Even

though juvenile menhaden are good swimmers which easily avoid nets,

many 50-150 mm fishes were taken in trawl collections in both creeks.

Hundreds of menhaden of the same size were caught in the fine mesh gill

nets during most cruises. Sometimes creek surface waters were darkened3

and agitated by schools of small menhaden. Hand seines and purse seines

are the most appropriate gear types for catching menhaden. Large com-

mercial purse seine fleets harvest tons of adult menhaden from waters

off of Winyah Bay each summer. Schools can be seen swimming near theI

surface year round, but the largest fishes migrate south along the coast3

as temperature declines. Nicholson (1978) described the dynamics of

populations along the coast.3

The ecological significance of menhaden in estuaries is great be-3

cause they filter microscopic algae and marsh plant detritus from the

water (Peters and Schaaf, 1981) and assimilate that energy into a form3

7-241

of protein which can be utilized by consumers higher in the food web.

Filter feeding menhaden may also influence zooplanktQn communities.

The migration of adult menhaden makes estuarine produced protein avail-

able to ocean predators, thus providing a crucial link between the pro-

ductive estuary and a relatively impoverished ocean. Menhaden consti-

tute major food sources for a variety of coastal fishes and birds.

Gizzard (Dorosoma cepedianwm) and threadfin (Dorosoma petenense)

shads were also collected at SJ. Juvenile (young of the year) shads

were taken in trawls in August and March. Adults of these commercially

unimportant shads live in low salinity and freshwater habitats. How-

ever, the young are tolerant of higher salinities an'd are frequently

taken in high marsh creeks and pools.

Anchovies are undoubtedly the most abundant schooling fishes in South

Carolina estuaries. Two species occurred in trawl collections at both

creeks. Because of their small size (<100 mm), neither species is ef-

fectively collected with the trawl. Adult bay anchovies (Anchoa mit-

chilli) were incidental catches in the trawl on every cruise. Striped

anchovies (Anchoa hepsetus) did not occur from January through April.

Larval and juvenile anchovies were collected with the epibenthic sled

every month of the year. During the warm months, densities of anchovy

eggs and larvae were very high in both sled and zooplankton collections.

Anchovies of all sizes are predators on planktonic and motile epi-

benthic crustaceans. Gut content analyses of small anchovies revealed

the presence of large numbers of copepods. Mysids and decapod larvae

were consumed by larger individuals. The diurnal movements and feeding

7-25

habits of bay anchovies in a local intertidal creek- are described by

Reis and Dean (1981). Anchovies comprised a major portion of the diet

of most large predators including bluefish, spotted seatrout, weakfish,

and summer flounder.

Inshore lizardfishes (Synodus foetens) are regular but not common

migrants to South Carolina estuaries during summer and fall. Individ-

uals from 80-290 mm in total length occurred from July through Novem-

ber in trawl collections at both creeks. Some lizardfish larvae (31-

36 mm) were taken in sled collections at both creeks in June. Spawning

probably occurs in the spring in nearshore coastal waters. Adult liz-

ardfishes remain partially buried in the substrate and attack small

fishes and, occasionally, shrimps.

Two marine catfishes were collected in SJ Creek. The less abundant

gafftopsail (Bagre marinus) (300 mm) was taken in gill nets in July.

Sea catfishes (Arius felis) were common from June through September,

but some small individuals were taken in trawls in January. Adults

were often observed brooding their eggs in their mouths. Sea catfishes

caught during the summer had penaeid shrimps, blue crabs, and fishes

(e.g. menhaden, spot, American eel) in their guts.

Oyster toadfishes (Opsanus tau) are resident demersal fishes in tem-

perate marsh creeks. Individuals from 20-290 mm occurred in trawls on

all cruises except January. During the cold months, toadfishes become

inactive and remain partially buried. More individuals were caught in

the spring and summer when they were feeding on crabs near the creek

bottom. Reproduction occurs in spring and summer. Eggs are attached

7-26

to hard bottom materials and the emerging young resemble the adult.

Skilletfishes (Gobiesox strwnumosus) occupy the same habitat as the

toadfishes, but this smaller species appears to be more abundant. A

sucking disk on the underside of the fish allows it to camouflage it-

self from small crustacean prey which also live among oyster clusters

and other obstructions. Small skilletfishes (<10 mm) were collected

with the sled during most of the year, but adults were not susceptible

to capture by the trawl.

The gadid family includes the familiar cold water groundfishes such

as cod, but two species of hakes were collected at No Man's Friend and

South Jones Creeks. Southern (Urophycis floridanus) and spotted (U.

regius) hakes (50-140 mm) were taken in trawls from January through

April. They were particularly abundant in SJ in April. Southern hakes

were somewhat more common. These epibenthic predators consumed large

numbers of mysids during the cold months. This observation is consis-

tent with the feeding habits of hakes in Georgia estuaries (Sikora et

al., 1972).

Striped cusk-eels (Rissola marginata) are peculiar fishes which spend

the daylight hours buried, tail first, in the bottom. Cusk eels were

usually caught at night while they were foraging on crustaceans near

the bottom. Some individuals were taken at both creeks from September

through April.

The killifishes are high marsh animals which rarely occur in major

creeks. One sheepshead minnow (Cyprinodon variegatus) was collected in

a January SJ Creek trawl. Young mummichogs (Fundulus heteroclitus) were

7-27

taken in sled tows during July, Larval Fundulus which could not be

identified to species occurred in summer sled collections. Killifishes

play a major role in the trophic dynamics of the estuary, especially

in marsh pools and creeks where they occur in very high densities.

Two species of silversides were incidental trawl catches in both

creeks. Adults of both of these narrow fishes are less than 130 mm in

total length and easily escape from the trawl net. During the warm

months, large schools of Atlantic silversides (Menidia menidia) occur

along creek banks and beaches. They tend to aggregate in deep channels

when water temperatures are low. All trawl catches of silversides were

between December and April. Larval rough silversides (Membras martinica)

were collected in the epibenthic sled at SJ.

Dusky (Syngnathus floridae), northern (S. fuscus) and chain (E. Zoui-

sianae) pipefishes were occasionally collected in both creeks. Because

of their shape and size, no reasonable estimate of their abundance could

be made with the trawl. Adults were taken from fall to spring. Juve-

niles occurred in sled collections during most of the year.

The sea basses were represented by two species in the creeks. Only

one small rock sea bass (Centropristes philadeZphica) was collected at

NMF. A total of eight gag groupers (Mycteroperca microlepis) were taken

at SJ from July through September. Both species were probably more abun-

dant than trawl catches indicated, because basses usually remain hidden

among bottom debris, and they are fast swimmers when disturbed. These

creeks are ideal habitats for young basses and groupers which enter the

high salinity marsh waterways as ocean spawned larvae each spring and

7-28

summer. Gag grouper larvae were fQund in June sled sanples,

Young bluefishes (Pomatomus saltatrix) were incidental trawl catches

in spring and summer at both creeks. These fast swimming pelagic pred-

ators are common in estuaries during most of the year, but most migrate

to the south along the coast in the winter. Adult bluefishes (260-360

mm) were frequently caught in gill nets from June through November. The

population dynamics and distribution of bluefish in coastal waters was

discussed by Kendall and Walford (1979).

One 86 mm juvenile cobia (Rachycentron canadum) was collected in a

trawl at SJ in July. Cobia are most abundant in tropical waters, but

individuals occur in South Carolina estuaries every year. In estuaries

in the southern part of the state, adult cobia are seasonal migrants

which support a popular sport fishery.

The carangids or jacks represent a large family of silvery fast swim-

ming warm water fishes. Juvenile crevalle jacks (Caranx hippos), Atlan-

tic bumpers (Chioroscombros chrysurus) and lookdowns (SeZlene vomer) were

taken in trawls at both creeks between June and September. Jacks are

not susceptible to capture by slow moving trawl nets, so juveniles may

be quite common in high salinity areas. Seine collections in North In-

let creeks indicate that these and many other species of jacks are com-

mon in the area. Young jacks eat a variety of invertebrates, but fishes

(e.g. anchovies, silversides) constitute the major dietary items.

Gray snappers (Lutjanus griseus) occurred in both creeks. One 55 mm

juvenile was collected with the trawl in September, and 13-15 mm larvae

were taken with the epibenthic sled in August. The larvae of this trop-

7-29

ical fish probably originate from southern coastal spawning areas. Gray

snappers are common in high salinity creeks in the summer. Numbers are

caught in traps and seine hauls in North Inlet creeks each summer.

Their habits are similar to those of the basses in that they remain

close to bottom obstructions and feed on small epibenthic animals.

Three mojarras were collected during the study. Although Irish pom-

panos (Diapterus olisthostomus), spotfin mojarras (Eucinostomus argen-

teus) and silver jennies (E. gula) were not abundant, Juveniles and

small adults were taken in trawls in both creeks from August through

November. Larvae occurred in sled samples in September and November.

These small (less than 100 mm) silvery fishes feed near the bottom of

major creeks, but appear to be more abundant in shallow high marsh

creeks and pools during summer and fall.

Small pigfishes (Orthopristis chrysoptera) were collected in July

and September. Larvae were taken with the sled in May and June at both

creeks. Although pigfishes are common shallow water fishes in the trop-

ics, relatively low numbers occur in South Carolina estuaries.

Two sparids or porgies, the sheepshead (Archosargus probatocephalus)

and the pinfish (Lagodon rhomboides) were collected at both creeks.

Young sheepsheads were caught in trawls in November, December and March

and were most abundant at SJ. This popular gamefish is common around

obstructions in estuaries and coastal waters. Larvae were caught in

the sled in June at NMF. One large adult (536 mm) was caught in a gill

net at SJ. Sheepsheads are year round residents which feed on molluscs,

barnacles and a variety of invertebrates associated with encrusting ben-

7-30

thIc communities. Pinfishes were the eighth most abundant species in

the trawl collections, None were caught in August, September and Jan-

uary; however, pinfishes are year-round residents of both, marsh-creeks.

Larvae were very abundant in sled samples from December through March,

Trawl caught individuals ranged from 25-180mm in length,

The sciaenid or drum family includes many of the most familiar estu-

arine food and game fishes. Collectively, the sciaenids probably ex-

ceed all other groups of inshore fishes except anchovies and mullets in

number and biomass (weight). Most species spawn near or in the ocean

and larvae migrate to estuarine habitats where they remain for up to one

year. Adults migrate to deeper and more southern areas during the winter.

Most species are fast growing and live less than three years. Eleven

species were caught in the study area and each is discussed below.

The silver perch (Bairdiella chrysura) does not grow large enough to

be a sport or food species. It was the fourth most abundant fish in the

trawl collections. Details of its seasonal and spatial distribution

with respect to numbers and biomass are given in Tables 7-2 and 7-3.

Young and adult silver perch were usually most abundant at SJ. They

were most common from July through November; however, the largest col-

lections were in March at SJ. Larvae were taken in sled samples from

May through September. Silver perch are predators of epibenthic crus-

taceans and fishes.

Spotted seatrout (Cynoscion nebulosus) (winter trout) are important

sport and commercial fishes in the Winyah Bay area, especially in the

fall and winter. Adults (265-420 mm) were caught in gill nets in both

Table 7-2. Numbers of individuals of the eight most abundant fishes in trawl collections at NMF and SJ
on all major cruises. Numbers are totals for all collections made during each cruise at
each creek.

AUG. SEPT. NOV. DEC. JAN. MAR. APR. JUNE JULY
SPECIES NMF SJ NMF SJ NMF SJ NMF SJ NMF SJ NMF SJ NMF SJ NMF SJ NMF SJ

Brevoortia tyrannu$ 18 20 i 13 0 0 0 1 I 2 0 7 2 27 20 185 9 3

~.j Anchoa mitohilli 568 2149 103 365 9 24 13 329 0 88 I 97 46 327 238 350 122 508
i

Bairdleila chrysura 16 58 17 18 5 40 I 12 0 2 0 179 3 8 2 0 0 16

Cynosoion regalis 26 36 0 9 0 i 0 0 0 0 0 0 0 0 3 35 51 45

Leiostomus xanthurus 837 528 42 340 31 185 15 11 0 12 158 505 198 309 175 248 351 299

Micropogoni~$ unduZatus 216 169 13 6 0 0 0 0 0 0 0 4 29 33 46 474 255 199

Trinettea maculatus 33 42 0 14 0 0 0 0 0 0 0 0 0 6 4 14 6 5

Symphurus pZagiusa 12 20 19 25 20 9 3 19 0 5 4 4 I 10 5 3 4 5

All others 71 257 37 92 27 30 25 50 36 47 48 59 66 125 14 41 33 52

Total fishes 1797 3279 232 882 92 289 57 422 37 156 211 855 345 845 507 1350 831 1132

Table 7-3. Weight in grams of individuals of the eight most abundant fishes in trawl collections at
NMF and SJ on all major cruises. Weights are totals for all collections made during each
cruise at each creek.

AUG. SEPT. NOV. DEC. JAN. MAR.
APR. JUNE JULY
SPECIES NMF SJ NMF SJ NMF SJ NMF SJ
NMF SJ NMF SJ NMF SJ NMF SJ NMF SJ

Brevoortia tyrannus 730 893 39 458 0 0 0 8 11 15 0 77 17 657 658 2894 193 22
r

Anchoa mitchilli 464 2411 t30 315 10 22 14 264 0 45 i 62
63 320 295 467 109 587

Bairdiellaohrysura 271 612 296 307 114 1389 39 659 0 25 0
3831 79 242 17 0 0 64

Cynoscion regalis 463 486 0 95 0 16 0 0 0 0 0
0 0 0 34 24 407 264

Leiostomus xanthurus 9103 7587 768 5568 526 2987 266 212 0 117
1789 10612 1119 6966 2098 3745 2748 2869

Mioropogonias undulatus 4130 3271 401 107 0 0 0 0 0 0
0 !69 581 750 1003 1678 2238 2270

Trineotes maoulatu$ 272 470 0 259 0 0 0 0 0 0 0
0 0 14 13 70 43 43

$ymphuru8 plagiusa 51 130 129 199 203 86 5 78 0 23
17 11 2 48 25 11 24
29

All others 2319 4381 782 2447 465 1838 130 578 142
225 383 1132 1489 2651 305 3348
294 1262

Total fishes 18074 20241 2545 9755 1318 6322 454 1799 153
1024 2190 15864 3350 11648 4447 12237 6056
7410

creeks in September and Noyember, In September, some females, which

had recently released their eggs were collected. Juveniles (<130 mm)

were incidental catches in trawls during most of the year. Larvae oc-

curred in sled collections in June and September in both creeks.

Spotted seatrout are dependent on estuaries as nursery grounds for the

young and adults do not make coastwide migrations like most other game-

fishes. Trawl records for seatrouts in other South Carolina estuaries

are given in Lunz and Schwartz (1970). Penaeid shrimps were most com-

monly found in the guts of gill net caught seatrout.

The weakfish (Cynoscion regalis) (summer trout) is a close relative

of the spotted seatrout. Adults were common in summer and early fall,

and juveniles were abundant in trawls from June through November. De-

spite its being a fast swimmer, the weakfish was the sixth most abundant

species in the trawl study (Table 7-2). Epibenthic sled collections pro-

duced larvae from May through September. Weakfishes are caught by local

anglers and considered a fine food and sport fish. It is a major com-

mercial species in northern estuaries. Foods include shrimps and small

fishes.

The spot (Leiostomus xanthurus) is one of the dominant fishes in east

and Gulf coast estuaries. In this study, spot ranked second to ancho-

vies in terms of numbers of individuals (Table 7-2) and exceeded all

other species in weight on every cruise (Table 7-3). On many tows,

hundreds of juvenile spot were collected, and one SJ collection yielded

more than 700 individuals. Spot were most abundant from March through

September, and, although winter densities were low, spot were only ab-

sent in January at NMF.

7-34

Adult spot spawn in the ocean in the late fall, and the migration of

high densities of larvae into the estuary each winter is very distinct,

Larvae from 11-15 mm in total length first occurred in sled samples in

January, and at least a few were collected in almost every sled tow at

both creeks through June,

The length frequency analysis for spot catches on all cruises is il-

lustrated in Fig. 7-6. Most individuals collected from August through

November (80-130 mm total length) were spawned the previous fall. Young

of the year larvae were not retained by the trawl in January collections,

and their presence was not detected in trawl samples until they were

more than 20 mm in length in March. Most of these young were in the

30-70 mm range in June and 60-100 mm range in July. The presence of

100-140 mm individuals from March to June is probably due to the greater

susceptibility to capture of fishes of this size relative to larger in-

dividuals. Large spot avoid trawl nets and appear to occupy flat bot-

toms in Winyah Bay and shallow ocean areas instead of marsh creeks.

Dawson (1958) gives a thorough account of the life history and ecol-

ogy of the spot. More recent studies by Chao and Musick (1977), Wein-

stein (1979), Hodson et al.(1981) and Weinstein and Walters (1981) have

greatly contributed to our understanding of this important species.

Three species of kingfish or whiting were collected at SJ. Adult

northern (Menticirrhus saxatilis), southern (M. omericana), and Gulf

(M. littoralis) whiting were caught in gill nets in the summer and fall.

Juvenile whiting (less than 150 mm) were incidental in trawl catches at

the same time. Larval southern kingfish occurred in sled collections

7-35

225- Aug Mar
Mar

75,

75 -

225
Apr
225 -
Sep
75 '
co 75-

75 cIl!

E Jun
Z 75 -
Nov
75-

225
Jul
30 Dec J

30o J a n .

20 40 60 80 100 120 140 160 180 200 20 40 60 80 to100 120 140 160 180 200

Length In Millimeters

Figure 7-6. Length frequency analysis of spot (Leiostomus xanthurus) in trawl collections on major
cruises at NMF and SJ. Height of each bar indicates total number of spot of that size
class at both creeks. Shaded portion of each bar represents number collected at NMF.

in June and August at SJ. All three species are most common in high

salinity areas, especially along beaches where they are caught by an-

glers. Whiting species are difficult to distinguish from one another.

Bearden (1963) reported that southern kingfish were the most common of

the three species in subtidal estuarine areas in South Carolina,

The Atlantic croaker (Micropogonias undulatus) was the third most

abundant fish in both creeks. More than 1400 juvenile and small adult

croakers were collected from March through September (Table 7-2). This

popular sport and food fish was represented by larvae and small juve-

niles in the sled samples on every cruise except May and July. Large

adults are not common in this section of the croaker's long geographical

range, but South Carolina estuaries are very important nursery areas for

this species.

The length frequency analysis for all croaker collected with the trawl

is given in Fig. 7-7. Large numbers of 110-140 mm fishes were present

in August, but most left the area before the September cruise. Two

year classes were recognized in April and June when the creeks were

repopulated by a migrating population. Young of the year which spawned

in the ocean in the fall and winter were first apparent as 30-50 mm ju-

veniles in the June trawls. Bearden (1964) suggests that smaller fish

occur in low salinity areas and that an average length of 150 mm is

typical for a one year old fish.

Juvenile black drum (Pogonias chromis) (<150 mm) were collected in

August and September. Little is known about the spawning and distribu-

tion of this species in the Winyah Bay area. Small adults are often

7-37

90 -

Jun
150- Aug

90- ~~~~~~~~~~~~~~~~~30

(, .10-3Jul
30- 210-

Sep 150 -

Mar 90

o~30 o'Apr 30

20 40 620o 2140160 180 200 204 O8; o 40 60 80 ' I1046 o'180200

Length In Millimeters

Figure 7-7. Length frequency analysis of Atlantic croaker (Micropogonias undulatus) in trawl
collections on major cruises at NMF and SJ. Height of each bar indicates total
number of croaker of that size class at both creeks. Shaded portion of each
bar represents number collected at NMF.

- m m_ - m1 - -m

caught around obstructions by anglers seeking sheepshead.

Red drum (Sciaenops ocellata) (spot tail or channel bass) are one of

the most popular gamefishes in the southeast and Gulf states. Although

adults from I to 50 pounds in weight are caught in the surf and in cer-

tain marsh creeks, none were collected in gill nets or trawls. Juve-

niles (< 100 mm) were taken in November, January and March. Larvae

(4-10 nmm) occurred in sled samples from August through October, Red

drum are year-round residents of the high salinity marshes. Young eat

a variety of crustaceans and fishes. The guts of adults caught along

marsh banks usually contain fiddler crabs.

The star drum (stellifer lanceolatus) is a small, little-known sci-

aenid of temperate and subtropical estuaries. Sled collections in both

creeks in early summer yielded 3-4 mm larvae and, although these early

life stages were also present in August, some small juveniles (<40 mm)

were collected. No star drum were caught in trawls at either creek.

Spadefishes (Chaetodipterus faber) were collected in August, Septem-

ber, and November at both creeks. They were most abundant in August

when most individuals were 30-70 mm in total length. Juvenile spade-

fishes are common in high salinity areas during the summer after migrat-

ing from remote spawning areas. No larvae were collected with the sled.

Two species of mullet were abundant in the creeks. Schools of white

mullet (Mugil cephalus) juveniles and adults are ubiquitous in the Win-

yah Bay area. These fast swimming schooling fishes occur with menhaden

in the surface waters, especially from spring through fall. Some juve-

niles (<100 mm) were incidental catches in trawls from July through Sep-

7-39

tember. Adults are caught in seines and gill nets during this period.

Striped mullet (Mugil cephalus) are less common; some juveniles occurred

in November and December. Ovigerous female adults of both species were

taken in the fall and small juveniles occurred in sled samples in Jan-

uary. Large schools of small juveniles (<30 mm) were observed swimming

near the surface under lights in winter and spring. Anderson (1957 and

1958) described the early life history and distribution of both species

on the southeast coast.

Mullet feed on organic particles and small invertebrates (Collins,

1981). They are widely distributed in estuaries and appear to be very

tolerant of temperature and salinity fluctuations. From an energy

standpoint, they are important assimilators of marsh production which

is not utilized by other large organisms. Mullets are major food sources

for predators such as gars, spotted seatrouts, bluefishes and flounders.

Feather blennies (Hypsoblennius hentzi) (20-80 mm) were collected in

trawl nets in November and January. Larvae were taken in October and

June. The only other blenny collected was the striped blenny (Chasmodes

bosquianius) which occurred as larvae in August sled samples. Both spe-

cies are abundant in the creeks and throughout the high salinity coastal

areas, but their cryptic benthic life styles and small sizes prevent

them from being caught in trawls. Blennies are predators of small crus-

taceans and other invertebrates.

Gobies are even more abundant on creek bottoms than blennies. Darter,

sharptail, freshwater, naked, seaboard, clown and green goby larvae and

small juveniles were identified in sled collections, but only a few

7-40

adult naked (Gobiosoma bosci) and a single sharptail CGobione74us

nastatus) adult were taken with the trawl. Since none of the seven

species is trawl susceptible, assessments of their relative abundance

were not possible. However, the abundance of larvae from June through

October indicated that large numbers of these year-round residents were

present. Gobies inhabit irregular shell and debris-laden bottoms and

were much more common in SJ than NMF.

A single 140 mm juvenile spanish mackerel (Scomberomorus maculatus)

was taken in a trawl at SJ on the August cruise. This common gamefish

was probably a stray visitor from adjacent ocean waters, although the

presence of numbers of small mackerel in the estuary could not be de-

tected with trawls or gill nets.

One juvenile harvestfish (Peprilus alepidotus) and one juvenile but-

terfish (Peprilus triacanthus) were collected in August trawls at SJ.

These fast-swimming pelagic fishes utilize high salinity estuarine

areas as nursery grounds. Small individuals migrate from ocean spawning

grounds in the summer.

Juvenile bighead searobins (Prionotus tribulus) occurred from January

through June. Greatest numbers were taken at both creeks in May when

40-80 mm juveniles were present. Larvae were collected with the sled

in April, June and August. Other species of searobins are common in

North Inlet creeks during the summer.

Seven species of flatfishes representing three families occurred in

trawl collections. Juvenile ocellated flounders (Ancyclopsetta quadro-

ceZZllata) were caught in trawls from March through June. Ocellated

7-41

flounder larvae were not collected with the sled. Juveniles and small

adult bay whiffs (Citharichthys spilopterus) occurred from Ouly through

December, and larvae were taken in sled tows in December and March.

Fringed flounders (Etropus crossotus) were common at both creeks from

June through December, and larvae were taken in sled tows in December

and March. Flounders less than 40 mm in total length were not suscep-

tible to capture with the trawls, and it is likely that fringed and

other small flounders were much more abundant than the trawl data in-

dicated.

The summer (Paralichthys dentatus) and southern (P. Zethostigma)

flounders are favorite sport and commercial species in coastal waters.

The two species are difficult for fishermen to separate, but the south-

ern flounder was much more abundant than the summer flounder in the

study area. Young flounders (<180 mm) were collected with the trawl

on all but the August cruise. Southern flounders were most abundant

from December through March. A few summer flounder juveniles were

taken in spring and fall. The adults of both species migrate to deep

ocean spawning grounds in the fall. Larvae of both species arrive in

the estuary in December, and were caught in sled samples at both creeks

until May. Young summer and southern flounders inhabit brackish and

high salinity areas where they prey on crustaceans and fishes. Adults

migrate back to inshore waters in the spring and remain until fall. The

inshore distribution of paralichthid flounders in North Carolina estu-

aries is discussed by Powell and Schwartz (1977). Southern flounder

were the more abundant of the two species in gill net catches from June

through September.

7-42

Hogchokers (Thinectes maculatus) were the second most abundant flat-

fishes in the collections. These medium size flounders occurred from April

through September and were particularly abundant in August (Table 7-2).

They were usually more common at SJ and, although large numbers occurred

at SJ in September, none occurred at NMF on that cruise. Hogchoker larvae

were taken with the sled from June through August. Hogchokers occur on mud

and sand bottoms from the ocean to freshwater extremes of South Carolina

estuaries. They consume polychaete worms and soft-bodied invertebrates.

Hogchokers have no commercial value and have not been found in the guts of

any other fishes.

Blackcheek tonguefishes (Symphurus ptagiusa) were the most abundant

flatfishes and the seventh most abundant species in the creeks (Table 7-2).

Juvenile and small adult tonguefishes (20 - 90 mm) were collected on every

cruise, but were most abundant from August through November. Larvae and

small juveniles occurred in sled collections in all months except February,

April, May and June. Small tonguefishes are common throughout the surround-

ing area during the warm months. They are not effectively sampled with a

trawl.

One juvenile (17 mm) planehead filefish (Monacanthus hispidus) was

collected in a November SJ collection. Juvenile filefishes migrate from

tropical spawning areas in the summer, and in some years are abundant in

South Carolina estuaries.

Larval northern puffers (Sphoeroides maculatus) (10 - 12 mm) were col-

lected in the sled at NMF in June and August. Young puffers take up resi-

dence in high salinity areas after migrating from ocean spawning

7-43

grounds. Adult puffers were not collected in the trawl study and appear3

to be rare in the Winyah Bay area,

B. FTSH COMMUNITIES

The otter trawl is one of the most widely used net designs for cap-
turing fishes in subtidal areas, but it is inadequate for the collection

of the majority of species which inhabit estuarine waters. Seines, gill

nets, beam trawls, and sleds also have limited applications in the char-I

acterization of the fish fauna. Collections made with nets never pro-

vide accurate measures of the abundance of any species; however, valu-

able information on community composition and population structure (e.g.j

length frequency) can be obtained. Since there are few practical al-

ternative methods of quantifying fishes which yield more accurate in-I

formation, studies which utilize a particular gear at regular intervals

at specific locations must be relied upon to provide the information.

Consistency in sampling is necessary. Relative abundance data are used

to determine temporal variation for some species and, to a lesser extent,

to describe species diversity.

In the trawl study at NMF and SJ Creeks, 65 species of fishes were

taken in 41 trawl tows on 9 cruises. More than 13,300 fishes were iden-

tified to species and most of them were measured and weighed. The eightI

most abundant species accounted for 92% of the total number of fishes5

collected in the trawl study (Table 7-2). These eight species also

accounted for 81% of the total weight (biomass) of all fishes caught3

in the program (Table 7-3). Figure 7-8 shows the total number of fishes

collected on each cruise. Maximum numbers at both creeksL occurred in

7-441

ENMF
3000 N

DsJ

2000

Month Aug Sep Nov Dec Jan Mar Apr JunJu

Figure 7-8. Total numbers of all fishes in trawl collections on major cruises. First column of each
couplet indicates numbers for NNF, second column for $J.

August. Fish abundance decreased in September and November, remained

low through January, increased abruptly in March, and continued to in-

crease slightly through July. A similar pattern was observed for total

weight of all fishes collected on each cruise (Fig. 7-9). The abrupt

increase in fish weight in March indicates that the fishes which were

in SJ in March were larger than those present in January. The fishes

in NMF in August were larger than those in SJ.

One way to examine changes in the composition of fish communities is

to use diversity indices. The three indices used to analyze the trawl

data are described in Table 7-4 and the results of the analyses are in

Table 7-5.

At NMF, all three indices showed that diversity increased from August

to an annual peak in November from which it declined to the annual low

in January (Table 7-5). Diversity increased in March and April, de-

creased slightly in June and reached August value levels in July. In

summary, despite relatively low total numbers of fishes at NMF in Novem-

ber, a large number of species were represented. Many warm water migra-

tory species occurred in the marsh creeks in the fall.

The three diversity indices followed a different seasonal pattern at

SJ Creek (Table 7-5). While the species richness values were at the

annual maximum in September, the evenness index was at one of the lowest

values of the year. All indices decreased in December. Large increases

were seen in J and H' in January and, after a slight decrease in March,

levels returned to January levels through July,

In general, values for the diversity indices at NMF and SJ were high-

7-46

E NMF

20,000 -
DSiJ

16,000 -

E
X 12,000-

LL
0
tD
e

8ooo -
.?

0 8000-

4000 -

Month Aug Sep Nov Dec Jan Mar Apr Jun Jul

Figure 7-9. Total weights of all fishes in trawl collections on major cruises. First column of each
couplet indicates numbers for NMF, second column for SJ.

Table 7-4. Diversity indices used for fish community analysis.

1. Species richness component (Marqalef, 1968 and Dahlberg and Odum, 1970)

D = (S-1)/loge Nm where S = number of species and N = number of

individuals

2. Shannon-Weaver function (Bechtel and Copeland, 1970, and Dahlberq and

Odum, 1970)

H' = - Pi loge Pi, where Pi is the proportion of individuals in

the ith species

3. Evenness index (Pielou, 1966)

J = H'/loge S

7-48

Table 7-5 . Values for fish diversity indices at NMF and SJ Creeks.
Abbreviations are: S = number of species; N = number of
individuals; D = species richness index; H'= Shannon-
Weaver function; and J : evenness index.

No Man's Friend Creek
MONTH S N D H' J

Aug 19 1797 5.53 0.62 0.49
Sep 16 232 6.34 0.79 0.66
Nov 15 92 7.13 0.90 0.77
Dec 10 57 5.13 0.76 0.76
Jan 6 37 3.19 0.33 0.43
Mar 14 211 5.59 0.47 0.41
Apr 17 345 6.31 0.67 0.55
Jun 17 507 5.92 0.59 0.48
Jul 17 831 5.48 0.65 0.53

South Jones Creek
Aug 34 3280 9.39 0.64 0.42
Sep 30 882 9.85 0.71 0.48
Nov 19 289 7.31 0.60 0.47
Dec 16 422 5.71 0.44 0.36
Jan 16 156 6.84 0.75 0.62
Mar 16 855 5.12 0.56 0.46
Apr 17 845 5.47 0.72 0.58
Jun 17 1350 5.11 0.70 0.57
Jul 21 1132 6.55 0.66 0.50

7-49

er than those reported for other salt marsh creeks (CWjn ond Dean, 1976;

Subrahmanyam and Coultas, 1980).

A comparison of NMF and SJ Creeks indicated that maximum diversity

occurred earlier in the fall at SJ and that diversity was somewhat

greater at SO than NMF. The most striking difference between the two

creeks was the much greater values for all three indices at SJ in Jan-

uary (Table 7-5). Small sample size such as the low total number values

for January is known to affect the calculation of various indices

(Pielou, 1977).

Declines in diversity between the fall maximum and winter minimum are

related to the migration of many warm water species from the estuary.

Similar decreases were observed for the fish fauna of an intertidal
creek in North Inlet (Cain and Dean, 1976) and Winyah Bay (Wenner et

al., 1980).

At least 33 of the 85 species collected with all gear at NMF and SJ

are year-round residents of the creeks and adjacent high salinity areas.

The majority of the migratory species arrived in the summer and fall,

although some (e.g., the hakes) entered shallow creeks in the winter.

The total numbers and weights of fishes at SO were always greater

than those at NMF (Fig. 7-8 and 7-9). This pattern is consistent for

all of the most abundant species of fishes. Bay anchovies were 3.9

times and pinfish were 4.2 times more abundant at SO. Silver perch,

spot, menhaden, croakers, southern flounders, tonguefishes, hogchokers,

and spotted seatrout were also more abundant at SO. Of the 65 species

7-50

caught in the trawl, only silversides, bighead searobins and cusk eels

were more conmmon at NMF than SJ Creek. Only 4 species were collected

exclusively at NMF, while 23 species occurred only at SJ. Fishes which

were collected at SJ only were either more typical of ocean habitats

(e.g., cobia, whitings, butterfishes, harvestfishes, and Spanish mack-

erel) or more common on irregular subtidal habitats (e.g. eels, blen-

nies, gobies, groupers and snappers). Despite the high and roughly

equivalent salinities at both creeks on all cruises, the closer proxim-

ity of SJ to the ocean indicates a closer association than NMF to the

sea. Additionally, the more complex bathymetry and well developed

sessile benthic communities at SJ provide a greater number of habitats

for fishes and their prey.

The results of the trawl study in NMF and SJ can be compared to

other trawl surveys in South Carolina estuaries. A 12-month survey near

Prince Inlet yielded 67 species (Bears Bluff Labs, 1965). Spot, croak-

ers, hogchokers, tonguefishes, and flounders accounted for the largest

portion of the catch. One major difference between the two studies is

the occurrence of the star drum as a major species at Prince Inlet.

Sandifer et al. (1980) summarized the results of studies conducted by

South Carolina Marine Resources Research Institute (Charleston) in sev-

eral estuaries from 1975-1978. In a trawl survey of the nearby Santee

Estuary, a record number of species (77) were collected. Low salinity

areas were sampled and white catfishes comprised a major part of the

catch. High salinity species assemblages were similar to those at NMF

and SJ.

7-51

Shealy et al.(1974) reported that 88 species of fishes were caught

in trawls at 33 stations in estuaries from Winyah Bay to Caliboque

Sound. All stations were sampled at least quarterly for 212 months.I

Croaker and spot dominated most collections.3

Wenner et al. (1980) conducted monthly trawls at nine stations in

W~inyah Say from January 1977 to December 1978. Stations were located

in the channel from the lower bay lighthouse to the freshwater reaches

of all four rivers feeding the estuary. A total of' 77 species of fishes

were collected in 216 collections. The dimensions of the trawl and its

net size were larger than the device used in the NMF-SJ study; however,

similar seasonal changes in fish diversity were observed. Other simi-I

larities in the results of the two studies include the dominance of

juvenile fishes at all stations and the importance of relatively few

species. In Winyah Bay, seven species comprised more than 90% of the3

total numbers. Among the high salinity species, all but the star drum

were also dominants at NMF and SJ. In fact, the star drum was the most3

abundant fish in the Winyah Bay study, It is not known whether the ma-5

jor difference in the abundance of star drum in the two studies is re-

lated to year to year fluctuations in population sizes or to the general3

distribution of the species within the estuary. Several other species

which were fairly common in Winyah Bay were not collected at NMF andI

SJ; these include the black sea bass, Atlantic thread herring, banded3

drum, windowpane and striped bass. Commercial gill nets set in Mud Bay

catch large numbers of small adult striped bass, red drum, and, when sal-5

inities are depressed by high river discharges, yellow bullheads. Young

Atlantic and shortnose sturgeons also regularly occur in qill net setsI

7-521

in Mud Bay adjacent to NMF and SJ, but none were collected in this

study.

In summary, NMF and SJ are populated by large numbers of finfishes,

most of which are juveniles. The diversity and abundance of fishes,

especially during the summer, indicates that these creeks are very im-

portant nursery areas for coastal species. Almost all of the species

which are of commercial and recreational significance in Southt Carolina

occurred at the creeks. The majority of these species were represented

by postlarval or young juveniles which had migrated from remote spawn-

ing locations to marsh creek habitats which provided rich food supplies

and shelter from larger predators.

7-53

CHAPTER 8. REPTILES, BIRDS AND MAMMALS

Reptiles, birds, and mammals were not censused or collected in the

NMF or SJ areas, yet they constitute major components of the salt marsh and

estuarine ecosystems. Observations on the occurrence of the various species

are reported in this chapter. More complete information on the distribution

and abundance of these animals is found in Sandifer et al. (1980).

Only one reptile, the diamondback terrapin was common in the creeks

during the study. The race recocnized in South Carolina waters is known as

Malaclemys terrapin centrata. This turtle is one of the world's few

estuarine reptiles, since it completes its entire life cycle in brackish

and high salinity marsh areas. Coker (1906) observed that diamondback

terrapins could live in freshwater for long periods, but they are most

abundant in the lower estuaries.

According to Hildebrand (1932), terrapins may reach sexual maturity

at six years of age and live for more than 40 years. Females move to

sandy high marsh and beach areas to deposit eggs in shallow nests. In

N rth Carolina marshes, young turtles hatch in about eight weeks (Hay,

1917).

Diamondback terrapins feed on or near the marsh surface where they

consume fiddler crabs (Uca spr.) and snails (Littorina spp. and Melampus

spp.). Hurd et al. (1979) reported on the feeding behavior and aspects

8-1

of the biology of the terrapin in Delaware marshes.I

Terrapins were observed in the creeks from April through November, but

no evidence of their presence was found during the coldest months. In the

northern section of their coastwide range, terrapins hibernate in the mud

along creek banks (Yearicks et al., 1981). Although hibernating terrapins

have not been found in the study area, it is likely that they become dor-I

mant during the winter. Huge numbers of terrapins abruptly appear in the

creeks each spring.

Other turtles occur in Winyah Bay, NMF, and SJ from spring throughI

fall, but they are not common. The loggerhead, green and Kemp's Ridley3

sea turtles occur seasonally in South Carolina coastal waters. Leather-

backs and hawksbills have been taken in offshore waters, but are much3

rarer. Dead turtles are often washed into the surf at North and Debidue

Islands, and loggerhead and juvenile green turtles have been observed andI

collected from North Inlet creeks (Talbert, personal communication). Sea3

turtles may use estuarine areas for feeding grounds more frequently than

casual observations may indicate.3

Loggerhead turtles (Caretta caretta) were seen in NMF and SJ in the3

summer and fall, and are known to nest on beaches bordering lower Winyah

Bay (Stancyk, Talbert, and Miller, 1979). Nesting is especially dense on5

the oceanward beaches of the islands adjacent to Winyah Bay (North Island,

Sand Island, South Island). Nesting also occurs on the parts of those

islands forming the mouth of the bay, as well as on the sand beach of South3

Island within the bay. Loggerheads occur throughout the warm months in

8-23

both Winyah Bay and the tidal creeks. .]uveniles, which feed on bottom

invertebrates, are especially abundant. Adults may occupy large bays

between nestings, and have entered Winyah and Rom~in Bays while being

radiotracked (S. Hopkins and T. Murphy, personal communication).

The American alligator (Alligator mississippiensis) occasionally occurs

in high salinity estuarine waters, but are more common in old ricefields and

freshwater marshes. Alligators have been observed in No Man's Friend Creek

and along the edges of Mud Bay marshes. Nesting occurs on higher ground.

Alligators become dormant during the coldest months. In South Carolina,

alligators are protected by special regulations (Sandifer et al., 1980).

At least five species of snakes are known to occur in estuarine

marshes and waterways. The eastern cottonmouth (Agkistrodon piscivorous),

canebrake rattlesnake (Crotalus horridus), and three species of water snakes,

(Natrix spp.) are primarily freshwater marsh and swamp inhabitants, but are

known to wander in brackish and salt marsh areas. None were observed at

NMF, SJ or Winyah Bay during this study.

Birds are, of course, the most conspicuous and abundant higher animals

occurring in the study area. Numbers, species composition, and space use

patterns are not well documented; however, a considerable amount of reli-

able and useful information has been gathered by Baruch Institute re-

searchers (R. Christy, P. DeCoursey, K. Bildstein, and P. Frederick) and

S.C. Wildlife, and Wildlife and Marine Resources Department personnel

(J. Cely and P. Wilkinson). Sandifer et al. (1980) provides a summary of

the literature pertaining to South Carolina coastal birds.

8-3

Christy, Bildstein, and DeCoursey (1981) reported bird census figures

for the NMF and SJ areas based on biweekly surveys with an airplane from

August 1978 to September 1980. Information on the birds on the huge Pump-

kinseed Island rookery adjacent to SJ Creek (Fig. 1-1) has been collected

since 1974 by some investigators. This relatively large isolated nesting

ground for colonial wading birds supports up to 44,000 individuals at the

peak of the nesting season.

A checklist of birds known to occur in the creeks and marshes of the

study area is given in Table 8-1. From spring to fall many species of

shorebirds feed on the vast intertidal mud flats which surround Mud Bay,

while other species of water birds dive after fishes and macroinvertebrates.

Large numbers of ducks feed and raft in the relatively undisturbed

Mud Bay area, especially during the winter. The majority of water birds

using the study area are migratory forms, but many resident species occur.

The eastern brown pelican (Pelicanus occidentalis) is one of the most

frequently sighted birds in the study area. Individuals or small flocks of

pelicans feed from the brackish portion of Winyah Bay to many miles off the

coast during most of the year. Often groups of hundreds of birds can be

seen standing on sandy shores. During our sampling cruises, pelicans fed

on schools of mullet and menhaden in the creeks. The eastern brown pelican

is an endangered species in South Carolina and the nation, and the popula-

tion on this part of the coast is one of the largest surviving (Sandifer

et al., 1980).

The American peregrine falcon (Falco peregrinus) also has endangered

status on the state and federal lists. There have been confirmed sightings

8-4

of this seasonal migrant by Baruch Institute personnel on North Island,

North Jones Creek, and Goat Island in the North Inlet area on several

occasions.

The southern bald eagle (Heliaeetus leucocephalus) is another endang-

ered bird which is commonly sighted in the study area. An active nest

of this resident fish-eating bird of prey is located on the Thomas Yawkey

Wildlife Center on the south shore of Winyah Bay, and juveniles have been

observed feeding in the channel near our Esterville Plantation station

(T. Murphy, personnel communication).

Raccoons (Procyon lotor solutus) are common around marsh creeks which

are adjacent to terrestrial areas. At NMF raccoons were observed swimming

in the creek and feeding on crabs and mussels (clams) on the marsh surface.

Raccoons probably use marshes for feeding grounds only, since nesting

usually occurs in trees. Aspects of the ecology of raccoons in South

Carolina estuaries are summarized by Sandifer et al. (1980).

River otters (Lutra canadensis Zataxina) were observed in NMF in

August. These mammals are more aquatic than raccoons and Wilson (1954)

suggests that they are carnivorous animals which are more dependent on

fishes and swimming crabs than other marsh animals.

The occurrence of rabbits, voles, deer, and rice rats on estuarine

marshes are discussed by Sandifer et al. (1980).

The Atlantic bottle-nosed dolphin (Tursiops truncatus) or porpoise,

was commonly observed in NMF and SJ. Johnson et al. (1974) and Sanders

(1978) claim that this porpoise is the only resident marine mammal in

8-5

I
South Carolina waters. Porpoises are usually seen in small groups
throughout North Inlet and Winyah Bay year-round. Indvidua1s are some-
times observed leaving the water to slide onto the marsh surface, presum- 3
ably to catch an emerqent turtle, crab, or fish.
I
I
I
I
I
I
I
I
I
I
I
I
I
I
8-6

Table 8-1. Checklist of birds known to use Mud Bay and surrounding
creeks and marshes.

Common Loon Sora
Red-throated Loon Common Gallinule
Red-necked Grebe American Coot
Horned Grebe American Oystercatcher
Brown Pelican American Avocet
Double-crested Cormorant Semipalmated Plover
Great Blue Heron Black-bellied Plover
Green Heron Marbled Godwit
Little Blue Heron Whimbrel
Cattle Egret Yellowlegs
Great Egret Willet
Snowy Egret Spotted Sandpiper
Louisiana Heron Ruddy Turnstone
Black-crowned Heron Dowitcher
Yellow-crowned Heron Semipalmated Sandpiper
Least Bittern Western Sandpiper
Wood Stork Least Sandpiper
Glossy Ibis Dunlin
White Ibis Herring Gull
Mallard Ring-billed Gull
Black Duck Laughing Gull
Gadwal 1 Bonaparte's Gull
Common Pintail Gull-billed Tern
American Widgeon Forster's Tern
Redhead Common Tern
Canvasback Little Tern
Scaup Royal Tern
Common Goldeneye Sandwich Tern
Bufflehead Caspian Tern
Ruddy Duck Black Tern
Red-breasted Merganser Black Skimmer
Hooded Merganser Barred Owl
Turkey Vulture Short-earred Owl
Black Vulture Common Nighthawk
Red-tailed Hawk Belted Kingfisher
Bald Eagle Tree Swallow
Northern Harrier Rough-winged Swallow
Osprey Barn Swallow
Peregrine Falcon Fish Crow
Merlin Marsh Wren
American Kestral Red-winged Blackbird
Clapper Rail Boat-tailed Grackle
Virginia Rail

8-7

CHAPTER 9. WINYAH BAY: 1980-81 CRUISES

Although the primary thrust of the research discussed in this report

was to quantify physical and biological aspects of the exchange areas be-

tween Winyah Bay and North Inlet (No Man's Friend and South Jones Creeks),

samples were also taken regularly at several stations in Winyah Bay to

provide background information for subsequent, more intensive studies of

the Bay. The six permanent stations in Winyah Bay are described in Chapter

1, and sampling methods for physical and chemical parameters, zooplankton,

and epibenthos are described in Chapter 2. These stations were not sampled

as extensively as the NMF and SJ sites, and the data provide only a general

description of the characteristics of the bay.

A. CVEMCAL AND PHYSICAL MEASUREMENTS

Due to the nature of the sampling schedule in Winyah Bay, intensive

analysis of chemical nutrient availability was not performed. Basic phys-

ical parameters were recorded at each station to provide a general under-

standing of observed differences in densities of zooplankton and epibenthos

between the six stations.

Surface water temperatures (Table 9-1) for the Winyah Bay sampling

sites ranged from 6.0 to 31.30C. Bottom water temperatures ranged from

6.3 to 32.80C. Lowest temperatures were recorded in February and highest

9-1

temperatures were observed during July and August. Only minor differences

in surface and bottom water temperatures were noted between stations.

Water temperatures generally increased from February minima to July and

August maxima and steadily declined thereafter.

Surface and bottom salinities (Table 9-1) showed wide fluctuations

between stations and sampling dates, but no seasonal trends were discern-

able. Salinities ranged from 0.0 to 34.2 o/oo in surface samples and from

0.9 to 35.2 o/oo in bottom samples. Surface and bottom salinity values

were most similar in the three lower Winyah Bay stations (Mother Norton,

Mud Bay and Esterville Plantation). Surface salinities for the lower sta-

tions ranged from 10.3 to 34.2 o/00 and bottom salinities ranged from 11.1

to 35.2 o/oo. Surface and bottom salinities were also similar for the

three upper bay or river stations (Sampit River, Pee Dee River, and Wacca-

maw River). Surface salinities for these stations ranged from 0.0 to 12.1

o/oo, and bottom salinities ranged from 0.9 to 17.3 o/oo. Surface and

bottom salinities in the Sampit River were generally higher than salinities

recorded in the Pee Dee and Waccamaw Rivers. Higher salinities in Sampit

River water samples reflected the negligible freshwater inflow to Winyah

Bay from this source (Trawle and Boland, 1979). Although surface and bottom

salinities at a particular station and sampling date rarely differed by more

than 10 o/oo, salinity of bottom water was usually greater than surface sal-

initv at each station during all sampling periods. Surface and bottom sal-

inity differences were expected because of the dominance of the flood flow

at the bottom and dominance of the ebb flow at the surface during all flow

conditions (Trawle and Boland, 1979).

Secchi disk visibility for the Winyah Bay stations ranged from 0.25m -

9-2

Table 9-1 Physical and chemical characteristics of water samples col-
lected in Winyah Bay, South Carolina during August, 1980
through July, 1981.

ESTERVILLE PLANTATION
Cruise No. 1 3 5 7 9 11 13 15 17
Month AUG SEP NOV DEC FEB MAR APR JUN JUL

Water Temperature(�C)
Surface 31.0 28.8 16.9 10.6 6.0 14.0 21.4 27.3 28.5
Bottom 29.4 28.8 17.0 10.7 6.3 12.5 21.0 27.0 28.3

Salinity (o/oo)
Surface 16.9 29.6 23.5 12.4 29.7 20.0 11.6 10.3 15.7
Bottom 23.9 30.2 27.6 12.4 30.1 30.6 16.1 11.1 22.5

Secchi Disk (m) 0.65 0.65 0.65 0.35 0.45 0.45 0.35 0.55 0.75

Air Temperature (OC) 26.0 29.0 19.0 18.0 0.0 12.0 24.0 27.0 27.0

MUO BAY
Water Temperature(oC)
Surface 30.9 29.2 17.2 10.6 6.0 13.2 21.3 27.4 28.7
Bottom 30.3 29.2 17.4 10.6 6.7 12.5 22.4 27.3 27.8

Salinity (o/oo)
Surface 18.4 28.1 20.3 19.6 20.8 29.0 20.7 21.2 20.2
Bottom 18.9 28.8 20.0 20.7 27.6 31.7 17.4 11.9 26.3

Secchi Disk (m) 0.55 0.55 0.45 0.55 0.45 0.55 0.35 0.25 0.65

Air Temperature (�C) 25.5 31.0 21.0 14.0 0.0 13.0 22.0 28.0 29.0

MOTHER NORTON

Water Temperature(�C)
Surface 30.7 28.7 17.3 11.6 6.0 12.7 20.3 26.8 27.3
Bottom 30.3 28.6 17.0 11.8 6.6 12.7 19.3 26.6 25.8

Salinity (o/oo)
Surface 28.9 34.2 32.3 33.3 31.3 32.6 31.5 27.2 33.0
Bottom 29.3 34.3 32.0 33.3 33.4 32.8 32.4 29.3 35.2

Secchi Disk (m) 0.55 0.55 0.85 0.55 0.55 0.25 0.35 0.55 0.65

Air Temperature (OC) 26.0 29.0 19.0 12.0 0.0 11.0 23.0 28.0 25.0

9-3

Table 9-1 (cont.)

SAMPIT RIVER

Cruise No. 1 3 5 7 9 11 13 15 17

Month AUG SEP NOV DEC FEB MAR APR JUN JUL

Water Temperature (0C)
Surface 31.3 28.7 16.8 10.1 7.0 13.7 18.0 27.3 30.3
Bottom 32.8 28.3 17.2 12.4 7.0 13.4 28.3 27.1 29.6

Salinity (o/oo)
Surface 7.3 12.1 10.8 9.1 7.8 2.2 6.5 4.4 7.5
Bottom 17.3 13.9 11.3 10.9 7.8 9.8 6.5 7.6 7.8

Secchi Disk (m) 0.65 0.55 0.45 0.45 0.35 0.35 0.45 0.35 0.45

Air Temperature (�C) 25.5 28.0 20.0 21.0 0.0 13.0 25.0 28.0 31.0

PEE DEE RIVER

Water Temperature (oC)
Surface 29.0 28.6 16.7 10.5 7.0 13.7 22.0 27.9 30.1
Bottom 29.7 28.6 16.5 10.5 6.8 13.8 22.3 27.3 29.7

Salinity (o/oo)
Surface 10.0 10.0 7.9 4.7 5.2 2.9 3.7 3.8 4.8
Bottom 10.5 10.4 7.2 4.7 5.3 3.3 4.8 5.6 5.3

Secchi Disk (m) 0.45 0.45 0.45 0.35 0.35 0.35 0.45 0.45 0.45

Air Temperature (OC) 25.0 28.0 20.0 19.0 2.0 14.0 25.0 28.0 31.0

WACCAMAW RIVER

Water Temperature (oC)
Surface 30.0 28.4 16.7 10.2 7.0 13.9 25.9 28.1 30.3
Bottom 29.5 28.2 16.8 10.1 6.8 13.7 25.9 27.2 29.4

Salinity (o/oo)
Surface 5.3 5.0 3.2 0.5 0.4 0.5 3.4 2.5 0.0
Bottom 7.1 6.6 7.8 2.8 0.9 1.0 3.9 5.8 3.4

Secchi Disk (m) 0.45 0.45 0.75 0.35 0.35 0.25 0.35 0.45 0.35

Air Temperature (�C) 24.0 27.0 19.0 16.0 2.0 16.0 25.0 30.0 31.0

9-4

0.85 m (Table 9-1). Secchi disk readings were highly variable between

stations and no definitive seasonal trends were established. Air temper-

atures (Table 9-1) reflected water temperature patterns with lowest val-

ues recorded in February (0 to 2.OOC) and highest values in July or Sept-

ember (29.0 to 31.OOC).

B. ZOOPLANKTON

As with the physical and chemical data, zooplankton collections

from the six Winyah Bay stations can be divided into two groups: the

lower bay stations (Mother Norton, Mud Bay and Esterville Plantation),

the upper bay stations (Waccamaw River, Pee Dee River, Sampit River).

Throughout the year, the lower bay stations were consistently more di-

verse (8-25 categories, mean �S.D.:18�5.9; Table 9-2) than upper bay

stations (7-20 categories, mean �S.D.:10.2t3.7; Table 9-2). Densities

of zooplankton were also consistently greater at the lower hay stations

(Table 9-3), although there were occasional exceptions (i.e., Pee Dee,

March 1981; Sampit River, July 1981; Table 9-3) due to extreme abundance

of a single category. Of all stations, Waccamaw River was usually lowest

in abundance and diversity (ranked fifth or sixth of seven of nine times;

Table 9-3), followed by Pee Dee and Sampit Rivers. Overall, the lower

bay stations (MN, MB and EP) had the greatest densities of zooplankton

(12,000-13,000m3), NMF and SJ Creeks had densities of (8100/m3) similar

to those in North Inlet (9200/m3; Lonsdale and Coull, 1977) and the upper

bay densities were lowest (2000-6000/m3).

As in other locations on the southeast coast, numbers of zooplankton

were greatest in the warm months (April - September) and were reduced by

9-5

Table 9-2. Relative abundance of zooplankton on major cruises in Winyah Bay. Blanks indicat~ no organisms

were p. resent. A~breviations are: R: Rare (1 - 100/m~), C = Common (101 - 1000/m~), A: Abun-
oant ( > 1000/m ). PD: Pee Dee, WR = Waccamaw, SR = Sampit, EP = Esterville Plantation,
MB : Mud Bay, MN : Mother Norton.

8-15-80 9-26-80 11-7-80 12-19-80 2-3-81 3-6-81 4-24-81 6-5-81 7-15-81
PD WR SR EP MB MN PD WR SR EP MB MN PD WR SR EP MB MN PD WR BR EP MB MN PD WR SR EP MB MN PD WR SR EP MB MN PD WR SR �P MB MN PD WR SR EP MB MN PD WR SR EP MB MN
Copepods
Aoa~ti,~ tons~ A A C C A A A C A A A A C R C A A A R C A C A R C C C R R C R C C R A A A A A A A A A A A C A A C A
Acartia copepodids A C C C C C A C A A A A C C C A A A C A C A R R R R R C R R C R A A A A A A A A A C C C A C
C C
Oentropages homat~s R R R A A R A R A
~t~or~ ~ff~.i~ C R 6 C A C A R A R R C C R R
tabidoeera aestiva R R R R
ParuocaZan~s cz~ssizostlis C R A R R R A A A R C A A C C A R R R C C C C R C A R A C B R R C A
?s~udod~ptrm~s ooro~tus R C C R B R R C C R R C C R R R R C R R R C C R C C A R R R R
To~tanua setacaudatus R
?~lol.a t~blnata R R C C R B
Co~ycaeus sp. R R R R R
Oithona ooloa~va R R C R R R C C A R R C A B R C B R R R R C R C C R R C R R R R R R A
SaphireZla sp. R C R C R C B R R R C R R
Onc~ea venusta C R R R R
R
~terpin~ ac~tifrons R R C C C R C C R R R R R C R R R
Other harpacticoids R R R R R R R R R R R C R R R B R R R R R R C R R R R
I Copepod nauplii R R R R R C C C C C A A C R C A A R R R A C C C C R C C C C C C C C C R C C C C C C R R C R C R R R R C
Copepodiris R R R C R C C R C C C C A A A A A C A R R C R R R
Meropl ankton
Coelenterate larvae C R R R R R R R R R B C R R R R R C C R R C C C R
Pilidium larvae(Nemertea) R R R
Cyphonautes larvae(Bryozoans) R R R R R R R R R C R B
Trochophore larvae R R R R C R R C C R
Polychaete larvae R R R C C C C C C C C R R R C C R C R C R R R C C 6 R R R R R A R R C 6 R 6 R R R R C
Gastropod veligers C R R C C R C R C R R R C R R R R R R A C C R C R A C A R R
Bivalve larvae R R C R C R R C C C C R C R R R R R R R R
Barnacle nauplii C A C C R A R C A A C C A A A C C R A C C C R C C C A R R C A A A R A A C 6 C C A C A C C C A C C C
Barnacle cyprids R R R C R R R R R R C R R R R R C A R A A A A A C A C C R C R
Crab zoeae (other) C R R C C R R R C R C C C R C C A A C A R C C
Crab megalopae R R R R R
Shrimp larvae (other) R R R R
Decapod larvae (other) R R R R R R
Echinoderm larvae (starfish,
sea cucumber) C C R R R
Fish larvae R R B
Others
Hydroid polyps R R R R R R
Cladocerans R A R R R R R R R R
Ostracods R B R
Mysids R B R R R R R R C R
Cumaceans R R
Gamma rid amphipods R R R R R
Isopods R R R R R R R R R R R R R
Lucifer R
Chaetognaths C R R C R C R R R R R R R C
Appendicularians R R C C A R C A R R R C
Others R R R C R R R R R R R R R R C C R R R C R R R R R R R R C C R R

!
~ mini I~m ~ ~ ~ ~ ~i ~ ~ ~ ~ ~ m m ~ m i

Table 9-3. Abundance of common spp. in Winyah Bay, SC (#/m3). For station designation, see pages 1-10 and 1-13.

Species Station AUG SEP NOV DEC FEB MAR APR JUN JUL
Acartia tonsa PD 3657 5611 945 53 - 10 492 9967 3327
WR 1622 337 30 - - - 97 1958 330
SR 506 4071 505 174 19 68 1493 4198 3332
EP 452 4909 3785 6678 289 113 33023 3847 2279
MB 1646 10087 3998 454 109 56 14189 15399 699
MN 1037 7574 192 1335 216 128 6282 3816 1066

Acartia copepodids PD 1341 4497 159 8 - - 164 1554 646
WR 403 197 158 - - - 48 594 150
SR 194 2175 341 288 10 46 1050 2591 1563
EP 537 2108 1071 5427 72 103 5907 2276 351
MB 722 2934 4146 338 40 22 4300 8178 267
MN 624 4951 202 390 69 58 1384 778 200

Centropages hamatus PD
WR - - - -
SR - - -
EP - - - - 24 1889 -
MB - - - - 10 56 33
MN - - - 41 364 1649 2070

Table 9-3. Cont.

Species Station AUG SEP NOV DEC FEB MAR APR JUN JUL
Labidocera aestiva PD - - - - - - - - -
WR - _
SR -
EP - _ _ -
MB 9 - - - 12 -
MN 20 - - 30 - - - - -

Parvocalanus crassirostris PD - 39 46 - - - - - 9
WR - - - 10 - - - -
SR - 22 - - - - - - 16
EP 350 4266 322 326 96 123 100 49 26
M B 97 1551 139 239 99 201 342 1062 148
MN 6373 8665 1689 1170 303 790 4413 902 3475

Pseudodiaptomus coronatus PD - 49 34 - - - - - 4
WR - - -
SR - 33 35 7 10 - - 11 114
EP 85 404 125 49 24 - 25 173 -
MB 167 542 231 8 - - 265 861 28
MN 544 575 20 124 - 237 1284 48

Table 9-3. Cont.

Species Station AUG SEP NOV DEC FEB MAR APR JUN JUL

Oithona colcarva PD - 10 11 - 19 - - - 14
WR - - - 10 - - - -
SR - 22 - - 19 - - - 18
EP 60 644 62 16 40 41 13 - 11
MB 18 333 28 41 40 123 55 12 68
MN 725 2520 384 118 52 116 213 12 908

Euterpina acutifrons PD - - - - - - - - -
WR - - - - - -
SR - - - - -
EP 17 379 10 16 - 10 - -
MB - 283 120 - - - 22 - 8
MN 50 575 233 47 26 23 166 25 56

Gastropod veligers PD 106 733 - - - - - 3450 2069
WR - 9 - - - - 165 124
SR - 156 47 - - - - 412 2714
EP 43 13 21 - - - 13 12
MB 62 158 37 - - 22 33 1015 22
MN 131 59 30 - 9 12 95 99 45

Table 9-3. Cont.

Species Station AUG SEP NOV DEC FEB MAR APR JUN JUL

Bivalve larvae PD 10 68 - - - - - 10 4
WR 60 28 - - - - - -
SR - - - - -
EP - - - 16 8 - - -
MB 35 100 9 - 20 - - 35 33
MN 211 162 121 113 17 - 71 99 43

Barnacle nauplii PD 347 3226 307 107 37 39 29 182 816
WR - 47 - 8 - 10 - 99 90
SR 1984 2275 1810 1063 400 251 3366 1766 2996
EP 537 1300 3306 619 625 1673 1066 816 164
MB 651 1285 2971 239 725 2022 948 2466 482
MN 30 368 1143 177 441 1208 461 161 179

Barnacle cyprids PD 68 166 - 15 - - 10 3440 1147
WR 10 - - - - - 12 1089 341
SR 49 56 - 13 - 23 - 2707 923
EP - - - 49 8 - 288 1237 11
MB 18 33 74 - - 11 1069 1711 122
MN - - 30 130 26 - 59 148 15

m - _ m _

Tabl e 9-3. Cant.

Species Station AUG SEP NOV DEC FEB MAR APR JUN JUL

Crab zoea PD 289 - -8 --- 857 2111
WR 20 20 ---- - 495 557
SR 88 - - - - - - 63 2992
EP 665 50 - - - - - 235 45
MB 229 25 - - - - - 366 521
MN 81 118 - - - - - 1087 356

Crab megalopae PD - - - - - - - - -
WR - - - - - - ---
SR - - - - - - - 11-
EP - - - - - - - -
MB 9 - - - - - - 35 -
MN - - - - - - - 49 10

Chaetognaths PD - - - - - - - - -
WR - - - - - - - - -
SR - - - - - - - -
EP - 63 - - - - - - -
MB - 17 - - - - - 24 14
MN 242 103 20 6 - 12 12 99 151

Table 9-3. Cont.

Species Station AUG SEP NOV DEC FEB MAR APR JUN JUL

Appendicularians PD - 29 - - - - - - -
WR - 9 - - - - - - -
SR - - - . .
EP - 316 10 - - - - - -
MB - 158 - - - - - 47 2
MN - 1002 152 35 - - - 12 166

4- Total Zooplankton PD 5982 15386 1934 703 1073 12092 882 19722 9726
WR 5318 1038 248 828 1980 2238 1894 4730 2792
SR 3054 9078 2891 1712 792 4991 6187 12236 14317
EP 2858 15450 8836 17182 2108 7103 41050 9065 3291
MB 3883 19081 13511 1492 2306 4010 21675 32334 3676
MN 11094 29842 4862 5118 6873 7482 21528 9509 9233

as much as an order of magnitude in the winter (November - March). Den-

sities of meroplankton in particular decreased in the winter months, except

for barnacle nauplii and polychaete larvae (Table 9-2). The exception-

ally high density in the Pee Dee in March (Table 9-3) was due to one

Species, Eurytemora affinis (Table 9-2), which is characteristic of fresh-

er or less brackish waters. Eurytemora peaked in the upper bay between

March and July 1981, but was not found there, or was infrequent, between

August and December 1980. Species which appeared in the winter in North

Inlet and NMF or SJ Creeks, such as Centropages hamatus, never occurred in

the upper bay stations, so winter diversities were especially low there

(Table 9-2). In fact, C. hamatus was only abundant at Mother Norton

(Table 9-3), although it is a distinct and important winter component of

North Inlet (Lonsdale and Coull, 1977).

Lower and upper bay stations differ in the number of dominant species

as well as in diversity and abundance. In the lower bay, there are usually

more abundant species (Table 9-2), and several are copepods. In the upper

bay, rarely more than four species are ever abundant, and only 1-2 of these

are copepods. Dominant species in the lower bay are usually similar to

dominants in NMF and SJ, including forms such as Acartia tonsa, Parvocalanus

crassirostris, Pseudocalanus coronatus, Oithona colZcarva, and Euterpina

acutifrons. In the upper bay, however, there are some forms (particularly

Eurytemora affinis and several cladocerans) which do not occur, or are

rare in the lower bay.

Clearly, different species have very different distributions and are

abundant at different times. Only Acartia tonsa and barnacle nauplii are

relatively common at all stations during most times of the year. Many

forms, especially meroplankton, are more or less restricted to the lower

9-13

bay stations, and these are usually most abundant at Mother Norton (i.e.,

chaetognaths, Euterpina acutifrons, crab megalopae, bivalve larvae,

appendicularians; Tables 9-2, 9-3). Most of these species also occur

only in the warmer months of the year. Categories of larvae which occur

Year-round (e.g. barnacle nauplii, Table 9-3; polychaete larvae, Table

9-2) probably consist of several species with different spawning periods,

but no attempt was made to differentiate between species. At times, one

category will suddenly become dominant at a single station (e.g. crab zoeae,

Pee Dee and Sampit Rivers, July 1981; gastropod veligers, Pee Dee River

June-July, 1981; Table 9-3). Such occurrences represent samples which,

were taken at or near the time of peak spawning of one species. In the

case of the crab zoeae, the species was the brackish-water xanthid crab,

Rithropanopeus harrisi, which is not common in North Inlet, NMF or SJ

Creeks, or the lower bay.

In summary, zooplankton concentrations and constituents vary consid-

erably throughout the bay, both temporally and spatially. Winyah Bay is

an extremely complex system, and considerably more sampling must be perfor-

med to elucidate the patterns of abundance and distribution of zooplankton.

Winyah Bay sampling has been expanded in the second year of this study, and

a more complete description of zooplankton in Winyah Bay will beforthcoming.

For the present, the upper bay is obviously different, with fewer and dif-

ferent species present in generally lower numbers. Relatively few species

occur in both upper and lower bay stations, and the lower bay closely re-

sembles nearshore coastal and North Inlet environments. Seasonal changes

occur throughout the bay, but patterns are not always the same at all

locations. The implication of this temporal and spatial variability rela-

9-14

tive to human activities is that single perturbations which spread through-

out the bay may have very different effects on different portions of the

waterbody. This makes prediction of potential impacts of human activities

particularly difficult unless a considerable body of knowledge exists about

the environment.

C. EPIBENTHOS

Mysids or opossum shrimps, were the dominant organisms in sled collec-

tions on most cruises at most stations (Table 9-4). Neonysis americana

was by far the most common mysid in all collections, but low numbers of at

least five other species occurred at Mother Norton in August and September.

In August, mysid densities were high (40/m3) at Mother Norton, but low

(2/A3) at all other stations; in September, however, densities in the lower

bay decreased, and increased at all other stations, reaching over 60/m3 in

the Waccamaw River.

Mysids were generally more abundant in November (Table 9-5) when they

ranged from 79/m3 (Mud Bay) to 4/m3 (Sampit River). In December, mysid

densities decreased to the annual low (Table 9 -5). Densities remained

below 15/m3 at all stations in February and March. The mean density for

all stations on the April cruise was the highest since November (Table 9-5).

June densities were the highest of the year at most stations. At this time,

mysids were most abundant at the Pee Dee and Waccamaw River sites. July

densities were significantly lower (Table 9-5).

In summary, mysids were most abundant in fall and early summer, and

least abundant in winter and late summer. This pattern differs from that

observed in No Man's Friend and South Jones Creeks, where maximum abundance

9-15

TABLE 9-4. Dominant organism at each station on each cruise. Station
abbreviations are: MN = Mother Norton, MB = Mud Bay,
EP = Esterville Plantation, PD = Pee Dee, SR = Sampit River,
WR = Waccamaw River, ALL indicates the dominant for the
cruise based on mean density for all stations. Organism
abbreviations are CH = Chaetognath, MY = Mysid, FL = fish
larvae, SL = shrimp larvae, CM = crab megalopae.

MONTH MN MB EP PD SR WR ALL

AUG CH MY MY FL MY CH CH

SEP CH CH CH MY MY MY MY

NOV CH MY MY MY MY MY MY

DEC CH MY MY MY MY FL MY

FEB MY MY MY MY MY FL MY

MAR CH CH MY MY MY FL MY

APR CH MY MY MY MY MY MY

JUN MY CM MY MY MY MY MY

JUL CH CH MY SL MY SL MY

9-16

Table 9-5. Mean number of mysids, amphipods, shrimp larvae, chaetognaths, fish larvae and total organisms
per cubic meter for the Winyah Bay cruises from August 1980 through July 1981. Each entry
constitutes a mean for 12 sled collections at 6 stations,

MONTH MYSIDS AMPHIPODS SHRo LARVo CHAET. FISH LARVo TOTAL

AUG 7.3 0�2 1o4 13.4 1.2 34.7

SEP 16.1 1.0 008 6�8 0.2 29.7

NOV 21.1 1.1 0.1 3.8 0ol 28.2

DEC 2.9 1.2 0 1.1o 0.2 5.5

FEB 5.1 108 0 0.3 0.5 7.9

MAR 4.6 44 0.1ol 0.3 0.7 10.3

APR 18.4 1.4 0.1 1.0 0.1 22.0

JUN 38.9 1.0 0.9 3.9 0.8 59.2

JUL 4.4 0.7 0o9 3.8 0.1 10.4

occurred in winter at both creeks. However, the Winyah Bay February

and March densities were equal to those at NMF (Table 9-5 and Fig. 6-2).

Although the data clearly indicate that mysids were the dominant motile

epibenthic organisms in Winyah Bay, further analysis of the relationships

between physical characteristics of the water column and the abundance

and population structure of Neounisis americana are necessary before the

spatial and temporal distributions of mysids can be discussed in more

detail. The sampling program for the second year of this study is de-

signed to provide more specific information on mysid distribution.

Gammarid amphipods were somewhat more abundant at all Winyah Bay

stations than at either NMF or SJ Creeks (Tables 9-5 and 6-2), and

were collected in almost every sled tow on all cruises. Mean densities

for all stations were less than 2/m3 from August through February,

(Table 9-5). River station densities (WR,PD, and SR) were higher than

lower bay stations (EP, MB, and MN) on most cruises. With the exception

of the Waccamaw River collections, which yielded the largest catches of

amphipods in the study (20/m3), March densities were similar to previous

months. Gammarid densities from April through July were less than 4/m3,

and the means for all stations were comparable to those on the other

cruises.

Caprellid amphipods occurred in very low numbers on all cruises.

They were most common at stations closest to the ocean. No caprellids

were collected in the majority of the sled tows.

Since it was not possible to identify all amphipods collected to

species, and since the sled is not a very effective device for collecting

organisms which are so strongly associated with the bottom, these results

9-18

should be regarded only as preliminary assessments of the distribution

of these important organisms. High densities of gammarids probably

occur in shallow habitats throughout Winyah Bay where they constitute

major sources of food for juvenile fishes.

Cumaceans were collected in low numbers on all cruises and were

most commonly taken near the ocean. Densities were lower than those

of NMF and SJ Creeks during most of the year. Highest densities of

the year were observed in November at most stations. On this cruise,

the Mud Bay collections yielded over 4/m3. Sled catches probably

underestimate the actual abundance of these common benthic crustaceans.

Isopods, especially Aegathoa oculata, were more common in Winyah

Bay than in NMF and SJ Creeks. Highest densities consistently occurred

at the high salinity end of the estuary. Mother Norton tows yielded 10/m3

in September and 2/m3 in November. Otherwise, densities at all stations

were less than 2/m3. A few isopods were collected at Mother Norton in

December, but none occurred at the other stations on this cruise.

Decapod shrimp larvae and juveniles were collected from March through

November, but the densities for all stations were highest from June

through September (Table 9-5). Mother Norton catches were the larqest on

all cruises except July. Densities were generally less than 1/mn3, but

annual maxima of more than 3/m3 were recorded at Mother Norton and Wacca-

maw River in August. On this cruise, penaeid shrimp larvae dominated

the river collections. Mean densities for all stations were somewhat less

than those for NMF and SJ Creeks (Fig. 6-4). Palaemonid shrimp larvae

dominated the collection at the Pee Dee and Waccamaw River sites in July

(Table 9-4).

9-19

The seasonal pattern of abundance of the two sergestid shrimps,

Acetes americanus and Lucifer faxoni, was similar to that observed at NMF

and SJ. Both species were most abundant at the lower bay stations. The

density of Acetes and Lucifer at Mother Norton in August was 31/m3 and

24/m3, respectively. Densities were less than 4/m3 for all stations on

the other cruises. Only a few of each species were taken in December

and none were collected in February and March.

Crab megalopae were most abundant from June through September. Max-

imum densities were recorded in June at Mud Bay (51/m3) and Mother Norton

(14/m3). During July, densities were less than 2/m3 at all stations, but

crab megalopae were the dominant organisms in the sled collections at Mud

Bay in June and July (Table 9-4). In August and September, Mother Norton

densities were higher than all other stations. Lower bay collections con-

tained a variety of species of megalopae, while the river collections

were comprised chiefly of fiddler crab (Uca spp.) megalopae, Generally,

the seasonal pattern of abundance for all megalopae at the Winyah Bay

stations was similar to that at NMF and SJ Creeks, where June peaks were

also recorded.

Chaetognaths or arrow worms often dominated the sled catches at the

lower bay stations (Table 9-4). Maximum densities usually occurred near

the ocean, especially at Mother Norton. The mean for all stations de-

creased from an annual high in August to the annual low in February and

March, then increased in June and July (Table 9-5). Few chaetognaths

were collected in the upper bay from December through March.

Fish larval densities were generally lower at the Winyah Bay statior3

than at NMF and SJ Creeks (Table 9-5 and Fig. 6-9). Some larvae were

9-20

I ~~taken every month, but densities were highest in August, March and June.
In August, Mother Norton catches (6/rn3) included sciaenids, anchovies,

and gobies. September collections in the lower bay were smaller, but

the same families were represented. In November and December, croaker

I ~~larvae were collected at most stations. Young-of-the-year spot, summer

and southern flounder, speckled worm and American eel, and pinfish larvae

occurred at most stations. In addition to these species, March samples

contained pipefish and clupeid (herring) larvae. Clupeids were more

common in the river collections. April collections were characterized

I ~~by lower numbers of large croaker, spot and pinfish larvae. In June,

fish larval diversity increased considerably. Whiting, silver perch,

star drum, hogchoker, goby, blenny and anchovy larvae were collected

throughout the estuary. No major changes in composition were recorded in

July, although densities were much lower than in June (Table 9-5).

Several factors are probably responsible for the relatively low

densities of fish larvae collected at the Winyah Bay stations. One

factor is related to the duration or longevity of early life stages.

I ~~~The developmental time from egg to postlarva is on the order of weeks

for most estuarine fishes, and even though larvae representing most of

species were collected with the sled, species with short spawning and

fl ~~developmental times were probably missed during the six week interval

between cruises. Another factor is station location. Fish larvae are

I ~~~more common in shallow water than in the relatively deep channels and

3 ~~~open waterways where the first year stations were located. Also, avoid-

ance of the collection apparatus by fish larvae most likely contributed

3 ~~~to the low numbers in the collections. In summary, low densities of

larvae determined in this study are probably the result of under-

9-21

sampling, rather than to low numbers of larval fishes in the estuary.

A more detailed analysis of the spatial and temporal distribution
of major fish species will be conducted after the second year sledI

study in Winyah Bay is complete. Preliminary analyses indicate that

certain stages (sizes) of many species occur in different sections of

the estuary (ocean to river) as they develop. For instance, spot larvae3

appeared to be much more abundant in the creeks than in the Winyah Bay

channel stations, while croaker seemed to be more common at the bay andI

river stations than either NMF or SJ Creeks.

In summary, organisms were most abundant in the lower bay during

the warmest months. The diversity of organisms was also greater nearestI

the ocean. Fifteen of the seventeen categories of animals identified in3

sled samples at NMF and SJ Creeks were collected at Mother Norton Shoal

in the lower bay, but only eight of these categories were represented

at the Waccamaw and Pee Dee River sites. Mysid shrimps were the most

abundant motile epibenthic organisms at all stations (Table 9-4).I

The diversity of organisms at all stations was greater between3

April and November than during the winter. The seasonal patterns of

abundance for all species in Winyah Bay, with the notable exception ofI

mysids, were consistent with trends at NMF and SJ. Densities of total

organisms in sled collections at NMF, SJ and Winyah Bay were greatest in

June (Fig. 6-10 and Table '9-5).1

A great deal of variability in the spatial and temporal distribution*

of motile epibenthic organisms was apparent from the analysis of the first

year's collections. Much more study of the ecology of early life stag~esI

9-22

of shrimps, crabs, and fishes in Winyah Bay are necessary before the
B ~~~impacts of petroleum and other pollutants can be predicted accurately,
* ~~~but these data indicate that such impacts could have immediate and
long-term effects on estuarine populations.

I~~~~~~~~~~~~92

CHAPTER 10. IMPACTS OF PETROLEUM ON ESTUARINE ECOSYSTEMS;
I ~~~~~~~~PROJECTIONS FOR WINYAH SAY'

Estuarine and coastal areas receive petroleum hydrocarbon inputs

from many sources, including natural seeps, offshore production (blow-

outs, ruptured lines, accidents, normal operational discharges),

I ~~~transportation losses (tanker accidents, dry docking, normal terminal

j ~~~operations, bilge cleaning, nontanker accidents), coastal refineries

(normal and accidental discharges), the atmosphere, coastal municipal

3 ~~~wastes and industrial wastes, urban and river runoff. Discharges into

the marine environment have been summarized in the National Academy of

S ~~~Sciences report on petroleum in the marine environment (NAS, 1975).

Crude oil contains many different components which vary accord-

5 ~~~ing to molecular size and type. Degradation processes for crude oil and

various chemically dispersed oils have been described in NAS (1975) and

I ~~~the Proceedings of the 1981 Oil Spill Conference (American Petroleum Inst.,

3 ~~~1981). Oil released to the aquatic environment immediately undergoes many

alterations. Initially spilled oils spread rapidly into thin layers,

I ~~~forming an oil slick. Hydrocarbons less than 15 Carbon molecules long
evaporate and are volatilized from the surface waters within 10 days

(Kreider, 1971). Othpr hydrocarbons are dissolved or form particles, many

of which settle into the sediments. Hydrocarbons also form tarballs, and

some are removed by photochemical oxidation. Petroleum products are also

3 ~~~subject to microbial degradation and uptake by organisms.

� ~~~~~~~~~~~~10-1

Impacts of hydrocarbons on estuarine organisms are influenced by

many factors, including amount of oil released, type of oil (crude oils

are generally less toxic than the refined fractions), solubility of

the oil, and reactions with dispersants. Dispersants used to treat oil

spills, or dispersant/oil combinations, may be more biologically damag-N

ing than the hydrocarbons which were initially released. Currents, cir-

culation, morphometry of the area, and meteorological conditions can

also affect toxicity. Highly turbulent zones such as sandy beaches are3

usually less sensitive to oil spills than estuaries and salt marshes

(Gundlach and Hayes, 1978). High current and wind velocities in theI

open sea during storm conditions may disperse oils more quickly, there-3

by reducing their impact. However, in enclosed areas, such conditions

may spread the oil over large, more sensitive areas (e.g., salt marsh

and estuarine communities). Turbulent factors also increase the sus-

pension of particulate materials to which oil adheres. Greater concen- '

trations of oil are carried to bottom sediments when turbidity is

greatest. Timing of the impact is also important because spills during

the warmer months of the year are more likely to affect sensitive larval3

stages and reproductively active adults.I

Several mechanisms have been described through which plants and3

animals are exposed to oil. Direct contact is the most obvious method

and is often responsible for decreased growth, fouling of feeding and3

swimming structures, or death. Hydrocarbons can be absorbed through the

body walls of many organisms. Other mechanisms include ingestion of oiled

particles and food chain transfer through ingestion of contaminated prey

items. Impacts vary depending on mode of contact, duration, exposure,

and type of oil or oil fraction. Effects may be categorized as being3

10-2

acute or chronic. Acute effects are generally immediate and severe, and

may include death or debilitation. Acute exposure to aromatics during

the first few days after an oil spill may be responsible for many of

the reported fish and bird kills, and population declines of plankton

and larvae. Chronic effects generally result from continued exposure to

refinery effluents, repeated small spills, or resuspension of contamin-

ated benthic sediments, and may be lethal or sublethal.

A complete review of all pertinent literature was not feasible

in this study, but we have cited many excellent articles and reviews

which describe case histories of actual oil spills (e.g., American Pet-

roleum Institute, 1981; NAS, 1975). We wish to summarize the abundant

literature, particularly emphasizing acute and chronic effects of pet-

roleum upon groups of organisms which are likely to be most severely

affected in Winyah Bay. A review of potential effects by group is followed

by predictions of potential impacts on Winyah Bay, based on current know-

ledge and information obtained in this study regarding the bay and

important exchange areas.

Phytoplankton and Macrophtes

The effects of petroleum hydrocarbons on phytoplankton have been

previously reviewed (Corner, 1978; Johnson, 1977; Snow, undated; Van-

dermeulen and Ahern, 1976). Effects vary depending on the sensitivity

of the species and the concentration of oil to which they are exposed

(Dunstan et al., 1975; Mironov, 1968, 1972; Mironov and Lanskaya, 1966;

Pulich et al., 1974; Thomas et al., 1980). Species sensitivity is gov-

erned by many factors, especially physiological condition (Stoll and

10-3

Guillard, 1974). The severity of an oil spill also varies seasonally

and is generally greater during spring or summer months (Gordon and

Prouse, 1972; Fontaine et al., 1975). Other factors, including water

solubility (Currier, 1951; Kauss et al., 1973) and reactions with dis-

persants affect hydrocarbon toxicity (Batelle, 1973; Scott et al., 1979).

Heavy concentrations of crude oil have long been known to inhib-

it phytoplankton growth (Galtsoff et al., 1935). More recent laboratory

studies have adequately demonstrated the detrimental effects of petrol-

eum hydrocarbons on both marine phytoplankton (Mironov and Lanskaya,

1969; Mommaerts-Billet, 1973; Pulich et al., 1974) and freshwater species

(Kauss and Hutchinson, 1975; Soho et al., 1975a,b). Extensive damages

following actual oil spills have also been described (Diaz-Piferrer,

1962; Clark et al., 1973).

Specific effects of oil exposure include inhibition of cell div-

ision and subsequent reductions in cell number (Mironov and Lanskaya,

1966), inhibition of photosynthesis (Gordon and Prouse, 1972), reduct-

ion of CO2 exchange (Shiels et al., 1973), damage to the plasma membrane

(Van Overbeck and Blondeau, 1954), inhibition of oxidative phosphoryl-

ation (Vandermeulen and Ahern, 1976), modification of DNA and RNA pol-

ymerization (Davavin et al., 1975) and elimination of bicarbonate up-

take (Kauss et al., 1973).

Low concentrations of oil stimulate growth and photosynthesis in

some species (Snow and Scott, 1975; Shiels et al., 1973). Some hydrocar-

bon fractions inhibit photosynthesis at all concentrations (Parsons et

al., 1976) and phytoplankton populations may never recover after

10-4

initial exposure to hydrocarbons (Lee et al., 1977). Generally, the

lag phase in population growth is lengthened and the exponential phase

is depressed. Recovery of phytoplankton populations after initial in-

hibition has been related to large evaporative losses of hydrocarbons

(Vandermeulen and Ahern, 1976; Lacaze, 1974; Mahoney and Haskin, 1980).

The effects of oil on macrophytes has been reviewed by Johnson

(1977) and Snow (Undated). Several studies have examined the impacts

of acute oil spills on marshes (Stebbings, 1968; Burns and Teal, 1971;

Lytle, 1975; Macko et al., 1981; Bender et al., 1977; Hershner and Moore,

1977) and prolonged exposure to refinery effluents (Baker, 1976a,b;

Dicks, 1976). Results generally indicate that marsh grasses can survive

a single mild exposure to oil, but multiple doses may be fatal.

Responses of macrophytes to hydrocarbon exposure are varied. Ef-

fects may be severe, and large macrophyte communities may virtually

disappear (Ranwell, 1968; Anonymous, 1953). Reported increases in phyto-

plankton and macrophyte populations after exposure may be due largely

to the decimation of herbivore populations (North et al., 1965; Miller

et al., 1978; Johansson et al., 1980). Seed germination may be almost

completely inhibited after exposure to crude oil (Baker, 1971). Stands

of Spartina alterniflora exposed to multiple doses of oil experience

serious lethal effects and many sublethal effects, including delayed

development, increased density, reduced mean weight per stem, and sup-

pression of cohort production (Hershner and Lake, 1980).

Zooplankton

Contact with hydrocarbons can result in a variety of effects in

zooplankton which differ from species to species. Some forms may simply

rid themselves of the hydrocarbons (deputation) with relatively little

negative effect; others may metabolize it to less toxic forms and store

it in lipids or other compounds (Sanborn and Malins, 1977), whence it

can be passed up the food chain; in other instances sublethal effects

such as reduced offspring number or lifespan can be induced; finally,

contact with hydrocarbons or dispersants can have direct lethal effects.

Numerous studies (e.g., Wells, undated; NAS, 1975) have documented

direct death in zooplankton populations from contact with hydrocarbons,

both in the field and in the laboratory. On the other hand, Conover

(1971) found relatively little effect of oil on copepods, and showed

that ingestion of oil could result in transport of up to 20% of the oil

from the surface to the bottom in the form of fecal pellets. Other studies

have shown that zooplankton ingest oil in particles of various sizes

(Wells, undated), that feeding rates or particle selection can be mod-

ified by the presence of various sizes of oil particles (Berman and

Heinle, 1980), and that rate of deputation of oil may depend upon whether

it was ingested (slower) or taken up through the body wall (faster;

Corner et al., 1976). The effect in any given survey or experiment dep-

ends on types of oil Or oil fraction, concentration, time of exposure,

environmental conditions (temperature, salinity, etc.) and species of

zooplankton.

10-6

Sublethal effects are the most difficult to document, and are

often hard to recognize. In addition, the impact of various sublethal

effects on zooplankton populations is difficult to predict because of

the lack of understanding of zooplankton biology in general. Documented

sublethal effects of exposure to oil include changes in rates of feed-

ing, reduction of activity levels (e.g., immobilization or narcotization),

behavioral changes (e.g., loss of orientation, loss of ability to sel-

ect substrates, loss of sensory abilities), physiological effects (e.g.,

reduced respiration/excretion rates), and life history effects (e.g.,

reduced clutch size, clutches per lifetime, offspring viability, or

adult life span). The variety of sublethal effects on zooplankton are

reviewed in Wells (Undated).

Studies performed on zooplankton (usually in boreal or temperate

waters) have shown that most zooplankton as individuals are very sen-

sitive to dispersed and dissolved petroleum (NAS, 1975; Wells, undated).

This sensitivity must be considered in light of the great diversity of

zooplankton and the variety of oil types and fractions they might contact.

Considerable work has been performed on some groups, especially proto-

zoans, coelenterates, ctenophores, polychaetes, molluscs, crustaceans

(especially barnacles, copepods, amphipods, mysids, shrimps and crabs),

echinoderms, and fishes. Other groups largely have been ignored, such as

foraminiferans and radiolarians, cladocerans, ostracods, cumaceans, iso-

pods, larvaceans (appendicularians), and chaetognaths. In most cases,

the groups mentioned above have not been studied in the southeastern

United States, except for the Gulf coast of Louisiana and Texas. Al-

though results vary, some forms (i.e., ctenophores and decapod larvae)

appear to be particularly sensitive to hydrocarbons. Decapod larvae are

10-7

more susceptible during molting, or in the early stages of development.

some studies have shown that barnacle larvae are fairly sensitive (Wells,

undated), but others (e.g., Lee and Nicol, 1977) have shown that they

are more resistant than most copepods. Sensitivity of molluscs and ech-

inoderms varies, but early cleavage stages are usually more sensitive

than eggs or adults (Wells, undated).

Few toxicity studies have been performed on species which are

found in the study area; in a recent review of the literature on zoo-

plankton from Cape Hatteras to Cape Canaveral, Alden (1977) cited no

studies of oil effects on southeastern plankton. Lee and Nicol (1977)

studied effects of No. 2 crude oil on coastal/oceanic zooplankton in

the Gulf of Mexico, and concluded that although coastal zooplankton

were more tolerant of the water-soluble fractions (WSF) than the oceanic

forms, they still suffered negative effects ranging from reduced survival

to behavioral aberrations. They attributed differences between coastal

and oceanic zooplankton to the fact that there were larger numbers of

particularly resistant forms (barnacle nauplii, polychaete larvae) in

the coastal plankton, and speculated that holoplanktonic forms were more

sensitive.

Studies of Eurytemora affinis(reviewed by Dawson, 1979), a species which

occurs in upper Winyah Bay, showed that ingestion rates were reduced by

38% in concentrations of oil which might be found under a spill (0.52

mg/1). Exposures to more than 1 mg/l resulted in narcotization and death.

Numerous life history effects were also recorded, including reduction

in adult life span, clutch size, and number of eggs/lifetime when E.

affinis were exposed to WSF or Naphthalene. Exposure to concentrations

10-8

of hydrocarbons for less than 4 hours (as under a spill) could have sig-

nificant negative sublethal effects on E. affinis life history parameters.

Numerous studies have been performed on species of Acartia, in-

cluding A. tonsa. Berman and Heinle (1980) found that concentrations

of fuel oil of 70 ug/l did not affect feeding, but concentrations of

250 ug/l resulted in several different types of feeding modifications,

from reduced feeding rate to changes in the sizes of particles filtered.

Hebert and Poulet (1980) reported that exposure to Venezuelan crude oil

rapidly and significantly reduced growth and survival of Acartia hudson-

ica, and that feeding behavior and particle size selection were also

~affected. Ott (1980) found that egg production was significantly de-

pressed by exposure to 50 ug/l napthalene, and that young females were

more sensitive than older females. In addition, a higher percentage of

infertile eggs were produced during early exposures to naphthalene.

Studies on locally-occurring crabs generally bear out the results

of investigations in other areas: early larval stages ave mote sensitive.

Laughlin, Young and Neff (1978), working with Rhithropanopeus harrisii

(a species which occurs in the fresher waters of Winyah Bay) found that

all larval stages were negatively affected by exposure to sublethal

concentrations of water-soluble fractions of No. 2 fuel oil. Earlier

stages were more sensitive, but later stages, including megalopae and

adults, appeared to recover from chronic sublethal exposure. The major

effect of chronic exposure on these crabs may be reduction in population

size or viability due to reduced recruitment into the adult population.

Cucci and Epifanio (1979) found negative effects in larvae of the mud

crab Eurypanopeus depressus when exposed to various concentrations of

10-9

WSF of Kuwait crude oil; as with previous investigators, they found

more effects in earlier stages, but also a greater incidence of morph-

ologically abnormal megalopae after exposure.

In summary, effects of exposure to various types and concentrations

of hydrocarbons appear to have similar impacts on southeastern zooplank-

ton as on plankton studied in other parts of the world. These may range

from immediate mortality to relatively innocuous and temporary behavioral

modifications. The degree of impact can vary considerably depending upon

exposure, species, life stage of the organism and environmental conditions.

Benthic and Intertidal Organisms

Many studies have shown that petroleum products cause a variety

of lethal and sublethal effects in marine and estuarine organisms, in-

cluding benthic or epibenthic forms (reviewed in NAS, 1975; Percy,

undated). One of the important variables governing the impact of oil

is habitat type; oil on a high energy coastline may be rapidly removed,

whereas if it impinges on low-energy environments, considerable time

may be required to disperse it. Gundlach and Hayes (1978) have dev-

eloped a vulnerability index which indicates that inter- and subtidal

habitats in estuaries like Winyah Bay/North Inlet are among the most

difficult to clean, and once inundated with oil, take the longest time

to return to normal conditions (Sanders et al., 1980). This is largely

because estuarine inter- and subtidal habitats contain fine, porous

mud-sand substrates which readily incorporate and retain oils under the

low-energy hydrographic regime in which they occur.

10-10

Intertidal organisms are especially susceptible to physical

damage (coating, smothering, fouling) by oil because of their ex-

posed position (Straughan, 1972). Fine particulate material is coated

with oil and incorporated into inter- and subtidal sediments, from which

toxic hydrocarbon fractions can leach for long periods of time. Many

authors believe that intertidal organisms are actually less susceptible

to oil inundation than subtidal animals because of their inherent resis-

tance to physical stresses (Newell, 1970), but direct negative effects

(e.g., reduced growth or metabilism, behavioral aberrations, mortality)

from spills have been demonstrated for most benthic taxa (George, 1970;

Rossi and Anderson, 1978; Thomas, 1978) both inter- and subtidally.

Most benthic organisms rapidly take up hydrocarbon fractions, which

cause various physiological, behavioral, and metabolic effects; many

of these organisms quickly depurate hydrocarbons when put into clean

water (Lee, 1977). There is usually rapid uptake and loss to a stable

level in which some hydrocarbon fraction remains in the organisms in

a detoxified or metabolized form (e.g., Anderson, 1975). Such stored

hydrocarbons can be passed up the food chain, reaching even humans in

the case of commercially important species like oysters, clams, shrimps

and crabs.

Sublethal effects on benthic organisms are numerous, and include

reduced or increased respiration rates (Gilfillan, 1973; Percy, 1977),

formation of neoplastic lesions (Albeau Fernat and Laur, 1970; Yevich

and Barszcz, 1976), narcosis or reduced muscular activity (e.g., Corner

et al., 1976), and reduction of chemosensory ability (Atema et al., 1973;

Pearson and Olla, 1979). Modification of growth rate, molting ability

10-11

or frequency, and reproductive processes are especially important sub-

lethal effects which have major implications for populations of benthic

and intertidal invertebrates. The vast literature on these subjects re-

ports considerable differences in the degree to which exposure to pet-

roleum causes sublethal effects among taxa (Percy,undated), but nearly

all species studied to date are affected to some degree.

Larvae and juveniles of benthic organisms are more severely affected

by contact with petroleum than adults. Larvae of many commercially

important species (e.g., crabs, oysters, clams) as well as non-commercial

forms (e.g., polychaetes, barnacles) have been shown to be injured in

various ways by petroleum fractions (Caldwell et al., 1977; Byrne and

Calder, 1977), and death of larvae or of newly settled or hatched juveniles

(e.g. Edwards, 1980; Woodin et al., 1972) has frequently been recorded.

Although Tatem, Cox and Anderson (1978) found that young penaeid shrimp

were more resistant than older shrimp, the opposite is true for most

benthic invertebrates. One of the major effects of oil spills on benthic/

intertidal organisms is the reduction of population size or viability by

loss of recruits.

In summary, benthic and intertidal organisms suffer negative im-

pacts from acute exposure to hydrocarbons and from long-term chronic

exposure. Although the effects vary between species and habitats, they

are generally negative, and may lead to significant changes in the

quality of the ecosystem or the value of the resources which may be

taken from the system.

10-12

Fish

Impacts of oil spills on fish populations are variable, and range

from little or no effect to large fish kills (Gooding, 1968; Cerame-Vivas,

1968). In creeks receiving chronic discharges of oil field wastes, 5-16

times fewer gamefish were harvested and yields of blue crabs and forage

fish showed similar declines (Spears, 1971). These adverse impacts were

thought to extend into the bay which received the creek input. Petrol-

eum-based hydrocarbons are magnified in the food web (Lu and Metcalf,

1975; NAS, 1975; Koons et al., 1976), and therefore may pose a more ser-

ious hazard to higher trophic level organisms such as fish. Effects of

oil exposure depend upon many environmental conditions, including sal-

inity and temperature (Lind6n et al., 1979). Effects of chronic oil

exposure may be most severe to fish species which are year-round residents

and are frequently in contact with bottom sediments such as flounders

and eels (Fletcher et al., 1981), or feed on bottom organisms, such as

the endangered short-nosed sturgeon.

Primary stress responses include increases in osmolality, concent-

rations of plasma glucose (hyperglycemia) and cholesterol (Thomas et al.,

1980), and increased respiratory (or opercular) rates (Thomas and Rice,

1975; Brocksen and Bailey, 1973). Other possible effects include de-

creased growth rates (Hawkes, 1977; McCain et al., 1978), increased

liver to body weight ratios (Yarbrough et al., 1976), fin rot (Min-

chew and Yarbrough, 1977), severe damage to gill epithelial tissue (Nu-

wayhid and Davies, 1980; Clark, Finley and Gibson, 1974; Blanton and

Robinson, 1973), induction of benzo(a)pyrene monooxygenase activity

(Kurelec et al., 1977; Payne and Penrose, 1975; Payne, 1976), and hist-

ological damage to chemoreceptors (Gardner et al., 1973). Oil exposure

10-13

also may result in the tainting of fish flesh (Mackie et al., 1972;

Blumer, Souza and Sass, 1970; Shipton et al., 1970).

Fish larvae are very susceptible to oil pollution and treatment

with dispersants (Wilson, 1977), although species differ as to their

sensitivity (Kuhnold, 1970). Larval effects also include disruption of

phototactic and feeding behavior (Wilson, 1970). Fry show avoidance

reactions to hydrocarbons, which may disrupt migrations (Rice, 1973).

Fish embryos exposed to oil experienced decreased hatching, damage

to liver, kidney, lens and epithelial tissues, mitochondrial damage

(Ernst and Neff, 1977; Cameron and Smith, 1980), and decreased survival

(Linden, 1978). Bouyant fish eggs tend to congregate at the water sur-

face and are especially susceptible to the effects of toxins. Effects

of treatment with oil dispersants include abnormalities in cell division

and differentiation, reductions in heart rate, eye pigmentation, growth

rate, and hatching success (Wilson, 1976).

Birds

Of the groups of vertebrate animals that are exposed to oil pol-

lution, birds are probably the most adversely affected (see reviews

by NAS, 1975; Brown, undated). Diving birds in particular are severely

affected by oil spills. This group includes the familiar pelicans,

coots, cormorants, loons, grebes, mergansers, and the highly gregar-

ious diving ducks. For example, nearly half of the Tay estuary population

of diving sea ducks was lost in 1968 as a result of the Tank Duchess

oil spill (Greenwood and Keddie, 1968). The size of the oil spill usually

10-14

gives no indication of the magnitude of the damage. More than 5,500

birds were killed by the leakage of only about 27 tons of oil from the

barge Irving Whale along the coast of Newfoundland (Brown et al., 1973).

One of the most serious effects on birds is the breakdown of

feather structure, which results in loss of waterproofing and insulation

(Hartung, 1967). This condition leads to severe thermal stress and may

often result in the death of the afflicted bird.

Oil is ingested by birds through preening activity (Hartung, 1965)

and feeding on contaminated prey organisms. Ingested oil has been re-

ported to cause heterotrophy of the nasal gland, liver, adrenals, and

changes in the morphology of intestinal tissues in some birds (Miller

et al., 1978b). Other possible effects include physiological stress

(Butler et al., 1979; Crocker et al., 1974, 1975), inhibition of nutrient

transfer (Miller et al, 1978a,b) reduction of growth (Miller et al.,

1978a) and narcotization (Southward, 1978). Crude oil ingested by

female birds causes reproductive success to decline by decreasing egg

production, hatchability, and egg shell thickness

(Hartung, 1965; Holmes et al., 1978; Grau et al., 1977), and by reducing

survival of offspring produced by these birds (Vangilder and Peterle,

1980).

Oil may easily be transferred to the surface of eggs by oiled

parents during incubation. Experimentally applied oil resulted in the

death of embryos of mallards, eiders, herons, gulls and terns (Albers,

1977; Coon et al., 1979; Hartung, 1965; Szaro and Albers, 1977; White

et al., 1979).When female mallards were smeared with only 5 ml of

mineral oil, the eggs didn't hatch.

10-15

In summary, bird populations may be severely affected by oil spills.3

Adverse impacts are likely to be most serious in areas where birds are

highly concentrated, especially breeding and feeding grounds and in3

waters adjacent to major migratory flyways.I

Mammals3

Very little is known about the potential impacts of an oil spill3

on mammal s. Although the effect of oil on muskrats has been documented

(McEwan et al., 1974), most of the existing information regarding ef-

fects on mammals pertains to groups which occur outside of the study3

area, such as seals (refer to Geraci and Smith, 1976; Smiley, undated,

for lists of pertinent references).

Specific effects may include damage to appendages (Warner, 1969;3

Davis and Anderson, 1976), eye irritation (Geraci and Smith, 1977), re -

duction of insulating properties of fur (Kooyman et al., 1977) and the

formation of mild kidney lesions (Smith and Geraci, 1975).

Summary and Predictions for Winyah Bay

Potential acute and long-term effects of a large oil spill in salt

marsh and estuarine environments have been considered in this chapter,5

as well as effects of low-level chronic hydrocarbon inputs. Marine

organisms are exposed to hydrocarbons through four basic mechanisms:I

direct contact,uptake of dissolved fractions through the body wall, in-3

gestion of contaminated prey organisms, and direct ingestion of oil

or oil-laden particles. Hydrocarbons can cause acute (direct) or3
10-16

3 ~~~sublethal effects in organisms, which range from immediate death to

reduced growth and reproduction.

Toxicity of hydrocarbons may vary for a number of reasons. Dir-

I ~~~ect contact produces the most immediate and damaging effects, but

3 ~~~ingestion or uptake also cause lethal and sublethal damage. Impacts

vary according to the amount and types of oils involved, and highly

refined fractions are frequently most toxic. Dispersants and dispersant/

oil combinations sometimes result in more significant adverse impacts

I ~~~than the oil itself. Populations of highly sensitive species may be

3 ~~~totally destroyed, whereas other species may suffer less dramatic sub-

lethal effects, and species of low sensitivity may actually experience

3 ~~~sudden dramatic population increases (Sanders et al.,1980).

I ~~~~~Susceptibility of organisms varies with habit and stage of life

3 ~~~cycle. Heavily oiled marsh grasses, such as Spartina aZternifzora, will

die, and less-heavily contaminated grasses will experience sublethal

3 ~~~effects, including decreased growth and inhibition of seed germination.

Buoyant eggs and surface-dwelling organisms will be affected by direct

I ~~~contact, while animals and plants in the middle part of the water col-

5 ~~~umn will be most severely affected by the water-soluble fractions and

by contact with or ingestion of oiled particles. Benthic and intertidal

3 ~~~organisms will be affected by smothering, direct contact with or ingest-

ion of oiled sediments. Larger, more motile animals (fishes, shrimps,

I ~~~and crabs) may or may not be able to avoid direct contact, but will

still be affected by ingestion of hydrocarbon-containing organisms low-

er on the food chain or absorption of water-soluble fractions through

* ~~~their body walls.

10-17

Effects of oil on aquatic organisms often vary seasonally, and

are generally more severe during the warmer months when larval and

planktonic forms are abundant and when reproductive activity is high.

Many commercially important species may be affected, particularly in

the larval (decapods, shrimps, fish) or the newly-settled juvenileI

(clams, oysters) stages. Soft-bodied forms (e.g., ctenophores, jelly-

fish, and appendicularians) are poorly studied, but appear to be esp-

ecially sensitive to hydrocarbon pollution.3

Birds are abundant in highly productive estuarine systems and areI

probably the most severely affected vertebrate group; oil spills may3

result in almost total destruction of local populations. Spills ad-

jacent to breeding, feeding and rafting areas result in an unusually

high number of casualties and may severely affect population levels for

many years. Temporary visitors may also experience adverse effects,I

especially when oil spills occur in areas adjacent to major flyways�

of birds or migration routes of aquatic organisms (e.g., marine turtles,

anadromous and catadromous fishes).3

The most extensive long-term study of the effects of an oil spill3

in an' estuarine habitat (Sanders et al., 1980) showed that negative

impacts, such as instability in density, diversity and species rich-

ness; and physiological and behavioral disorders, persisted as long as5

seven years after the initial spill. There is no reason to believe that

similar habitats along the east coast of the United States would behave3

differently, or would be less affected by an oil spill.

10-185

Estuarine areas subject to chronic low-level hydrocarbon inputs,

such as those receiving refinery effluents, experience high mortalities

* ~~~of marsh grasses near the area and changes of species composition and

abundance of both flora and fauna. Areas near the effluent source suf-

I ~~~fer the most severe impacts, and pollutants accumulate over time, part-

3 ~~~icularly in systems with low circulation properties. Effects are less

likely to be acute, but sublethal effects may be widespread. Reduced

3 ~~~catches of commercially important species (fishes, and crabs) and

forage species are likely to occur in adjacent bays receiving the effluent.

I ~~~~~In a broad, relatively shallow estuary like Winyah Bay, one would

* ~~~expect an oil spill to spread rapidly throughout a large portion of

the bay, coming in direct contact with intertidal marshes, oyster bars

I ~~~and mudflats, all designated as highly sensitive areas (Gundlach and

Hayes, 1978). Because of the high amount of suspended particulates i~n

I ~~~the bay, there would be rapid incorporation of oiled particles into the

sediments, particularly in areas with high sedimentation rates such as

Mud Bay. Over several tidal cycles, oil would be carried into the near-

3 ~~~shore environment, impinging upon sandy beaches on North, South, Sand

and possibly even Cape Islands. Removal from these beaches would occur

I ~~~relatively rapidly (Gundlach and Hayes, 1978). However, severe impacts

on the nests of loggerhead turtles on these beaches would be expected

if the spill occurred during the nesting season. Nests which occur in-

5 ~~~side the bay on beaches (i.e., Cat Island) would also be affected. Oil

would probably be transported to adjacent aquatic systems including

I ~~~the Santee River and North Inlet via the intracoastal waterway and NMF

and SJ Creeks. All protected and natural habitats presently bordering

the bay would receive at least some direct oiling. These effects
5 ~~~would be exacerbated during times of high water movement, such as spring

10-19

tides, storms, or periods of high winds. Wind direction would play a

major role in determining which shores of the bay would be most heavily

oiled.

An oil spill would probably have severe negative impacts on most

of the flora and fauna which occur within the bay. The vast borders of

Spartina aZternif'Zora would be killed by direct contact, and plants

which survived would probably suffer long-term sublethal effects. Phyto-

plankton in the area of the spill would be killed, but subsequent

phytoplankton blooms would occur after most of the oil was incorporated

into the sediments or shoreline. Many of the native intertidal invert-

ebrates, particularly fiddler crabs, oysters, mussels, snails and barn-

acles would suffer direct mortality by contact with oil. Survivors

would be expected to experience sublethal effects, including behavioral

and physiological disorders, reduced growth and reduced or aberrant

reproduction for many years.Populations of intertidal invertebrates

would drop, and recover slowly, due to reduced recruitment by larvae

and juveniles, and subsequent death of recruits exposed to hydrocarbons

leaching from oiled sediments. Subtidal benthic and epibenthic organ-

isms, including polychaetes, clams, numerous small shrimps, mysids,

amphipods and fish larvae would be killed or damaged by direct contact

with oil or oiled sediments, or by ingestion of oiled organisms or

particles. Recruitment into muddy or muddy-sandy sediments would be

greatly reduced, and benthic communities might take years to recover

due to fundamental changes in sediment characteristics brought about

by the deaths of the structuring organisms living within the sediments.

Bottom-feeding organisms, including threatened or endangered species

like the shortnose sturgeon and loggerhead turtle, would suffer by loss

10-20

of their food sources and by ingestion of oiled organisms. So little

is known about these organisms that prediction of sublethal effects is

I ~~~impossible.

N ~~~~In the water column, zooplankton near the spill would probably

� ~~~be killed by direct contact or uptake of hydrocarbons. Recovery of com-

mon species such as Eurytemora affinis and Acartia tonsa would probably

U ~~~be rapid due to recruitment from adjacent systems, but subsequent zoo-

plankton populations may be reduced from normal levels and continue to

experience sublethal effects. Populations of motile organisms which de-

3 ~~~pend upon the plankton and other food resources within the bay would

decline. Catches of commercially important fishes, forage fishes, crabs

U ~~~and shrimps would also drop. Recruitment would be slow due to deaths of

larvae (particularly of decapods and fish). Adults of the motile forms

like the blue crab and numerous fishes might leave the bay and avoid

5 ~~~it as long as hydrocarbons remained. Organisms with sensory apparati

affected by the hydrocarbons might continue to enter the bay, only to

3 ~~~suffer sublethal effects caused by hydrocarbon uptake and ingestion.

Bird populations in the area would be severely damaged even by a

small spill, with dramatic mortalities of white ibis, pelicans, cormor-
3 ~~~ants, gulls and terns, waders and divers. Those which survived or avoided

direct oiling would suffer sublethal effects such as nervous disorders

5 ~~~or reduced reproduction due to ingested oil. Predatory birds, including

the bald eagle, peregrine falcon and osprey, would suffer sublethal

I ~~~effects from ingestion and concentration of hydrocarbon fractions.

In short, even a brief review of the oil spill literature indicates

3 ~~~that an estuary like Winyah Bay would suffer severe negative impacts if

10-21

an oil spill occurred. Data from the one long-term study of such a spill3

in a marsh area (Sanders et al., 1980) indicate that recovery would take

many years, and complete recovery may never occur.3

Whereas acute poisoning of organisms from oil or chemical spillsI

is relatively simple to detect, sublethal effects of chronic or low-3

level inputs of hydrocarbons may not become apparent for years or decades.

The chronic pollution of upper Winyah Bay, especially the Sampit River,

by local industry has already caused extensive damage to benthic com-

munities in this area. Oil droplets discharged into silt-laden, slow-I

flowing waters would accumulate on the bottom in the form of an oily

sludge. The rate at which oiled sediments would build up and spread in-

to the adjacent bay would be difficult to predict; however, very low3

levels of hydrocarbons have been shown to cause numerous sublethal ef-

fects in many benthic, epibenthic, planktonic, and intertidal estuarineI

organisms, and there is no reason to expect anything different in Winyah

Bay.

The data obtained during this study indicate that although Winyah3

Bay continues to support populations of shrimps, crabs, and fishes, the

diversity and abundance of organisms is surprisingly low, especially in3

the upper bay. These observations suggest that present levels of stress

may be adversely affecting the health and future of Winyah Bay as a

functional estuary. The implications of the deterioration of Winyah Bay3

to commercial and recreational fisheries in the future are not good,

and the consequences of increased petroleum-based energy development5

in this estuarine area could be serious and long-lasting. The following

quote from the National Academy of Sciences report on petroluem inI

marine environments (1975; p. 86) provides an articulate conclusion to3

10-22

3 ~~~this report, and should be pondered by decision-makers concerned with
future development in Winyah Bay:
3 ~~~~"The soluble fractions of petroleum probably are the most
harmful to marine organisms. These undoubtedly make up
the bulk of the oil that enters the coastal waters as co-
product brines and refinery effluents. Such discharges,
particularly when they occur in estuaries, may pollute
the shallow water areas that serve as nursery areas for
many coastal marine biota. These waters ordinarily are
U ~ ~~~subject to extremes of temperature, and where tidal
fluctuations are small, flushing of the bays and disp-
ersal of wastes may be slow. These characteristics of
I ~ ~~~estuaries may combine with the chronic introduction of
oil wastes... .to intensify biological effects.
"In addition, the slow dispersal of oil in some est-
uaries can increase adsorption onto suspended particulate
matter. When these suspended particulates are incorpor-
ated in the sediments, the exposure of benthic organisms
to oil is increased. The high biological productivity of
3 ~ ~~~estuaries ensures the exposure of many organisms to the
wastes, particularly in the sensitive stages of their
life history. Synergistic interactions between extremes
I ~ ~~~of temperature and salinity and oil may aggravate del-
eterious effects. Therefore, because they combine biol-
ogical productivity with the most severe exposure to
wastes, estuaries are most vulnerable to the serious
effects of chronic oil pollution."

I~~~~~~~~~~~~~02

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