Impacts of a mechanical harvester on intertidal oyster communities in South Carolina final report

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

SOUTH CAROLINA MARINE RESOURCES CENTER

SH
371
.I47
1985

Property of CSC Librazry

IMPACTS OF A MECHANICAL HARVESTER

ON INTERTIDAL OYSTER COMMUNITIES

IN SOUTH CAROLINA

FINAL REPORT
Coastal Energy Impact Program
Contract #CEIP-83-06
Project #30357

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

1 January 1985

Prepared by:

John J. Manziu
Victor G. Burrell, Jr.2
Kathryn J. Klemfnowicz
Nancy H. Hadley3
John A. Collier

IMarine Resources Research Institute
P.O. Box 12559
Charleston, SC 29412

2Grice Marine Biological Laboratory
College of Charleston
Charleston, SC 29412

3Agriculture Engineering Dept.
Clemson University
Clemson, SC 29631

us.

* 4

TABLE OF CONTENTS

List of tables ...... ............. .iii

List of figures ...............iv

Abstract ...................

Introduction ......................2

Methods e * *e .**...........5

Field sampling ........................ 5

Data analysis ......... .................

The harvester 9 .............................9

Results and discussion..............................10

Oyster population parameters............ .... ....10

Encrusting and non-motile invertebrates ......... ..14

Quantitative analysis of motile

and non-colonial invertebrates...................18

Summary and conclusions .......... .... .25

Acknowledgements. .............. ...........28

References ......................... .............29

Tables.. 32................... 32

Figures ..................39

Appendix A ............................................44

LIST OF TABLES

1. Mean biomass (kg/m2) of oysters (wet weight) from five sample
quadrats collected at each strata by sampling period.

2. Immediate post-harvest sample quadrats taken from "disturbed" and
"undisturbed" areas of the harvest site.

3. Estimates of oyster set (as number of spat per gram of cultch) in high
and low intertidal areas of both harvested and control oyster reef sites
(a) and both in and adjacent to harvester "tracks" at the harvested site
(b).

4. Rank by occurrence of encrusting and non-motile invertebrate species
collected for all2sampling periods at all strata. Percent was computed
from 120 0.0625 m quadrats in which a taxon was present.

5. Frequency of occurrence (Z) for encrusting and non-motile invertebrates
for each stratum at each site. Frequency was computed as percent of five
quadrats analyzed for each temporal variable in which a taxon was
present.

6. Motile and non-colonial invertebrates collected for all sampling periods
for all strata types.

7. Temporal community structure values [number of individuals, number of
species, diversity (HW), evenness (JW), richness (SR) and dominance
index (DI)] for pooled replicate samples of motile and non-colonial
invertebrates at each stratum.

LIST OF FIGURES

1. Location of harvest and control sites in Beaufort County, South
Carolina.

2. The Clemson mechanical oyster harvester prototype, showing configuration
of the harvester head and the head control system

3. Total number of encrusting and non-motile species collected at each
strata for each sampling period.

4. Species density of motile and non-colonial invertebrates vs. oyster
biomass (kgl) for five 0.0625 m2 quadrats taken from high and low
intertidal strata at both harvest and control sites for each sampling
period (Pearson's product-moment correlation coefficient,o(O0.01,
rc=0.561).

5. Total number of individuals of the numerically dominant species
collected in pooled replicate samples from each stratum/site during each
sampling period.

ABSTRACT

An intertidal oyster reef in South Carolina was subjected to
mechanical harvesting to assess the effects of such activities on
oyster reef communities. Oyster population parameters in the high
and low intertidal strata of the experimental reef and an adjacent
control site were compared before and immediately after mechanical
harvesting and then monitored over an annual cycle to determine
long-term effects. Macrofaunal invertebrates associated with the
oyster beds were studied over the same time period. Subsequent to
mechanical harvesting, oyster biomass in the high intertidal
portion of the harvested reef remained low relative to the control
site, but biomass in the low intertidal area of the reef increased.
This was attributed to displacement of oysters from the upper reef
to the low intertidal area and to increased mortality in the upper
portion of the reef as a result of physical disturbance. Total
spatfall was lower on the harvested reef than on the control as a
result of reduced space (cultch) available for oyster set.
Encrusting and non-motile invertebrates appeared to be little
affected by the harvesting activities. The number of motile or
non-colonial invertebrate species present on the reef was not
affected by harvesting, but the species density was reduced in the
high intertidal stratum. Species density was correlated with oyster
biomass; thus, reduced density in the high intertidal zone
reflected the lower oyster biomass after harvesting. Community
diversity was also affected, with the high intertidal zone showing
increased diversity and decreased dominance, while the low
intertidal area had decreased diversity and increased dominance.
These changes were attributed to migration of some species from the
high intertidal portion of the reef to the low intertidal area.
This could be due to loss of habitat in the high intertidal zone or
be an opportunistic response to translocation of damaged oysters to
the low intertidal area. The effects of the mechanical harvester
appeared to be primarily related to reduced biomass in the high
intertidal area of the oyster bed. This resulted in increased
mortality of remaining oysters, decreased habitat for associated
invertebrates, and lower spat recruitment. Returning oyster shell
to the reef after harvesting would largely ameliorate these
effects.

INTRODUCTION

Populations of the American or eastern oyster, Crassostrea virginica

(Qmelin), in the coastal areas of the South Atlantic Bight, generally occupy

the intertidal zone where they form intertidal oyster rocks, grounds, or

reefs consisting of dense concentrations of shell, live oysters, sediments

and associated biota. These beds are often supported on a matrix of sediment

and shell resulting from decades of interaction between oyster populations

and the large quantities of particulates characteristic to the estuarine

milieu of the Southeast. Periods of tidal inundation determine the landward

and aerial extent of the intertidal oyster bed while predation and siltation

appear to limit oyster populations in the lower intertidal and subtidal areas

(Bahr and Lanier, 1981). In South Carolina, the dominance of the oyster bed

as a characteristic of estuarine topography was noted as early as 1892 by

Dean (as cited in Bahr and Lanier, 1981) who commented that oyster "ledges"

in many localities "have formed vast oyster flats, acres, sometimes miles, in

extent." In fact, it has been estimated that 95% of the oyster population in

South Carolina is intertidal (Gracy and Keith, 1972; Dame, 1979).

Harvesting intertidal oysters in South Carolina has traditionally been a

hand labor activity. In recent years, however, the economics of the oyster

industry and the initiation of federal and state social programs have made it

increasingly difficult to recuit workers for this seasonal hand labor pool

(Gracy and Keith, 1972). The mechanical harvesting of intertidal oysters is

being considered as a realistic alternative to augment this dwindling labor

supply. Anticipated benefits accruing from the development of mechanical

harvesting include:

1. Increased utilization of oyster growing areas as harvesting becomes

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less labor dependent.

2. Increased landings because the harvester will supplement hand labor

and would permit gathering oysters throughout the tidal cycle.

3. Transplanting of polluted oysters to clean areas for deputation may

become practical with the efficiency of a mechanical harvester.

4. Efficient cultivation methods could be initiated with the ability to

move seed oysters mechanically.

The immenence of mechanical harvesting of intertidal oysters in South

Carolina creates several pertinent problems. Perhaps the foremost of these

concerns the effects of mechanical harvesting on water quality and itegrity

of benthic communities. While structurally substantial integrity, the oyster

beds and supporting matrices are, in fact, in fragile balance with

environmental factors. Traditional hand harvesting of intertidal oysters has

done little to interrupt this balance. The advent of mechanical harvesting,

however, has the potential of seriously jeopardizing intertidal populations

by not on-ly physically challenging the structure of oyster reefs but also by

increasing local water silt loads and thus damaging beds adjacent to those

being harvested.

The high degree of interest within the state for the development of a

mechanical harvesting protocol for intertidal oysters and the development of

the necessary hardware (through Clemson University) made it appropriate to

environmentally assess the mechanical harvesting of oysters in South Carolina

estuaries. This information is essential, not only to management agencies

(i.e., S.C. Department of Wildlife and Marine Resources) and regulatory

agencies (i.e., S.C. Coastal Council and Dept. of Health and Environmental

Control), but also to the oyster industry which must evaluate the

cost/benefit relationship of mechanization. Previous research involved the

design and development of the Clemson University oyster harvesting head, the

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basic components of which are a detachment head conveyor and a pickup

conveyor. Completion of the prototype harvesting system (which includes a 48

ft. vessel, escalator system, and harvesting head) was accomplished in May

1981.

A short term investigation to assess environmental perturbation by the

prototype mechanical oyster harvester developed by Clemson University was

completed in September 1981 (Manzi and Burrell, 1981). Sufficient

information to allow the formulation of definitive recommendations for

managing the use of the machine was not derived because of the short duration

of the study. The harvester sank after an initial harvest aud replant and

was not salvaged in time to complete planned tests. The single trial was

monitored for ten weeks and the results indicated that survival and growth of

transplanted stocks were satisfactory and that excessive sedimentation did

not occur in surrounding oyster beds at either the harvest or reception

sites. These data supported continued development of the Clemson machine,

but could not be used to make management decisions without additional

intensive and long term trials.

A study was funded by the Coastal Energy Impact Program in January 1983

to help provide information for formulation of appropriate management

policies. The planned experimental design included two spatial variables,

harvest and control sites and high and low intertidal strata, considered over

three temporal variables:

1. Pre-aarvest sampling to provide baseline information on preharvest

conditions,

2. Post-harvest sampling to determine immediate effects of mechanical

harvesting,

3. Long-term sampling to assess harvest effects over time and season.

METHODS

Field samIflinI

A harvest site and a control site were selected in the Coosaw River

drainage basin in Beaufort County South Carolina (32'3030"N, 80'40'35"W)

(Figure 1). The harvest site, situated on the south bank of the Coosaw

River, was approximately 75 meters long and 16 meters wide. The mean

elevation of the bed above MLW was 0.48 meters. The control site, located on

the west bank of McCally's Creek, was approximately 0.16 km from the harvest

site. This area was chosen because of its proximity and overall physical

similarity to the harvest site. In addition, this siz: was located within an

area where oyster picking was prohibited. This ensured its minimal

disturbance of the control site by the public throughout the duration of

study.

Samples for macrofaunal community analysis were selected using a

stratified random method with the upper and lower intertidal zones designated

as major strata. Samples for estimating oyster recruitment were collected

randomly, first from observed harvester "tracks" and then from unharvested

areas immediately adjacent to the sampled "track-". Samples for establishing

seasonal and pre- and post-harvest oyster population parameters

(length-frequency distributions, condition index and liveldead ratios) were

obtained by random selection of bed stock in bushel quantities from both

mechanical and hand harvesting activities. The following schedule of sample

collection for community analysis was observed:

Pre-Harvest Sample - early March 1983

Immediate Post-Harvest Sample - late March 1983

Spring Sample - April 1983

Summer Sample - August 1983

Fall Sample - November 1983

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Winter Sample - February 1984

Length frequency relationships were calculated from composites of 6 one-

bushel samples per sampling period (a minimum of 300 observations). Ratios

of living to dead (tissue present or no tissue but still articulated) oysters

were determined from the same bushel samples. A condition index, calculated

as a tissue percentage of total shell cavity volume, was determined on two

subsamples of the six bushel sample. In addition to the sampling schedule

indicated above, bushel samples for establishing population parameters were

collected in all intervening months between March and August 1983.

Macrofaunal communities were sampled at Lhe harvest and control sites,

using a grid coordinate system to randomly select five 1-m2 areas from

the two major strata (high and low intertidal). Within each area, a sample

was taken using a stainless steel circular quadrat frame which was 21 cm

deep and encompassed an area of 0.0625 m2. This frame was pressed into

the oyster bed to an approximate depth of 16 cm. The enclosed volume,

including oyster clusters, dead shell and other substrate, was removed by

using a post-hole digger. In situ temperature and salinity measurements

were taken subtidally at the water's edge of each site during each sampling

period (Appendix A).

Each sample was sealed in a 19-liter plastic bucket and returned to the

laboratory where it was washed and sieved through a 0.5 mm stainless steel

screen. The material retained by the sieve was preserved in 10% formalin and

stained with rose bengal. The biological material was then sorted under a

dissecting microscope and all invertebrates were enumerated and identified to

the lowest taxonomic level possible. After sieving, all living oysters

larger than 1.8 cm were counted and weighed to determine live oyster biomass

(wet weight) for each sample. From this live portion, all oysters were

examined for encrusting and non-motile invertebrates. Because of the

~~~I ~~~~~~~~-7-

difficulty of quantifying these types of organisms only the presence or

absence of species was noted after identificaton.

Data Analysis

Ovster biomass The biomass of all living oysters greater than 18 mm

(longest dimension) was obtained for each sampling period as an average

estimate per 0.0625 m2 sample by pooling data from the five replicate

samples taken from each stratum. Normality of data was determined by log-log

graphic analyses of means and variances (Elliot, 1977) and homogenity of

variances was indicated for all strata types for all sampling periods using

Barlett's test and Scheffe-Box test (Sokal and Rohlf, 1981). Difference in

mean oyster biomass between two samples was determined by the two sample

t-test (Sokal and Rohlf, 1981). Model I two-way analysis of variance (Sokal

and Rohlf, 1981) was used to determine whether total oyster biomass differed

significantly between strata types and temporal variables. Subsequently, the

Scheffe, Tukey Kramer and T-methods of a posteriori unplanned comparisons

(Sokal and Rohlf, 1981) were used to indicate significant differences among

strata types for each temporal variable.

Oualitative Assessment of Encrustine and Non-motile Invertebrates

Qualitative data taken from encrusting and non-motile invertebrates found on

the living portion of oysters in a sample were compared based on the number

of species, frequency of occurrence of individual species, and total

occurrences per sampling period. The Kruskal-Wallis one-way analysis by

ranks (Siegel, 1956) was used to determine significant differences between

temporal and spatial variables. The Mann-Whitney test (Daniel, 1983) was

used to determine significant differences between all two-sample comparisons.

Quantitative Assessment of Motile and Non-colonial Invertebrates Data

were analyzed to determine all temporal and spatial changes in species

density, diversity and dominance. To obtain a larger sample size and more

representative estimate of species composition for each stratum, data from

replicate samples at each site were pooled.

Species density measurements were calculated as the mean number of

individuals per 0.0625 m2 based on replicate samples from each stratum

for each sampling period. Relative abundance of individual species was

determined from the total number of invertebrates collected in all replicate

samples from each stratum for each sampling period.

Species diversity was estimated using the Shannon index for community

diversity (H'), species evennes (J') (Pielou, 1975) and species richness

(SR) (Margalef, 1958). Annual estimates of species diversity or composition

for each strata type at both harvest and control sites were taken as means

over six sampling periods. The degree of dominance in each stratum for each

sampling period was quantified from pooled replicates using the dominance

index (DI)(McNaughton, 1967). The rejection level for the null hypothesis

used for all statistical tests in this study was 95% (co= 0.05).

The Harvester

The harvester vessel is a steel hull pontoon design, 16 meters long.

Two pontoons, each 1.55 m wide and 0.9 m deep, are separated by 1.85 m. The

steel for the pontoons is 5 mm flat plate coated on both sides with coal tar

epoxy. The vessel is powered by two 86 Kw outboard engines which can operate

in water as shallow as 0.6 meters.

The prototype harvester head consisted of 2 sets of rotating tines, 1.2

m wide (see Figure 2). The first set of tines rotates in the direction of

travel and dislodges the oysters from the bottom. The second set rotates

opposite the direction of travel and picks the oysters up from the bottom.

The oysters are directed onto a steel pan where a water jet transfers them to

the escalator conveyor. Oysters are then transferred to a cross conveyor and

loaded on a barge adjacent to the harvester. The rotating tines and the

conveyor are powered with hydraulic motors run by a 125 Kw diesel engine.

One of the major objectives of this research was to develop a machine

that would have minimum impact on the shell matrix or beds. The head and-

escalator conveyor would exert a force of over 6,000 Newtons if they were

allowed to bear directly on the bottom. This would cause excessive damage in

soft areas. An automatic control system was developed to maintain a constant

preset force on the bottom through depths varying from 1 to 3 meters. The

cable supporting the head was looped around a shieve on the rod of a

hydraulic cylinder and then attached to a winch (see Figure 2). Pressure

from the hydraulic system is reduced in a valve to a preset pressure and

applied to the cylinder. Therefore if a bottom force of 2,000 Newtons is

desired, a pressure to pull 4,000 Newtons on the cable is applied to the

cylinder, leaving 2,000 Newtons to be supported by the bottom. As the water

depth changes, the pressure reducing valve either adds or dumps oil from the

cylinder to maintain a constant pressure. The cylinder has a control range

harvest site had not decreased significantly from preharvest collections,

biomass in both high and low intertidal strata of the harvest site was

significantly lower than in corresponding control strata.

Oyster biomass is obviously a prime variable to reflect physical

disturbance caused by the harvester. Immediately after the harvesting

operation, the physical effects varied within the harvest site, with some

areas appearing "undisturbed" while other reef areas had tracks and deep

depressions caused by the mechanical harvester. Although randomization in

sampling design was maintained for all sampling periods to determine the

unbiased effects of harvesting on the oyster reef community, it was noted

whether immediate post-harvest samples were taken from disturbed or

undisturbed areas of the harvest site. No marked difference in mean oyster

biomass was found between these samples (Table 2).

Seasonal fluctuations in mean oyster biomass at the harvest site were

dissimilar to those at the control site for both high and low intertidal

strata (Table 1). In pre-harvest collections, greater oyster biomass was

found in high intertidal strata at both sites. For all sampling periods

after the harvesting operation, mean oyster biomass was highest in the high

intertidal stratum of the control site. Spring samples showed that oyster

biomass had increased for all strata types at both sites; however, biomass at

both harvest high and low strata were lower than preharvest values. Oyster

biomass in the high intertidal area of the harvest site remained low after

harvesting compared to the control site. Biomass in the low intertidal

stratum of the harvest site, however, was greater than in the control during

summer, fall and winter, although these differences were not statistically

significant (Table 1).

The summer sampling period showed a decrease in biomass values at both

sites except for an increase at the harvest low stratum above that of the

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of 0.8 meters, so limit switches near the end of the cylinder stroke trigger

the winch to center the system automatically. This expands the automatic

range to 3 meters. The harvester head was modified in the fall and winter of

1983. The resulting design, used in harvesting the areas studied in this

project, had only a single set of rotating tines.

RESULTS AND DISCUSSION

Oyster DoDulation Darameters

Approximately 600 bushels of oysters were harvested by the mechanical

harvester at the Coosaw Island site on March 15 & 16, 1983. A pre-harvest

survey by the South Carolina Wildlife and Marine Resources Department's

I Intertidal Oyster Survey Program (W.D. Anderson, personal communication)

indicated that three density classifications characteristic to the harvest

site had average total shell densities of 18.9, 35.6 and 24.2 US

bushels/m2. This converted to 1.7, 4.6 and 3.8 bushels/m2 of live

oysters, respectively. A redundant survey performed approximately 6 weeks

after harvest indicated remaining average total densities of 0.21, 0.14 and

0.31 bushels/m2 along the three strata. These surveys permitted an

estimate of harvester efficiency by comparing "before and after" survey

results. The resulting estimates, ranging from 87.6% to 96.9%, appear high

from both subjective observations of the site and from the more objective

estimates of biomass made on the harvest site.

Preharvest samples at the control and experimental sites showed greater

mean oyster biomass in the high intertidal strata than in the low, although

differences were not significant. Immediate post-harvest sampling indicated

that mean oyster biomass had decreased in both high and low intertidal strata

of the harvest site (Table 1). At this time, the control site had slightly

higher mean biomass estimates for the high intertidal stratum and showed no

change for the low intertidal stratum. Although mean oyster biomass at the

~~~~~~~~~I . ~-12-

preharvest value. One explanation for this increase could be the physical

displacement of oyster clusters to low intertidal boundaries by the

harvesting operation. Oyster clusters lying just above the low intertidal

boundary may have eventually contributed remaining live oysters to the low

intertidal stratum. Predation and siltation in the lower intertidal area

would eventually cause increased oyster mortalities. Marshall (1954) found

that oysters taken from an intertidal oyster bed and placed below mean low

water exhibited 91% mortality, which he attributed to predation between the

months of August and November in Florida. Dunnington (1968) recorded

increased mortality of buried oysters with increased temperature.

Summer oyster biomass for the high intertidal stratum of the harvested

site was significantly lower than the control. Bahr and Lanier (1981)

reported that high oyster mortalities in the summer could occur if the

angular orientation of reef oysters which provides shading to protect oysters

was disrupted. The harvesting activity may have disrupted the mutual shading

of crowded reef oysters at the harvest site; consequently, higher mortality

due to increased summer temperatures would cause lower biomass. Biomass at

the high intertidal harvest site continued to decrease throughout the summer

and early fall and was significantly lower than biomass at the corresponding

control site. Biomass estimates for the low intertidal areas of both sites,

however, were not statistically different over the same time period.

One possible explanation for continued low biomass in the high

intertidal atratum following harvest could be reduction in the intensity of

oyster set. Oyster set occurs almost continuously from May to

September/October (Lunz, 1954; SC Marine Resources Division, unpublished

data) in South Carolina, and a decrease in biomass might reflect the failure

of a site to attract set. Samples were taken in November 1983 to determine

spatfall at the two sites. Table 3a indicates that there were no significant

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differences between sites for samples from either stratum. At both sites,

significantly higher numbers of spat occurred in the high intertidal zone,

compared to the lower stratum. In estimates of spatfall both within the

obvious "tracks" of the harvester and in adjacent "undisturbed" areas of the

harvested site (Table 3b), no significant differences could be discerned in

either low or high intertidal areas. The decrease in cultch within the

harvested tracks does, however, result in fewer spat per unit area of reef.

This may be the reason for different biomass estimates between the two sites;

i.e., the rate of spatfall was similar, but total spatfall reflected

differences in available cultch.

The final winter sampling period, almost one year after harvesting,

indicated an increase in oyster biomass in both harvest and control high

intertidal strata and a decrease in biomass in both low intertidal strata

(Table 1). Although winter biomass values were not significantly different

between low intertidal strata, biomass at the high intertidal harvest site

was significantly lower than the corresponding control.

The size-frequency distribution of the intertidal oyster population on

the harvest site was monitored monthly from March to August, 1983. A minimum

of six bushels of oysters were collected by hand monthly from the intertidal

reef. All live oysters were measured across their longest dimension and

tallied into size classes of 10-mm increments. Percentile size-frequency

distributions indicated little change in the reef population size structure

over the harvesting and initial recovery period. Pre-harvest samples

indicated a population mean size of 57.8 mm (s = 20.9 mm). Mean size

decreased immediately after harvest, but then increased and attained

preharvest values within three months. Size distribution on the harvested

reef indicated a slight, but not significant, bias toward smaller size

classes immediately after harvesting but the population distribution

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approached pre-harvest characteristics by mid-summer.

The initial decrease in population size after harvesting would indicate

some selection toward larger oysters by the mechanical harvester. Samples

taken from the harvester during the harvesting operation indicated a mean

population size of 63.4 mm (s = 20.9), about 5.5 mm larger than the mean

population size on the reef before harvesting. Since clusters receive

greater selection pressure from the harvester, and clusters contain a high

proportion of the larger live oysters, it is not surprising to find some size

selection evident in mechanical harvesting. Changes in population

size-frequency distribution after mechanical harvesting did not appear to be

mortality related. Samples taken from the harvester during operation

indicated less than 1X damage to the harvested populations. In post-harvest

samples taken directly from areas disturbed by the harvester (i.e., harvester

"tracks"), less than 3% of the remaining oysters were noticably damaged.

Encrustin2 and Non-Motile Invertebrates

A total of nine encrusting and non-motile invertebrate species were

collected in this study: the protozoan spirotrich Folliculina sp.; the

sponges Cliona celata. Cliona vastifica. Craniella sp., and Haliclona

loosanoff; the anthozoan Aiptasia pallida: the bryozoans Membranipora

tenuis and SchizoDorella errata: and the barnacle Balanus eburneus. Based

on percent occurrence in all strata types over all sampling periods combined,

M. tenuis was the most commonly occurring species found in 54 (45%) of the

120 samples (Table 4). Other frequently occurring species were B. eburneus

(40.8%), Folliculina sp. (36.7%) and the boring sponge Cliona celata

(24.2%). The remaining species occurred relatively infrequently, while H.

loosanoff was found in only one collection taken in the low intertidal area

of the control site during the winter.

In South Carolina, Cliona spp. are considered to be one of the most

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serious oyster pests (Lunz, 1935). Hopkins (1956) examined oysters from

several South Carolina areas for the presence of Cliona spp. and found over

90% occurrence in areas near the present study site. Folliculinid species are

associated with oysters from a wide range of geographic locations and their

large size make them an obvious component of the intertidal oyster community

(Andrews, 1944; Wells, 1961). The barnacle B. eburneus is predominantly an

intertidal organism (Zullo, 1963) and has been reported to be the most

serious fouling organism in Beaufort, North Carolina (McDougall, 1943).

Wells (1961) reported M. tenuis. B. eburneus, Follucilinid species and C.

celata to occur in more than 40% of collections taken from oyster beds in the

vicinity of Beaufort, North Carolina. In view of their reported importance

to the oyster reef community, serious consideration was given to fluctuations

in dominant encrusting and non-motile species (i.e., M. tenuis. B.

eburneus, Folliculina sp., and C. celata).

Soecies Comoosition Preharvest analyses of encrusting and non-motile

invertebrate species indicated similar species compositional patterns at the

harvest and control sites for both high and low intertidal strata. The

number of encrusting and non-motile species collected one week after the

harvesting operation showed little change in species composition (Figure 3).

Number of species in both strata of he control site increased in comparison

to the harvest site, but the median number of species was not significantly

different between sites. In addition, comparison of samples taken from the

harvest site indicated no significant difference in species composition

between areas disturbed by the harvester and relatively undisturbed areas of

the same site (Table 2).

Based on long-term analyses subsequent to the harvesting operation the

following generalizations can be made concerning the number of encrusting and

non-motile species for all seasonal sampling periods (with the exception of

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the control low intertidal strata for the summer sampling period):

1. Species number in the low intertidal stratum was generally greater

than in the high stratum at both sites;

2. All species occurring in > 20% of harvest high and low intertidal

strata were also found in respective control collections;

3. Species number for both harvest strata types was consistently lower

than control strata.

Although fewer species were generally found in both strata of the harvest

site than in the orresponding control strata, comparisons between sites

revealed no significant difference in species numbers. Comparison of summer

samples from the low intertidal strata showed a greater species number at the

harvest site than at the control (Figure 3). Many ecological studies have

determined that distribution of attached epibenthic organisms is limited by

competitive interaction for space (Connell, 1961; Gordon, 1972; Lang, 1973;

Jackson, 1977). During the summer the low intertidal stratum of the harvest

site had higher oyster biomass than the control site. This difference was

attributed to effects of mechanical harvesting. Greater oyster biomass would

provide more surface area for colonization by other invertebrates, possibly

explaining the higher number of species in the low intertidal stratum of the

harvested site during the summer. However, statistical analyses revealed no

significant correlation between species number or frequency of occurrence of

encrusting and non-motile species and oyster biomass.

Freauencv of Occurrence Although mechanical harvesting did not appear

to affect species richness it may have caused a decline in the frequency of

occurrence of encrusting and non-motile invertebrates, particularly in high

intertidal areas. The total number of occurrences of encrusting and

non-motile species in pre-harvest pooled replicate samples for each stratum

indicated no statistically significant difference between harvest and control

-17-

sites. Slightly greater values were indicated for the low intertidal stratum

compared to the high intertidal stratum at each site (Table 5). Immediate

post-harvest analyses found little change in number of occurrences between

harvest and control strata types. In addition, there was no significant

difference in the number of encrusting and non-motile species occurring on

physically disturbed and on relatively unaffected areas of the harvest site.

Long-term analyses indicated fewer species occurrences in the harvest high

intertidal stratum than in the control for almost all sampling periods. The

one exception was during the fall, when no species were found at either site.

Due to the contagious distribution of these species, however, it is difficult

to determine whether fewer occurrences at the harvest site are due to

patchiness or to effects initiated by the harvesting activity.

Before the harvesting operation, M. tenuis and B. eburneus occurred in

high intertidal samples from both sites. Individual species frequencies

indicated M. tenuis to be most common in preharvest high intertidal

collections at both harvest and control sites. Immediately after the

harvesting operation, Folliculina sp. and B. eburneus were collected at the

harvest high intertidal stratum while both these species in addition to M.

tenuis, Craniella sp. and the anthozoan Aiptasia pallida occurred in the

control high intertidal stratum. The absence of M. tenuis from the

harvested site could be attributed to the normally patchy distribution of

this species and no related to harvesting activity. The increased frequency

of Folliculina sp. at the harvest site, compared to preharvest collections,

may have resulted from rapid colonization immediately after the harvesting

activity, although this can not be directly attributed to harvest effects

since Folliculina sp. was also relatively common in high intertidal

collections at the control site.

Long-term analyses over seasonal variables indicated that MembraniDora

tenuis and Folliculina sp. occurred less frequently among the four top

ranking species in the high intertidal stratum'at the harvest site than at

the control site (Table 5). The contagious distribution of these species for

all strata types suggests that these observed differences between harvest and

control sites may not be directly attributed to the harvesting activity. For

low intertidal strata, no significant difference was noted in terms of the

top four ranking species between harvest and control sites over seasonal

intervals. The presence of the boring sponge C. celata at both low

intertidal areas and relative absence from high intertidal strata indicates

that this species is primarily restricted to the low intertidal portion of

oyster reefs. No other encrusting or non-motile species found in this study

exhibited a distributional pattern unique to either high or low intertidal

strata.

Ouantitative Analvses of Motile and Non-Colonial Invertebrates

Soecies composition Eighty-nine motile and non-colonial invertebrate

species were collected during the course of this study (Table 6). While more

species have been reported in association with oyster populations in both

subtidal and intertidal areas (Wells, 1961; Maurer and Watling, 1973) the

number observed in this study is greater than previous reports from strictly

intertidal oyster reefs. Species number did not differ greatly between

harvest and control sites. While annual species counts for high intertidal

strata were 55 and 59 for harvest and control sites, respectively, 45 species

were common to both sites. More species were found in the low intertidal

area of both sites over an annual cycle (a total of 65 and 67 species at the

harvest site and control sites, respectively), and 50 species were common to

both sites. Maximum species numbers were recorded in winter collections for

-19-

both high intertidal strata, while minimum species numbers were found in

summer at the harvest high intertidal stratum and in fall at the control

site. For low intertidal strata, a maximum number of species was recorded in

preharvest collections at the harvest site and in immediate post-harvest

collections atthe control site. Minimum species numbers were found in summer

for both low intertidal strata. Temporal fluctuations in species number were

similar between high intertidal strata at both sites, except for the

immediate post-harvest sampling period. At this time, 32 species were

present at the harvest site while 42 species were present at the control

site. The harvesting operation apparently immediately modified the high

intertidal oyster reef community. Species recorded in preharvest samples for

the high intertidal stratum at the harvest site and absent one week after

harvesting were primarily bottom-dwellers (e.g., A. iricolor, MolRula sp.,

caprellids and nemertines). The mean number of species collected over all

sampling periods was significantly lower for harvest low intertidal stratum

as compared to the control. Only during the final winter sampling period was

species number comparable at both low intertidal sites.

Eight species comprised more than 70% of the total number of individuals

collected during the study period: the pyramellid gastropod Boonea imoressa:

the polychaetes Streblospio benedicti, Nereis succinea and Phvllodoce

fragilis: the xanthid crabs EurvDanoneus depressus and Panopeus herbstii:

the amphipod Melita nitida: and the isopod Cassidinidea ovalis. Other

studies have found these species to be relatively abundant in intertidal

oyster reef communities (Wells, 1961; Dame, 1979; Bahr and Lanier, 1981). An

additional 16 percent of the total collection was comprised of oligochaetes

and nematodes. All eight species listed above were numerically dominant for

annual totals taken high intertidally at both harvest and control sites. In

addition, a halacaridean mite species was common high intertidally at both

-20-

sites and insect pupae were abundant at the harvest site but rare at the

control site.

Communitv Structure Species density, expressed as number of

individuals per unit area, was significantly different among strata types

over all sampling periods. Mean density over an annual cycle was greatest

for control high intertidal strata. Density in the high intertidal area of

the harvest site was less than half this value. Low intertidal densities

were similar for both harvest and control areas over an annual cycle.

Disturbance initiated by harvesting apparently had the greatest effect on the

high intertidal area of the harvest site. The decline in species density for

high intertidal strata was evident immediately after the harvesting activity.

An approximate 72% decrease in species density occurred at this time while a

29% increase was calculated for the control site. In all subsequent samples,

species density remained lower in the harvest high intertidal stratum than in

the control. Statistically significant differences were detected in summer

and fall collections. Although mechanical harvesting did not appear to

affect species density in the low intertidal area of the harvest site over an

annual cycle, species density at the harvested site immediately after the

harvesting activity was signficantly lower than the control. Species density

exhibited seasonal trends in both strata of both sites. In all sample areas,

maximum species densities were recorded during winter months and mininum

species densities in summer.

Species density was positively correlated with mean oyster biomass for

all strata types at all sampling times (Figure 4). This relationship

indicates the importance of living oysters to the oyster reef community. In

the undisturbed oyster reef, mean oyster biomass was greater in the high

intertidal area than in the low intertidal. Species density was

correspondingly high in this portion of the oyster reef. At the disturbed

-21-

harvest site, however, mean oyster biomass in the high intertidal zone was

reduced and species density was also diminished. While mechanical harvesting

appeared to have initially reduced species density at the harvest site, the

reduction in oyster biomass in the high intertidal stratum caused species

density to remain low. Oyster biomass and species density are usually lower

in low intertidal areas and therefore little change in species density was

found in this portion of the oyster reef. The major dominant species

collected throughout this study (B. impressa. N. succinea, S. benedicti,

P. fra2ilis. C. ovalis. M. nitida. E. depressus. and P. herbstii)

with he exception of S. benedicti , all exhibited direct correlation of

density with oyster biomass (p < 0.05, .Kendall's rank correlation

coefficient). At the control site, these species had higher densities in the

high intertidal zone. At the harvested site, oyster biomass was reduced in

the high intertidal area and these species had greater density in the low

intertidal stratum. Subsequently, the absence of these dominants contributed

to higher diversity, evenness and richness in the harvest high intertidal

area and their presence in the low intertidal stratum was reflected in lower

diversity, evenness and richness values.

The natural undisturbed oyster reef (control site) generally exhibited a

more diverse, even and richer species assemblage in the low intertidal area

(Table 7). Fewer individuals were distributed among more species, resulting

in a lower dominance by species in this area. In contrast, species

composition in the high intertidal area of the control site was indicative of

a more limited community assemblage. Lower diversity, evenness and richness

values for this stratum reflected high numerical dominance of species.

Seasonal variations, in combination with daily fluctuations due to tidal

action, create an extraordinarily stressful habitat in high intertidal areas.

Consequently, success in the high intertidal zone is limited to those species

-22-

capable of tolerating extreme fluctuations in environmental parameters; fewer

species are found but these may be abundant in numbers. At the harvest site,

in contrast, greater species diversity was found in the high intertidal area

than in the low intertidal stratum. A comparison between high intertidal

strata of the two sites indicated that diversity increased at the harvest

site immediately after the harvesting activity and was significantly greater

than at the control over the annual cycle. In the low intertidal area, the

control site generally had a greater diversity index over the annual cycle

than the harvest site. Maximum and minimum diversity peaks, however,

coincided between low intertidal strata; diversity was highest at both sites

in winter and lowest in summer.

Evenness and richness values were significantly different among all

strata types. Comparisons of high intertidal strata showed a more even

distribution at the harvest site over an annual cycle. Immediately after the

harvesting activity, species evenness for low intertidal strata had increased

at the control site while no change was noted at the harvest site.

Subsequently, evenness remained lower at the harvest site than at the control

area, especially in the summer. Low intertidal strata showed significantly

lower species richness at the harvest site than the control site. During the

fall a considerably less rich species assemblage was found for harvest low

intertidal stratum as compared to the control. Subsequently, species

richness increased in this stratum for the final winter sampling period and

was slightly greater than the control. Richness values were also relatively

high for high intertidal areas at both sites in winter. The increased

richness during this sampling period was attributed primarily to the seasonal

recruitment of numerous polychaete species.

Dominance indices were relatively high for all strata types over all

sampling periods. For all collections taken during this study, dominance

-23-

indices were at least 40 per cent and were attributed to a combination of any

two of the following species: B. impressa. S. benedicti, N. succinea.

E. depressus, oligochaetes and nematodes. Dominance indices, however, were

substantially different among strata types. High intertidal strata exhibited

lower dominance at the harvest site as compared to the control. Maximum and

minimum dominance indices coincided for both low intertidal areas; dominance

indices were greatest in the summer and lowest in the winter. The low

intertidal stratum at the harvest site had a slightly greater mean dominance

index for the entire study than the control site, but the difference was not

statistically significant.

Abundance of the numerically dominant species in the different sampling

periods is illustrated in Figure 5. Boonea imoressa and S. benedicti

exhibited obvious changes in abundance in response to harvesting,

particularly in the high intertidal strata. Populations of both species

diminished through the spring and summer at all strata of both sites. Both

species showed increased abundance with the onset of cooler temperatures and

winter samples of both species began to resemble pre-harvest conditions at

the disturbed site. While B. imoressa generally dominated all control high

intertidal collections over an annual cycle, the decrease in abundance of

this organism at the harvest high intertidal area was the primary factor

contributing to lower dominance indices for this stratum. The decrease in

oyster biomass in the harvest high intertidal stratum after harvesting

accounted for the decline in abundance of this oyster ectoparasite. At the

time of the immediate post-harvest sampling period, a peak dominance index

was found for control high intertidal collections but not for the harvest

site. This suggests that organisms which accounted for the high dominance

index at the control site (primarily B. impressa ) may have been affected by

the harvesting operation. In fall, dominance was also low in the high

-24-

intertidal stratum of the harvest site compared to the control. At this time

B. impressa constituted 47% of the total control high intertidal collection

but only 30% of the harvest collection.

A disturbed or altered community structure may be initially dominated by

opportunistic species characterized by relatively small size, high

reproductive potential and short life span (Grassle and Grassle, 1974).

Mechanical harvesting apparently caused a decline in abundance of S.

benedicti in the high intertidal areas, but may have allowed this species to

act opportunistically in the low intertidal area of the harvest site. In

spring, one month after harvesting, S. benedicti was the numerically

dominant organism in harvest low intertidal areas and abundance had increased

68% compared to the preharvest sampling period (Figure 5). In contrast, its

abundance did not increase in the control low intertidal stratum at this

time. Abundance of S. benedicti declined precipitously at all sites in the

summer. This pattern of rapid increase in abundance and dominance followed

by a sharp decline suggests an opportunistic strategy initiated by the

harvesting disturbance.

The polychaete, N. succinea. is very abundant in South Carolina benthic

communities (Harder, 1976). The high abundance of this species in summer for

all strata types (Figure 5) is in agreement with other studies on this

species (Bishop, 1974). The numerical dominance of N. succinea in immediate

post-harvest collections taken from harvest high intertidal areas did not

agree with the control site data. The numerical dominance of this species in

the harvest high intertidal area may be a response to scavenging activities

within a disturbed oyster reef community.

Abundance of E. depressus in all strata fluctuated over the sampling

periods (Figure 5). Maximum densities at the control site were recorded in

summer for high intertidal stratum and in fall for low intertidal stratum.

-25-

Numerical dominance of this species was high for both control strata in

summer, primarily due to decreased densities of other invertebrates

(primarily polychaetes). Lower abundance of E. deoressus was especially

noted in harvest high intertidal collections as compared to the control for

all sampling periods after harvesting. This decrease in abundance can be

attributed to the decline in oyster biomass caused by the harvesting

activity. Since fewer oysters were in harvest high intertidal areas this

suggests less food sources and available shelter to support a large

population of E. depressus in contrast to the control. In low intertidal

area of the harvest site, abundance of this species increased 46% in the

immediate post-harvest collection, compared with a 3% increase in the

corresponding control stratum. The increased abundance of E. depressus in

the low intertidal stratum of the harvest site may be attributed to

scavenging activities upon disturbed areas of the reef.

SUMMARY AND CONCLUSIONS

Although this study was not designed to determine harvester efficiency,

biomass data and mortality estimates provide some indications of the

selectivity and assault potential of the mechanical oyster harvester on

intertidal beds. The high intertidal portion of oyster reefs accounts for a

large portion of the reef biomass. In this zone, biomass decreased markedly

after mechanical harvesting. This suggests that the large oyster clusters and

clumps that typify high intertidal strata are more susceptible to mechanical

harvesting. Very low mortalities were directly attributable to the harvester

activities. Size frequency distribution data from pre- and post-harvest

samples indicated a harvester disposition toward larger individuals on the

-26-

oyster reef as a whole. Finally, an increase in mean oyster biomass on the

low intertidal strata immediately following harvesting suggests that oysters

were translocated toward the lower strata during the harvesting process.

Oyster biomass decreased in both high and low intertidal strata

immediately after mechanical harvesting. Subsequently, biomass in the low

intertidal zone increased to greater than pre-harvest values and remained

high relative to the control site. This is probably attributable to

displacement of oysters from the higher portion of the reef. In the high

intertidal stratum of the harvested site, biomass showed an increase one

month after harvest but did not attain pre-harvest values. In subsequent

months biomass in this stratum decreased. This decrease was attributed to

translocation of remaining oysters tj lower areas of the reef and to

increased mortality of remaining oysters during the summer as a result of

disruption of the reef structure. Increases in oyster biomass at both control

strata in fall samples was attributed to growth of summer spatfall.

Estimates of spatfall at harvested and control sites showed no

significant differences in rates of recruitment between the sites. At both

sites, spatfall was greater on high intertidal strata than on low intertidal

strata. Subsequent differences between biomass increases at the two sites

appeared to result from differences in total spatfall rather than in rates of

recruitment. Mechanical harvesting reduced the surface area available for

oyster set in the high intertidal portion of the reef, resulting in lower

total spatfall even though the spat per unit surface area was similar to the

control site.

The harvester appeared to have little effect on non-motile and encrusting

organisms. Encrusting species occurred more frequently in the low intertidal

strata than in the high strata, but only the boring sponge, Cliona celata

appeared to be limited to this area of the reef. The number of species found

-27-

in the low intertidal stratum of the harvested area during the summer was

higher than in the control area. This coincides with an increased oyster

biomass in this stratum but no significant correlation could be demonstrated.

Mechanical harvesting did not alter the number of species of motile and

non-colonial invertebrates found on the oyster reef, but species density in

the high intertidal stratum was reduced. This was correlated with reduced

oyster biomass on this portion of the reef as a result of harvesting

activity. Community diversity was affected by the mechanical harvester, with

the high intertidal portion of the reef exhibiting increased diversity and

evenness and decreased dominance, while the lower intertidal area exhibited

decreased diversity and increased dominance. A single species,the pyramellid

gastropod B. imDressa , may account for both of these changes. After

harvesting, this species became less abundant on the high intertidal stratum

and more abundant on the low intertidal stratum. This shift in distribution

might indicate a loss of habitat in the high intertidal zone or an

opportunistic migration to areas where damaged oysters were displaced.

The major effects of the harvester appear to be related to reduction of

biomass in the high intertidal portion of the harvested reef. This results in

increased mortality of remaining oysters, decreased habitat for associated

invertebrates, and lower recruitment due to limited space available for

oyster set. These effects might be largely ameliorated by returning oyster

shell to the high intertidal portion of a reef after mechanical harvesting.

ACKNOWLEDGEMENTS

We thank the staff of the Marine Resources Research Institute

particularly George Steele for supervising field sampling and aiding in

laboratory analyses, Karen Swanson for graphic arts, and Nancy Beaumont for

typing the manuscript. We also thank Bill Anderson and the staff of the

Oyster Survey Project for pre- and post-harvest surveys. The manuscript was

reviewed by Drs. E. Wenner, R. Van Dolah and P. Eldridge and we gratefully

acknowledge their comments and criticism. Special recognition is

acknowledged to Dr. E. Wenner who supervised the thesis development of the

junior author (K. Klemanowicz) whose graduate research formed the basis of

this report.

REFERENCES

Andrews, E.A. 1944. Folliculinids on oyster shells. J. Mar. Res. 5:

169-177.

Bahr, L.M. and W.P. Lanier. 1981. The ecology of the intertidal oyster

reefs of the South Atlantic coast: a community profile. U.S. Fish and

Wild. Serv., Off. Bio. Serv. Washington, D.C.15: 105 pp.

Bishop, J. 1974. Observations on the swarming of a nereid polychaete,

Neanthes succinea,. from the northern Gulf of Mexico. Proc. La. Acad.

Sci.37: 60-62.

Connell, J.H. 1961. The influence of interspecific competition and other

factors on the distribution of the barnacle Chthamalus stellatus.

Ecol. 42: 710-723.

Dame, R.F. 1979. The abundance, diversity and biomass of macrobenthos on

North Inlet, South Carolina, intertidal oyster reefs. Proc. Natl.

Shellfish. Assoc. 68: 6-10.

Daniel, W.W. 1983. Biostatistics: a foundation for analysis in the health

sciences. New York, N.Y.: John Wiley & Sons. pp. 401-405.

Dunnington, E.A., Jr. 1968. Survival time of oysters after burial at

various temperatures. Proc. Natl. Shellfish. Assoc. 58: 101-103.

Elliott, J.M. 1977. Some methods for the statistical analysis of samples of

benthic invertebrates. Freshwater Biological Association. Sci. Publ.

No. 25. 2nd ed. 156 pp.

Gordon, D.P. 1972. Biological relationships of an intertidal bryozoan

population. J. Nat. Hist. 6: 503-514.

Gracy, R.C. and W.J. Keith. 1972. Survey of the South Carolina oyster

- fishery. S.C. Wild. Mar. Resour. Dept. Tech. Rep. 3: 28 pp.

Grassle, J.F. and J.P. Grassle. 1974. Opportunistic life histories and

-30-

genetic systems in marine benthic polychaetes. J. Mar. Res. 32: 253-284.

Harder, H.W. 1976. Distribution and abundance of estuarine polychaetes of

South Carolina. Masters Thesis. Dept. Biology. College of Charleston.

92 pp.

Hopkins, S.H. 1956. The boring sponges which attack South Carolina oysters

with notes on some associated organisms. Contrib. Bears Bluff Lab. 23:

30 pp.

Jackson, J.B.C. 1977. Habitat area, colonization, and development of

epibenthic community structure. In Biology of Benthic Organisms. B.F.

Keegan, P.O. Ceidigh, and P.J.S. Boaden eds. Proc. 11th European Mar.

Bio. Symp. Pergamon Press. Oxford and New York. pp. 349-358.

Lang, J.C. 1973. Interspecific aggression by scleractinian corals. Why the

race is not only to the swift. Bull. Mar. Sci. 23: 260-279.

Lunz, G.R., Jr. 1935. Qyster pest control investigations 1935. A

preliminary report of the survey of the coastal waters of South
I~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Carolina. U.S. Bur. Fish., Washington. 5 pp.

. 1954. The general pattern of oyster setting in South

Carolina. Proc. Natl. Shellfish Assoc. 45: 47-51.

Manzi, J.J. and V.G. Burrell, Jr. 1981. Mechanical harvesting of oysters in

South Carolina. Final Report. S.C. Wild. Mar. Resour. Dept.,

Charleston, S.C. 8 pp. (unpublished).

Margalef, D.R. 1958. Information theory in ecology. Gen. Syst. 3: 36-71.

Marshall, N. 1954. Factors controlling the distribution of oysters in a

neutral estuary. Ecol. 55(3): 322-327.

Maurer D. and L. Watling. 1973. The biology of the oyster community and its

associated fauna in Delaware Bay. Delaware Bay Report Series V. 6: 97

PP-

McDougall, K.D. 1943. Sessile marine invertebrates at Beaufort, North

-31-

Carolina. Ecol. Monogr. 13(3): 321-374.

McNaughton, S.J. 1967. Relationships among functional properties of

California grasslands. Nature 216: 168-169.

Pielou, E.C. 1975. Ecological Diversity. New York. N.Y.: John Wiley &

Sons. 165 pp.

Siegel, S. 1956. Non-parametric statistics for the behavioral sciences. New

York: McGraw-Hill.

Sokal, R.R. and F.J. Rohlf. 1981. Biometry: The principles and practice of

statistics in biological research. San Francisco, CA: W.H. Freeman Co.

859 pp.

Wells, H.W. 1961. The fauna of oyster beds with special reference to the

salinity factor. Ecol. Monogr. 31: 329-266.

Zullo, V. 1963. A preliminary report on the systematics and distribution of

barnacles of the Cape Cod region. Marine Biological Lab., Woods Hole,

33 pp.

Table 1. Mean biomass (kg/m2) of oysters (wet weight) from five sample
quadrats collected at each strata by sampling period.

Harvest Control

Sampling High Low High Low
Intertidal Intertidal Intertidal Intertidal

Preharvest y 16.06 10.40. 20.74 9.28
s 7.92 5.87 7.50 6.64

Immediate y 6.56 4.48 23.68 9.28
Post-Harvest s 5.20 1.34 7.54 2.08

Spring 3 10.88 7.68 29.44 10.88
s 7.18 7.87 9.23 2.62

Summer F 7.04 11.52 22.72 2.24
s 4.32 8.58 9.82 3.11

Fall y 5.89 10.72 28.80 8.64
s 7.09 9.62 6.10 5.84

Winter y' 6.40 9.34 28.80 3.62
s 6.40 11.04 8.83 3.54

Table 2. Immediate post-harvest sample quadrats taken from "disturbed"
and "undisturbed" areas of the harvest site.

Oyster Encrusting and Motile and Non-Colonial
Biomass Non-Motile
(kg/m2) Invertebrates
No. No. No. Dominance
Species Individuals Species Index

Disturbed

High 0.8 1 81 13 69.14
Intertidal
14.4 2 292 16 51.37

Low 3.2 1 434 16 74.65
Intertidal
6.4 1 286 19 73.08

Undisturbed

High 6.4 1 326 18 54.60
Intertidal
3.2 1 229 20 52.40

8.0 1 247 18 59.92

Low 3.2 1 180 20 63.33
Intertidal
4.8 1 136 15 48.53

4.8 2 240 22 56.25

Table 3. Estimates of oyster set (as number of spat per gram of cultch) in
high and low intertidal areas of both harvested and control oyster
reef sites (a) and both in and adjacent to harvester "tracks" at
the harvested site (b).

a. Harvested Site Control Site

High Intertidal

Spat # Spat/g Spat # Spat/g

96 0.10 69 0.20
114 0.17 51 0.11
102 0.13 72 0.15
99 0.12 66 0.i15
121 0.15 90 0.20
110 0.28 59 0.09

y 107 0.16 68 Ol15

Low Intertidal

Spat 1 Spat/g Spat # Spat/g

29 0.10 44 0.09
133 0.05 38 0.11
57 0.08 58 0.04
64 0.07 53 0.08

y 71 0.08 48 0.08

b. Harvested Site

High Intertidal Low Intertidal
Spat/g Spat/g

Disturbed 0.13* 0.11

Undisturbed 0.15 0.10

*data represent mean spat per gram from a single one bushel sample.

Table 4. Rank by occurrence of encrusting and non-motile invertebrate
species collected fole a3.l sampling periods at all strata. Percent
was computed from 120- 0.0625 m2 quadrats in which a taxon was
present.

Species Count Percent

Membrani-ora tenuis 54 45.0

Balanus eburneus 49 4o.83

Folliculina Sp. 44 36.67

Cliona. celata 29 21.17

Craniella sp. 11 92.7

Cliona vastifica 4 3.33

Schizoporella errata 4 3.33

Aiptasia Da-Ilida 3 2.50

Hraliclona, loosanoff 1 0.83

Table 5. Frequency of occurrence (%) for encrusting and non-motile invertebrates for each strata. Frequency
was computed as percent of five quadrats analyzed for each temporal variable in which a taxon was
present.

Sampling Folliculina Cliona Cliona Craniella Haliclona Aiptasia Membranipora Schizoporella Balanus
Strata Period sp. celata vastifica sp. loosanoff pallida tenuis errata eburneus

Preharvest 0 0 0 0 0 0 60 0 0
Immediate 100 0 0 0 0 0 0 0 20
Harvest Spring 20 0 0 0 0 0 20 0 20
high Summer 0 0 0 0 0 0 0 0 10
Fall 0 0 0 0 0 0 0 0 0
Winter 40 0 20 0 0 0 0 0 hO40

Preharvest 0 40 0 0 0 0 20 20 40
Immediate 60 20 20 0 0 0 20 20 0
!Harvest Spring 20 60 0 0 0 0 100 0 0
low Summer 20 60 0 0 0 0 40 0 80
Fall 0 0 0 0 0 0 0 0 0
Winter 60 60 0 0 0 0 80 0 0

Preharvest 40 0 0 0 0 0 100 0 80
Immediate 60 0 0 20 0 20 80 0 80
Control Spring 80 20 0 0 0 0 100 20 80
high Summer h0 20 20 0 0 20 20 0 40
Fall 0 0 0 0 0 0 0 0 0
Winter 100 20 0 0 0 0 100 20 100

Preharvest 60 80 0 h0 0 0 0 0 20
Immediate 60 100 20 60 0 0 100 0 80
Control Spring 40 60 0 60 0 20 100 20 100
low Summer 0 0 0 20 0 0 0 0 0
Fall 0 0 0 20 0 0 0 0 0
Winter 80 40 0 0 20 0 60 0 60

Tab le 6. M otile, ad uou-c-olo-J-1 imwertabiates collected for all Sampingl
Pavia" far AU1 strata types.

Oadgs.adt Aa~d
I~~~~~~~~~~~~~~p Ialaasglda.
tsalacazi (Species a)
SITUaeC03"s NaLacaaud (species b)
SlpumcmLida (imid~eun lid)
Hollusca AMAm~

C"'Ithtonsis madm osczaaad (speales a)
Cochliolarea meti Oatzimwd (speries b)

a____ C~nOPoi secea
I~dbsp. SP.3pboaastosa (species b)
Littarlum, - Uaxapaaccoid (species a)

paidgypods D1iEm1A Sp.
Carbula Coattacta CIIAi Sp.
Geskoaxla demiases Tmanid~ad,

T& --gsp.Latcea .

Vinarum ~~~~~~~~~~Cassidialdea oval"
Iumftdaa (mmU~id"Wid)
Playbe~~~~ainche I ~Utea Immensea

Anamlida ~~~~~~~~~Abliod, "d

Ar ~LL zTiciolo Caraphius achermsicus
00iOLI QMtt OCM lagustre

exoa"!!= Luercan Pmleabestax
Haplacolooas xTasil-s Pbazoespballdas
Hateromascus filifogi a r m " st Ubhleri
Losbriuwege tenuis
~YiLcmnmtaDcp
Mannyunkla S p . ~ becerachadlis

Nes faclsea haommos u~stis
serals im'C-Inma ~ ~ ~ ~ erbtl

prcras fslts.� ptnrarscooas aw

scal _____ Uca usiat.
stvebla;~974nodlcti lummebt af ,i

poyfeso-etfd Caraaopagouldae
Oulachaeea, (widmldif led) insect pupaet

Table 7. Temporal commmity structure values [number of individuals, number
of species, diversity (H'), evenness (J'), richness (SR) and
dominance index (DI)] for pooled replicate samples of motile and
nan-colonial invertebrates at each strata.

Sampling No. No.
Strata Period Individuals Species H' J' SR DI
Prebarvest 4124 30 2.97 0.60 3.484 48.21
*Harvest High Iuediate 1175 32 3.37 0.67 4.385 45.11
Ianrti dl ~ Spring 1853 24 2.91 0.63 3.057 60.23
Summer 534 24 3.29 0.72 3.662 45.13
Fall 554 32 3.65 0.73 4.907 38.81
Winter 1539 40 3.28 0.62 5.314 49.97

Preharvest 2066 34 3.00 0.59 4.323 55.91
Hsmediate 1276 32 2.95 0.59 4.335 60.74
Intrertidal Spring 2017 34 3.02 0.59 4.337 49.33
,Suimer 897 27 2.54 0.53 3.824 65.44
Fall 1137 27 2.95 0.62 3.695 55:32
Winter 2563 49 3.63 0.65 6.116 40.23

Prebarvest 3927 31 3.06 0.62 3.625 51.26
.Immediate 5511 42 2.67 0.50 4.759 66.85
Control High Spring 3958 32, 2.76 0.55 3.742 58.31
Inttidal Smer 2588 32 2.78 0.56 3.945 60.05
Fall 2980 31 2.81 0.57 3.750 58.36
Winter 3890 41 2.82 0.53 4.839 64.50

I Peharvest 2610 45 3.41 0.62 5.593 '48.62
I�tediate 2197 39 3.65 0.69 4 938 45.70
Control Low Spring 1950 38 3.23 0.61 4.884 53.13
Intertida l Summer 741 37 3.21 0.62 5.448 54.52
Fall- -. 1453 38 3.41 0.65 5.082 48.86
Winter 1571 42 3.68 0.68 5.571 43.22

flAt 5 -,rfood . Ac.

I~~~~~~~~~~~~~~~� /I di.~~Q-;~~ Sa.'1
3~~~~

Pofk. Island

\A Jac Isla n d AL
- -A
I~~~~~~~~~~~~

3 L) -Jeytd =

Figure 1. Location of harvest and control sites in Beaufort County,
South Carolina.
55j o~~~~~~~~~~
*~ 'YZUA
I~

I~~~~~~~~~~*

I~ u'

IY".

I4 gd'1

3 iuel*Lctono avstadcnto ie i euor ony
Por~out Carolina.

I~~~~~~~~~~~~~~~~~~~~~~I'

WINCH

� . I
I ~~~~~~~~~~~~~~CYLINDER

PRESSURE
CONTROL
I /d .'11VALVE
.I I'HA~yESTI
L.-, .HEA..

*~~

Figure 2. The Clemson mechanical oyster harvester prototype, showing
configuration of the harvester head and the head control system.

/.8J-

i~~~~~~~~~~~~ .
(I,

H"W r 6.,
I

I 8'
4..

I NN n::

a..

~bJ r.,II ____
I ..
c4ROWL C --
1- 4'-

I ~~~~~~~~3~~..
e..

I _I I I _
Figure 3. Total number of encrusting and non-motile species collected at each
Ct- strata for each sampling period.

ANIPq6ARIU a I. MMflIA1

31D ~ ~ ~ ~ ~ ~~

ls -aw I0 ~I

800-~-h::r@i*

*~~~~pce d-it7 Or Mo il an no-ooil ivreats 7.ose im

fo ie .65 4qSA't tkUfrmhghadlw itria tataambt
ha~s n otrlstsfreahsmln ero 'ero'spoutmmn
~~~~~creaiocofien. (rw

U 200- UNner ismpressa
MTATA oao
5 HARVEST:

IbNig# Imrlltdal
2000- CNTtR0L;
t=#iqn Im"midos

- AL' Iatmntdc

3200-

to-
$1rehleio J1eme id P
4-' p

Pit- M= SPRING SUMME FAL WINTER
� �.tnp. henedleff
O

IA aT_

Figure 5. Total number of individuals of the numerically dominant species collected
Figure 5. Total number of individuals of the numerically dominant species collected
in pooled replicate samples from each stratum/kite during each sampling period.

Appendix A. Salinity (�/oo) and temperature (OC) readings at both harvest
and control sites for all sampling periods.

Salinity (0/oo) Temperature (�C)
Harvest Control Harvest Control

Preharvest 16.0 14.0 18.0 16.9

Immediate
Post-Harvest 13.0 12.0 15.8 14.0

Spring 14.0 14.0 21.0 19.4

Summer 22.0 22.0 30.6 31.8

Fall 28.0 29.0 21.6 20.5

Winter 20.0 20.0 10.8 8.7