Tidal marshes the boundary between land and ocean

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

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RMI,, 1980
1"dal a es
The Boundar Between Land and Ocean

ish and Wildlife Service
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1 0** 1 U.S. Department of the Interior

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FWS/OBS-80/15
JULY 1980

The Biological Services Program was established within the U.S. Fish and Wildlife Tidal Marshes-The Boundary
Service to supply scientific information and methodologies on key environmental issues Between Land and Ocean
that impact fish and wildlife resources and their supporting ecosystems. The mission of
the program is as follows: By James Gosselink
� To strengthen the Fish and Wildlife Service in its role as a primary source of Center for Wetland Resources
information on national fish and wildlife resources, particularly in respect to Louisiana State University
environmental impact assessment. Baton Rouge, Louisiana 70803
� To gather, analyze,'@nd present information that will aid decisionmakers in the Illustrations by:
identification and resolution of problems associated with major changes in land Bobbie Young
and water use. Diane Baker
� To provide better ecological information and evaluation for Department of the Center for Wetland Resources
Interior development programs, such as those relating to energy development. Louisiana State University
Information developed by the Biological Service Program is intended for use in the Project Officer:
planning and decisionmaking process to prevent or minimize the impact of development Elaine W. Bunce
on fish and wildlife. Research activities and technical assistance services are based on an National Coastal Ecosystems Team
analysis of the issues,a determination of the decisionmakers involved and their informa- U.S. Fish and Wildlife Service
tion needs, and an evaluation of the state of the art to identify information gaps and to
determine priorities. This is a strategy that will ensure that the products produced and Published by:
disseminated are timely and useful. U.S. Fish and Wildlife Service
Projects have been initiated in the following areas: coal extraction and conversion; Biological Services Program
power plants; geothermal, mineral and oil shale development; water resource analysis Questions or requests for this publication should be addressed to:
including stream alterations and western water allocation; coastal ecosystems and Outer,
Continental Shelf development; and systems inventory, including National Wetland Information Transfer Specialist
Inventory, habitat classification and analysis, and information transfer. National Coastal Ecosystems Team
U.S. Fish and Wildlife Service
The Biological Services Program consists of the Office of Biological Services in NASX-Slidell Computer Complex
Washington, D.C., which is responsible foroverall planning and management; National 1010 Gause Blvd.
Teams, which provide the Program's central scientific and technical expertise and Slidell, Louisiana 70458
arrange for contracting biological services studies with states, universities, consulting DEPARTMENT OF THE INT ERIOR FZi;o7e
firms, and others; Regional Staff, who provide a link to problems at the operating level; U.S. FISH AND VIIIDLIFE SERVICE
and staff at certain Fish and Wildlife Service research facilities, who conduct inhouse
research studies.

%0 C-d'
Property of CSC Librazy

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

most fertile agricultural land (as much rate of about one-half percent per
as 5 tons per acre annually). This year . One million acres of coastal
high productivity occurs because tidal marsh have been lost since 1954, as
marshes are the boundary or "inter- documented by high altitude aerial
face" between the ocean and the adja- photography of the coast. 2 By the
cent land. Interfaces in general are year 2000, if the present rate of marsh
Introduction sites of unusual activity and tidal loss continues an additional one mil-
marshes are no exception. They re- lion acres @ill have disappeared.
ceive fresh water, sediment, and nu- Public consciousness, combined with
Tidal marshes of the United States trients from the land and are also ex- legislation at the State and National
cover about 13,000 square miles, ap- posed to salty oceanic waters that add levels, has begun to reduce the rate
proximately the combined area of Con- additional nutrients. As a result, of marsh loss from urban, agricultural
necticut and Massachusetts. From a grasses grow tall along the boundary and industrial development. But other
global perspective, marshes form a nar- between tidal streams and marshes, more subtle activities that still occur
row fringe of intertidal flats along becoming shorter and sparser as one in coastal wetlands and in areas up-
ocean coasts. They are vegetated by moves inland. The abundance of food stream may, in the long run, produce
a few hardy species, mostly grasses, and shelter along this marsh edge re- changes just as important.
that have been able to adapt to the sults in a concentration of animals, The relationship between these
unusual stresses of tidal flooding and from tiny invertebrates to game fish activities and wetland alteration is
salt water. 1 Tidal marshes provide and fish-eating birds. (See center often unexpected. For example, con-
feeding and nursery grounds for many plate) The stems of individual grass tinual sediment deposition is necessary
commercially important fin- and shell- plants, bathed daily by salty water, to maintain tidal marshes. Flood con-
fish. Sport fishermen, as well as are coated with a dense layer of mi- trol levees on ',the Mississippi River
hunters, are attracted to these areas croscopic animals, one-celled algae, eliminate most of the sediment flow into
by the plentiful supply of fish, water- and bacteria that provide food for adjacent marshes, resulting in a net
fowl, and furbearers. The value of small animals. Thus, at all levels the wetland loss of about 10,000 acres per
cno tidal marshes has been recognized by interactions between land and flooding year. Blockage of normal sediment
c?Q the passage of Presidential Executive water contribute to the high produc- supplies to the coast by the Toledo
q:T_ Order (E.O. 11990) in 1977, prompting tivity and value of salt marshes. Bend Dam on the Sabine River (bor-
State and Federal agencies to minimize dering Louisiana and Texas) has ac-
impacts or alterations in wetlands. celerated marsh loss and changed the
The purpose of this brochure is to seasonal freshwater flow enough to re-
provide an overview of the ecology of duce shrimp migration into the estuary.
tidal marshes along the Gulf coast of Human Impact Oil-well access channels and pipeline
the United States factors affecting canals, criss-crossing the deep draft
them, and their vai@e. navigation waterway in the Calcasieu
Productivity of tidal marshes is In the United States, coastal basin of Louisiana, have linked the
4-
coWparable to, or exceeds, that of our marshes have been disappearing at a Gulf of Mexico to freshwater marshes.
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Figure 1. Two-thirds of the human population live on one-third of the world's land area adjacent to ocean coasts. Wetlands are drained for agriculture, housing, and
industry. Man alters flooding patterns by constructing road embankments, canals with elevated spoil banks, and levees along streams. Ecological relationships are altered
when man pollutes estuarine streams and lakes with sewage, fertilizers, and pesticides.

Salt water, has moved inland, killing load is deposited, The sediments build
vegetation whose roots prevent soil up until they reach the water surface,
erosion. Consequently, wetland vege- at the same time building out into the
tation has changed and erosion rates Gulf in a fan-shaped delta. The per-
have increased. Toxins and nutrients Origin s of iodically exposed mud flats are slowly
in wastewater from urban and indus- colonized by freshwater marsh plants
trial sources have drained into the up- Ti'dal Marshes because river water keeps the salinity
land end of these canal complexes. low. The river continues to extend its
Instead of filtering across wetlands, course into the Gulf until it breaks
they now enter directly into coastal through its natural levee upstream and
lakes, polluting the water and, in ex- From a geologic perspective, finds a shorter route to the sea. As
treme cases, causing fish kills.3 marshes are short-lived features of the with any shortcut, this brdach soon
These impacts have a common ori- coastal landscape. Compared to rocky becomes the preferred channel and,
gin. The development was undertaken headlands, such as those found on the over the years, the path of the old
for some worthwhile cause unrelated to north Atlantic and the Pacific coasts, river is abandoned. The mouth of the
wetlands. Individually most were small which may be millions of years old, new channel becomes the site of a new
projects compared to the larger unfore- most of the tidal marshes of the United delta. As river flow decreases in the
seen consequences on the tidal marshes. States have a life span measured in old channel, the old marsh enters a
Man's activities redirect the enormous thousands of years. destructional phase; salt water in-
powers of nature, as a valve switches The energy of ocean currents and vades, salinity levels increase, and
a flow of water. A chain of related storms moves marine sediments- -sands, salt-tolerant plant species replace the
events often follows. The examples muds, and clays--along the coast freshwater plants that once occupied
are many. A small dredged channel where they are deposited in shallow the area (Figure 2).
becomes a major short cut for water water. Gradually, the bottom is ele- At any time, the elevation of the
flow, with the result that natural me- vated, extending the intertidal zone marsh surface is a balance between
andering channels are abandoned and and building sandy barrier islands land building upward from sediment
filled with silt. Dredged materials de- which parallel the coast to enclose deposition, and land subsiding from
posited along canals block water flow shallow bays. Marsh grasses gradually consolidation of marsh sediments and
to thousands of acres of wetlands, colonize the fringing mudflats, stabiliz- from sinking of the land mass under
which can no longer function as nur- ing the surface, spreading slowly out- its own weight. In the initial growth
sery grounds. Pesticides and herbi- ward into the bay, and fixing the phase deposition predominates. After
cides, carried in nearly undetectable course of the tidal streams that mean- the river shifts its course, fewer sedi-
concentrations from farm lands in run- der through them.4 These building ments enter the marsh and land subsi-
off water, are concentrated by birds processes are typical of marshes of dence exceeds sediment deposition.
such as brown pelicans, peregrine fal- the south Atlantic coast of the U.S. Along the Gulf coast, subsidence rates
cons, bald eagles, and ospreys, caus- and of the eastern and western Gulf of are as much as 1 centimeter per year,
ing sterility or fragile egg shells which Mexico. and in many areas sediment deposition
break during incubation. In contrast, the other tidal marsh is much less. As marsh elevation de-
The tidal marsh is threatened by systems of the United States are built clines, the grasses die and the marsh
the concentrated development of human by rivers carrying sediments into shal- reverts to a shallow saline lake or bay.
society along our coasts (Figure 1). low coastal waters. The Mississippi Historically, this cycle takes about one
Its future existence depends heavily River delta is one of the best examples thousand years.' Since man has occu-
on widespread understanding of the of this kind of marsh development. pied the coastal zone, however, the
value to man of this natural ecosystem, This river system has built 40% of our cycle has accelerated. Man-made lev-
and on a broader appreciation of the Nation's coastal wetlands.5 As the ees prevent spring floods from carry-
strong ties between the marsh system Mississippi River flows into the Gulf of ing silt into the coastal marshes. As a
and its neighbors, the uplands and the Mexico, its waters spread out, cur- result, nearly all of the marshes built
ocean. rents slow, and much of the sediment by the Mississippi River along the cen-

tral coast of the Gulf of Mexico are in A. New Stream Channel Forms
a destructional stage.
Plans to divert river water into Natural Levee
Louisiana's coastal marshes hold poten-
V,
tial for slowing the rate of wetland
loss, but the newly forming delta of
the Atchafalaya River is the only site
of significant wetland growth along the
northern Gulf coast.

Subsurface Deposits
Of River Sediments
Marsh Ecosystem
The physical characteristics of a B. Marshes Build Out From The Channel
tidal marsh are determined by sedi- Natural Levee
ments carried in and deposited by
rivers or wind-driven coastal waters, Marsh Pests z-; " _@soz,
rainfall and the timing of the spring
thaw five hundred miles upstream, and
severe tropical storms originating Subsurface
thousands of miles away in the Atlantic River Deposits
Ocean. Many outside forces also de-
termine the biological characteristics of
a marsh. Considering the variation in
these outside forces, it is surprising
that there is great similarity in the
marsh species found all the way from New Distributary Channel
Resulting From
the Gulf coast to the northern border C. Channel Abandoned Stream Diversion
of the United States. The dominant Abandoned Channel
plants in all of these marshes are two
grasses. Saltmarsh cordgrass (qpar-
tina alterniflora) is found in true
tidal marshes. In marshes of slightly Marsh Pests
higher elevation Spartina patens,
called salt meadow hay or salt meadow
cordgrass, occurs. Also widespread Subsurface 4
are salt grass (Distichlis spicata) and River Deposi - Clav
black rush (Juncus roemerianus).
Saltmarsh plants have adapted to two
stresses foreign to most land plants--a Mixed Marine And
saturated root zone depleted of oxy- River Deposits
gen, and a high salt concentration that Figure 2. On the Gulf coast of the United States marshes formed by river sediments typically have a 1000-year
literally dries out the tissues of most cycle of growth and decay. (A) New freshwater marshes form where a river channel empties into a shallow sea,
plants. Perhaps the inability of other depositing sediments and forming mud flats. (B) These flats spread, and are colonized by marsh plants. (C) When
plants to adapt to these stresses has the river abandons that channel, ocean forces begin to dominate. The marshes become salty and salt-adapted
left the marsh zone free to these salt- plants invade. Slowly the marsh sinks as sediments compact. The area reverts to a shallow open sea.

tolerant species - Within a marsh, these wastes from the marsh along with areas of strong tidal currents, there is
subtle differences in the degree of dead plant litter and the dissolved or- some evidence that larvae and juveniles
adaptation by plants often result in ganic material that gives the water its ride with currents which carry them
well-defined boundaries between plant dark coloring. The activities of marsh into the marsh, but move down into
communities. These boundaries are animals are adjusted to this cycle. the bottom muds to escape ebbing
defined by slightly different combina- Fiddler crabs are active at low tide tides. While in the marshes, the
tions of elevation, soil characteristics, and inactive at high tide. Oysters in feeding activity of these small organ-
salt concentration and inundation fre- the intertidal zone open their valves isms is synchronized to both the tides
quency. widest to feed during high tides. and the day-night cycle. High water
Marshes and adjacent tidal creeks Oysters and fiddler crabs are not enables the juvenile shrimp to move
along the Atlantic and Gulf coasts are the only marsh animals to 'respond to into and feed in flooded marshes and
also inhabited by similar species of the sun and the moon. Microscopic shallow marsh ponds. Feeding occurs
animals . Fiddler crabs, periwinkle single-celled diatoms, living near the primarily at night when hungry preda-
snails, grass shrimp, silverside and surface of the marsh mud, time their tors are relatively easy to avoid.
mud minnows, clapper rails and red- vertical migrations of fractions of an Emigrating shrimp swim f rom bottom
winged blackbirds are common resi- inch to move up into the light during muds into the water column to move
dents of all tidal marshes. Even the the day, and down into the sediments passively with ebb tides, principally at
migrating members of the community-- at night. The same is true for many night. The largest migrations coincide
shrimp, menhaden, flounder, ancho- tiny aquatic animals which move up with the strongest tides that occur
vies, mullet, wading birds and water- and down in the water column in re- every 28 days when the moon and the
fowl--are the same or closely related sponse to light. sun are in line with the earth.
species from north to south. Climatic These cycles are not just inter- This part of the tidal marsh story
differences, for example, rainfall, tem- esting phenomena to be cataloged by would be incomplete without mention of
perature extremes, and sunlight, seem scientists and made the subject of tele- the ducks, coots, and geese, whose
to take a back seat to flooding and vision documentaries. The future of annual migrations are regulated by the
salt stress, determining not so much nearly all of our coastal fisheries de- relative lengths of the day and night.
the kinds of plants and animals that pends on our appreciation of complex They move annually from Alaskan and
inhabit the marsh, as the length of the interactions of daily, monthly, and Canadian breeding grounds across
growing season and therefore its pro- seasonal cycles that program the thousands of miles of land to winter in
ductivity. movements of virtually every major marshes along the Gulf coast. Gener-
Perhaps the most interesting coastal fishery species. The details ally, these groups of birds prefer
forces that shape a marsh are the two and timing vary from species to freshwater marshes, but the lesser
cyclic ones, the annual cycle of the species, but the pattern is similar to snow goose and numerous species of
seasons determined by the orientation that of the brown shrimp (Figure 3).1 dabbling and diving ducks are com-'
of the earth to the sun, and the tidal Generally these species spawn offshore monly found in tidal marshes, espe-
cycles controlled by the orbit of the in the ocean. The floating larvae, too cially in low salinity brackish
moon around the earth. On the Gulf small to swim far under their own marshes.3
coast, tides flood and ebb once every power, are carried passively by ocean
24 hours 50 minutes, while on the At- currents through tidal passes into
lantic and Pacific coasts tides occur coastal estuaries. They move into
twice during that period. This regu- fringing tidal marsh-pond complexes
lar pulse is like breathing for an ani- where the shelter of the marsh and the Marsh Food
mal. Falling waters expose marsh soils abundant food supply provide a secure
to air, replenishing the oxygen needed nursery ground. As juvenile shrimp
by nearly all living organisms. Rising approach maturity, they return to the Chain
tides carry in sediments and nutrients ocean to complete their life cycle.
necessary for plant growth, and flush Scientists have only begun to under-
from the sediments accumulated meta- stand the cues that enable an animal to Tidal marsh zones have been
bolic wastes. Receding waters carry follow this complex route. Once into called nursery grounds because of

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Salt grasi;,
Sattmeadow bay

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Salt grass

Saltmeadow hay

Gulf killitish
PIWI@Ir rab
Bay -anchovy

Tidewater silverside
Widgoon grass

Hermit crab

Grass shrimp

Black rush

The edge of a tidal marsh is an area of concentrated activity for many organisms. The rich nutrients in the water stimulate plant growth. The resulting food and shelter attract many sma
enlarged at varying scales to show details.

Snow geese . . . . . .

arsh hawk

Saltmarsh cordgrass 'V

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Marsh periwinkle

Blue crab

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Amphipod
Polychaete Brown shrim
Saltmarsh cordgrass Southern flounder
Ribbed mussel

animals, which in turr. draw predators looking for an easy meal. This drawing depicts typical plants and animals in the fall season in marshes along the Gulfcoast of the United States,

their invasion by young marine fish fy sewage water. So efficient is this giving a golden sheen to the soft mud
and shellfish. The term is appropriate natural system for growing grass that, surface.
because the long sinuous marsh-bayout on a per acre basis, each year's pro- These groups of plants together
edges provide secure shelter and food duction is as great as on our most in- produce very high levels of organic
is abundant - But tidal marshes are tensively cultivated farm land. 8 matter in tidal marsh systems. How-
much more than nurseries. On the Were marsh grasses the only ever, it is not at all obvious how the
Gulf coast, these marshes support high source of food for aquatic consumers, living marsh grasses are used by ani-
concentrations of overwintering water- the estuarine ecosystem would not be mals. Although there is evidence that
fowl; year in and year out they pro- as productive as it is. But other ducks and geese feed directly on
duce large yields of nutria and musk- plants (planktonic algae, sea grasses, marsh plants, these animals are often
rat, and fish and shellfish. This and benthic algae) flourish in the quite selective, eating the seed clus-
large production of animals is possible waters adjacent to the marshes, and it ters only, or the underground tubers
for two reasons: the high level of is the combined productivity of all of relatively uncommon species such as
plant growth and the simple food these groups that accounts for t ihe im- three-cornered grass. The dominant
chains of the marsh ecosystem. Both portance of the marsh-bay system. In grasses escape unscathed. These
of these, in turn, result from the po- aquatic systems, the food chain starts grasses also escape direct grazing by
sition of the tidal marsh between the with one-celled microscopic floating estuarine fish and shellfish. Thus the
land and the ocean. plants- -phytoplanktonic algae--which role of marsh grass in the food chain
Consider plant growth first. All grow and multiply in the dilute nu- was for many years problematic. Since
living animals, man -included, derive trient broth of sunlit surface waters. the early 1950s, evidence has accumu-
food ultimately from plants which man- These algae form the base of a grazing lated that marsh grass contributes sig-
ufacture organic materials from water, food web because they are cropped di- nificantly to aquatic productivity after
carbon dioxide and a few minerals. rectly by minute floating animals called it dies. The decaying marsh grass
Sunlight provides the energy for this zooplankton; by fishes such as the bay and resulting dissolved organic ma-
process, called photosynthesis. Man anchovy and menhaden; by clams; and terial are flushed from the marsh by
uses fossil energy sources to boost his by oysters, which strain water tides and storms, becoming available to
food production, that is, to fuel trac- through their gills to concentrate the aquatic consumers indirectly.*
tors, to manufacture fertilizers, and to algae before ingesting them. Phyto- It is difficult to quantify the rel-
process foods. In the same way, the plankton production is especially high ative importance of each of the sources
plant production of the marsh system in estuarine systems, because of high of organic food, but ecologists in Lou-
is subsidized by the energy of tides nutrient concentrations. isiana have estimated that phytoplank-
and of rivers which continuously re- ton, bottom-dwelling plants and marsh
plenish the nutrients marsh plants re- The other aquatic plant group grass each provide equivalent amounts
quire for growth. Rainfall far up- that supplements phytoplankton pro- of organic material to the estuarine
stream washes fertile soil off the land, duction is composed of sea grasses and food chain (Figure 4) 9 In other
especially farm land, into streams benthic algae that can grow on the bay marsh-estuarine systems where open
where it is eventually carried to the bottom because sunlight penetrates water areas are large compared to
coast. As silt-laden river water tra- through the shallow water. The im- fringing marshes, phytoplankton pro-
verses an estuary, the rhythmic tidal portance of this plant community varies ductivity predominates, with dead
pulses push the water over adjacent with the type of substrate and the plant material from upstream an impor-
marshes where the dissolved nutrients depth and clarity of the water. Where tant food source only when river in-
and the nutrients attached to fine soil sediments are relatively stable and the flow is significant.10
particles become available to stimulate water clear, sea grasses may abound In addition to the diversity of
the growth of plants. Marshes are as they do along the eastern coast of
such effective nutrient traps that they the Gulf of Mexico. In turbid waters, *Kn-other, probably minor, pathway of
are being used in some places to puri- low light intensity and smothering sed- food energy flow from marsh to
iments often prevent sea grass growth. water is through minnows and small
TA term used in South Louisiana to In these situations, bottom- dwelling, shellfish feeding in the marsh during
mean a tidal stream. single-celled diatoms often flourish, high tides.

plant producers and their high levels rule of thumb, 1000 calories of plant grazes phytoplankton directly, a one
of productivity, the simple estuarine organic energy will support only about step food chain.
food chains are a second reason for 100 calories of a grazer (an animal Many other animals depend on a
the high yield of commercial species. which eats plants), 10 calories of a 11detritus" food chain in which sea
Animals use energy not only to grow, carnivore (an animal which eats other grasses and marsh grasses are the raw
but also to move about in search of animals), and 1 calorie of a top carni- materials. The term detritus comes
food, to digest what they eat, to avoid vore (an animal at the top of the food from a Latin word meaning "worn
predators, and to counteract changes chain). As a consequence, short sim- down" or "disintegrated." As used by
in water temperature and salt concen- ple food chains produce much more ecologists, it refers to the decaying
tration. No energy conversion is one harvestable food than do long complex remains of plants and animals. A de-
hundred percent efficient and some ones. In tidal marsh systems, the tritus food chain is one in which
energy is lost as it is transferred up menhaden, the most abundant com- plants are not grazed while alive, but
each step in the food chain. As a mercial fish species of the Gulf coast, are used af ter they die. The decom-

Eariy Fay
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Summer

Winter

Spring

-tany
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Figure 3. The brown shrimp is typical of many marine animals that spawn offshore, move into the estuary as juveniles, and emigrate to sea again as adults. Their sojourn
in the estuary corresponds with the time of peak food production from the adjoining marshes.

Marsh
grasses

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Top carnivores
CC$
CO 0 -0 4sea trout
V ankton Sou hern
Phytopl I
t flounder
Menhaden

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ankton
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E 0 CO and detritus
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'6 o eaters Bay anchovy
CL
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=3
CY Mid - carnivores
N Killifish
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Spot
CL W t
W Sea catfish
A Detritu
Tidewater silverside
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and bottorn-
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Figure 4. The food that marsh and estuarine animals depend on comes from three sources: floating single celled algae (phytoplankton), sea grasses and benthic algae, and
marsh grasses swept into the adjacent water. Certain animals prefer each of these plant food sources, while other carnivorous fish and birds eat only other animals. In this very
Ae.

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simplified illustration of marsh-estuary food chains ofa Louisiana salt marsh, the bar graph illustrates the annual production of each group of organisms. (Multiplying each
number by 10 approximates the production in pounds per acre.) The heights of the bars decrease dramatically as the animals feed further and further from the plant
food base.

posing remains are eaten by scaveng-
ing animals, which are in turn eaten
by carnivores as in a grazing food
Attacked, colonized chain. Three differences distinguish
and eaten by Detritus- the "detritus" food chain from the
grazing food chain. First, bacteria
bacteria a mixture
Plants of bacteria
play an important role, breaking down
shredded by small and dead the cellulose* in grasses, which is in-
crustaceans and
plant digestible to animals, to a usable chem-
snails "V remains
ical form. Without exception, higher
animals do not manufacture the neces-
sary enzymes to accomplish this. Even
t depend on the bacteria in
a cow mus
its rumen (stomach) to break down the
m grass it eats. The detrital system of
the salt marsh performs exactly the
same function in the water where
broken bits of plant material wash
back and forth with the tide. It is a
kind of external rumen, and its pro-
ducts support a major marsh-estuarine
Death food chain. Second, because nearly
all of this decomposition occurs on or
Raw plant food Shrimp, crabs, in the bottom sediments, the scaveng-
enters the (b and small crustaceans ing animals are predominantly bottom-
detrital mill dwellers (for example, very small
wormlike nematodes and crustacean am-
-feeding
phipods and isopods) or bottom
ants-:
Marsh pi fish and shellfish - These animals
ingest the decaying plant-bacteria ma-
terial . strip from it and assimilate the
Feces,
bacteria, and egest the remains in
neatly packaged fecal pellets that can
be colonized again by bacteria (Figure
5). Finally, tides and storms are im-
p
ortant in the estuarine detritus food
chain. They aid in breaking up the
plants and flushing the detritus out of
ejeGOL"O@\
the marsh into the shallow estuarine
Assimilated food
leaves detrital mill waters where it becomes available to
aquatic animals.
as animal tissue
Like the grazing food chain, the
detritai pathway is also efficient. Bac-
teria have been shown to incorporate
dead grass into their cells with an ef-
Figure 5. Marsh grasses feed the detrital mifl. Small marsh animals physically shred the dead grass, enabling ficiency greater than 20%; and shrimp,
bacteria to invade it and break it down chernically, so that animals can assimilate it and grow. Their waste *A fibrous substance making up the
products are recolonized by bacteria and the cycle is repeated. cell walls of plants.

the most valuable Gulf fishery species, Gulf coast marshes during the winter lars generated from the living re-
feed directly on the resulting detrital create a hunter's paradise, and fur- sources of his land. On the Gulf
material. The most valuable fishery bearing muskrats are regularly trapped coast he may lease his wetland for
species on the Gulf coast all have in brackish marshes. Harder to quan- trapping and for duck hunting for
short food chains, feeding directly on tify are other free services provided about $10 an acre a year. In con-
plants or on plant detritus. by wetlands. When marshes are trast, in a recent study of Louisiana
flooded by tidal waters, the vegetation wetlands the annual value of an acre
traps sediments which might otherwise of coastal marsh for commercial fishing
block navigation channels and harbors. was estimated at $94, for commercial
For example, when the great marshes trapping $3.47, and for sport fishing
Value of of the southeastern coast of England $12-13 The wetlands along Lake Mich-
were first diked and filled in the 19th igan are estimated to have an annual
century, all the natural harbors silted value of $31 per acre for waterfowl
Tidal Marshes in. As a result, constant dredging at hunting. 14 The protection marshes
a considerable cost to the public be- afford inland urban areas against
came necessary to keep the harbors storms and their water-cleansing
Marshes are economically valuable operational. 12 Wetlands also buffer action save the public thousands of
for fisheries far beyond the number of inland areas from the damaging effects dollars per acre annually." Thus,
fishes that are caught directly in adja- of severe storms, acting as huge water the value of the marsh in its natural
cent tidal streams. Most of the impor- reservoirs that reduce flooding in sur- condition is small indeed to the owner,
tant coastal fishery species of the rounding uplands. compared to its value to the general
United States must have access to es- Even more difficult to quantify public. The wetland property owner's
tuaries and marshes during some phase are the aesthetic values of wetlands. economic incentive to drain and de-
of their life history. Recent research Conversations with coastal residents, velop private acreage conflicts directly
has revealed how important this aspect hunters, and sport fishermen usually with the public's interest in maintain-
of the marsh is: shrimp catches in reveal a deep appreciation for the ing the benefits of a natural marsh.
beauty of wetlands. Our inability to This conflict will intensify as popula-
fisheries around the world are directly
related to the area of marsh in the put a dollar value on this kind of ex- tions along our coasts expand andl
shrimp nursery grounds, not to the perience does not make it any less real pressures to develop natural areas in-
area of estuarine or offshore coastal or less important. crease. A public informed of and in-
waters where they are caught." The diversity of these values terested in the functions and values of
Protecting fisheries is not the leads to a serious problem in attempts coastal wetlands is the best safeguard
only economic reason for conserving to preserve wetlands; the private to insure reasonable protection of our
wetlands. The waterfowl that crowd owner of a marsh seldom sees the dol- wetland heritage. 16

NOTES ON Tidal Marshes-The Fish and Wildlife Service, Office of Biological Services. "Turner, R. E. 1977. Intertidal vegetation and com-
FWS/OBS-78/9 through 78/11. mercial yields of penaeid shrimp. Trans. Am. Fish. Soc.
Boundary Between Land and Ocean 'Miller, W. R., and F. E. Egler. 1950. Vegetation of the 106: 411-416.
Wequetequock-Pawcatuck tidal marshes, Connecticut. 12 Coates, D. R., ed. 1972. Environmental geomorphol-
Ecol. Monogr. 20: 144-172. ogy and landscape conservation. Vol. 1. Benchmark Pap-
sTurner, R. E., and J. G. Gosselink. 1975. A note on ers in Geology. Dowden, Hutchinson and Rose,
standing crops of Spartina allerniflora in Texas and Stroudsburg, PA.
Florida. Contrib. Mar. Sci. 19:113-118. 13Mumphrey, A. J., J. S. Brooks, T. D. Fox, C. B.
6Frazier, D. 1967. Recent deltaic deposits of the Missis- Fromherz, F. J. Marak, and J. D. Wilkinson. 1978. The
sippi River, their development and chronology. Trans. value of wetlands in the Barataria Basin, Louisiana. Dept.
'This brochure describes estuarine intertidal emergent Gulf Coast Assoc. Geol. Soc. 17:278-315. of Transportation and Development Coastal Resources
wetlands, which are technically "lands transitional be- 7Condrey, R. E. 1979. Draft environmental impact Program, Baton Rouge, LA. 151 pp.
tween terrestrial and aquatic systems where the water table statement and fishery management plan for the shrimp 14jaworski, E., and C. N. Raphael. 1978. Fish, wildlife,
is usually at or near the surface ... characterized by erect, fishery of the Gulf of Mexico, United States waters. Gulf of and recreational values of Michigan's coastal wetlands.
rooted, herbaceous hydrophytes." Cowardin, L. M., V. Mexico Fishery Management Council, Tampa, FL. 220 pp. Michigan Dept. of Natural Resources, Lansing. 98 pp.
Carter, F. C. Golet, and E. T. LaRoe. 1979. Classification RTeal, J. M., and M. Teal. 1%9. Life and death of the I sGosselink, J. G., E. P. Odum, and R. M. Pope. 1974.
of wetlands and deepwater habitats of the United States. salt marsh. Little, Brown and Co., Boston, MA. 278 pp. The value of the tidal marsh. Louisiana State University
Office of Biological Services, Fish and Wildlife Service, 911opkinson, C. S., J. W. Day, Jr., and B. T. Gael. Center for Welland Resources, Baton Rouge. Sea Grant
U.S. Dept. of Interior. FWSIOBS-79131. In this report 1978. Respiration studies in a Louisiana salt marsh. An. Publ. No. LSU-SG-74-03.
marshes are defined as including vegetated wetlands along Centro. Cienc. del Mar Y Linmol. Univ. Nal. Aut6n.
with adjacent streams and small lakes. Mexico 5(l):225-238. 16Recommended general references on tidal marshes
'Gosselink, J. G., and R. H. Baumann. 1980. Wetland I ONixon, S. W. 1980. Between coastal marshes and coas- are: Teal, J. M., and M. Teal (see note 8 above); Niering,
inventories: wetland loss along the United States coast. tal waters-a review of twenty years of speculation and W. A. 1966. The life of the marsh. McGraw-Hill Book Co.,
Zeitschrift fur Geomorphologie 34:173-187. research on the role of salt marshes in estuarine productiv- New York. 232 pp; Horwitz, E. L. 1978. Our Nation's
'Gosselink, J. G., C. L. Cordes, and J. W. Parsons. ity and water chemistry in P. Hamilton and K. Mcdonaid, wetlands. Interagency Task Force Report, Coordinated
1979. An ecological characterization study of the Chenier eds. Estuarine and wetlands processes. Plenum Press. New by Council on Environmental Quality. U.S. Government
Plain coastal ecosystem of Louisiana and Texas. 3 vol. U.S. York (in press). Printing Office, Washington, D.C. 70 pp.

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