    [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
                                                 M@ rsh

        1 0** 1         U.S.      Department of                 the Interior

                                                                                                                                                         wA,             A@N

                                                                                                                                                                                                      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.

                                                                                                     2

                 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-

                                                                                      3

                   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.

                                                                                                       4

                    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

                                                                                                    5

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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                     . . . . . .

                                                                                                                                                                                                                                 4,

                                                                                                                         arsh hawk

                                                                                    Saltmarsh cordgrass                                                                                                                                  'V

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                                                                          Ilk

                                                                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.

                                                                                        8

                       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
                                                         r(

                                     Summer

                                                                               Winter

                                  Spring

                                                                                                   -tany
                                                                                                                                                                       q

                                                                                                                                                   %
                                                                                                                                 Pell,

                                                                                                                                           A
                                                                                                                                                POPOV
                                                                                                                                              *

                                                                                                                                                          @w

                       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.

                                                                                                          9

                    Marsh
                    grasses

                                 0
                                                                                                                                                                .. 7..
                                                                               W   42
                                                                              \7  C2
                                 CU
                                                                                                                                                                  Top carnivores
                    CC$
                                 CO                            0                                                       -0                                       4sea trout
                                                          V                         ankton                                                                        Sou hern
                                                                           Phytopl                                     I
                                                                                                                                                                     t    flounder
                                                                                                                             Menhaden

                    0.
                                                      C?                                          zo6p,
                                                                                                         ankton
                                                      0
                                               0                                                                         Herbivores
                    E            0             CO                                                                        and detritus
                                 -             CO
                                 '6     o                                                                                eaters                Bay anchovy
                                                      CL
                                 CO     C\1
                    =3
                    CY                                                                                                                                             Mid - carnivores
                                                      N                                                                                                            Killifish
                                        0      '6
                    CD                         C)                                                                                                                  A lanlic croaker
                                                                                                                                                                   Spot
                    CL           W                                                                                                                                   t
                                               W                                                                                                                   Sea catfish
                                                                      A                       Detritu
                                                                                                                                                                   Tidewater silverside
                    E            W             as
                    03           (D     0      0)     0)               1
                                                                                   Sea grasses                                   Shrimp
                          0             a-     0)     -      -                                                         I
                                                                                  and bottorn-
                                               CO            U)
                          7                                                       dwelling algae
                                                             0
                                                                              (eol                                                                    pshead
                    =3
                                                                                                                                                  min  w
                    0                                 0
                    IL                                       Cz      W         tip
                                                                     C:L
                                                      W
                          CU
                                                      3:
                                                                                                                                             -Blue Cnw@
                                            Group

                 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.

                                                               Ak,

                                                                                                     S
                                                                                                         P

                                                                                                                                                    ee
                                                                                                                                                <!-'i'nn.'w-hed

                 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.

                                                                                                       10

                                                                                                                                                           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

                                                                                         12

                          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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