Estuaries and Salt Marshes Part 2

  SALT MARSHES (tidal marshes)
I. Definitions and Characterization

"Salt marshes are communities of emergent herbs, grasses, or low shrubs rooted in soils that are alternately inundated and drained by tidal action"
II. Environmental Characteristics
    A. More intense variations in salinity and temperature than in the estuary itself
    B. Intertidal
    C. Organisms there are halophytes – grow in high salt content sediments
    D. Anoxic soils
III. Types of Organisms
    A. Plants -- depauperate in species (harsh environment);
            mostly herbaceous angiosperms (Spartina - cordgrass, Juncus - rush, Salicornia)
    B. Animals
        1. marine – crabs, mussels, snails, amphipods, shrimp, fishes
        2. terrestrial – insects, raccoons, birds
    C. Wide distribution of these few species
IV. Zonation
    A. Can seem to be broad, flat, monotonous expanses; are cut by tidal creeks
    B. Salt marshes start with colonization of muddy areas by Spartina alterniflora (smooth cordgrass) that propagates vegetatively.
        Slows the waves; increases sedimentation; results in creation of a ‘high marsh’ where other plants can colonize
    C. Zonation from sea
        1. New England
            Spartina alterniflora ->  salt marsh hay (Spartina patens)  -> rush (Juncus) -> marsh elder (Iva frutescens)
        2. Southern
            Spartina alterniflora ->  salt marsh hay (Spartina patens) ->  salt pans -> rush (Juncus)

            high temperatures and evaporation lead to the salt pans (can be 100 psu) –
                    areas without plants, surrounded by salt meadows
        3. West coast
            Spartina alterniflora ->  Salicornia

    D. Causes of Zonation
        1. unlike the rocky intertidal, in the salt marsh competition often determines the
                upper boundary and physical tolerances set the lower boundary
            a. Competitive dominance sets upper limits
            b. Salinity tolerances set the lower limits
            c. Experimental evidence
 
        2. mutualisms –
            a. Spartina alterniflora and fiddler crabs

            b. Spartina and the mussel, Geukensia demissa
 
        3. disturbance
            a. Ice scours
            b. High tides and wrack

            c. Salt build-up in mid-marsh
            d. Salt-tolerant spikegrass (Distichlis) invasion
            e. When the sediment is covered with spikegrass, evaporation decreases, salinity decreases, and other more competitively dominant plants invade

        4. grazers generally have relatively little influence –
            a. periwinkles graze, but they are controlled by crab predators
            b. geese, wild boar, feral horses and nutria
V. Productivity
    A. Productivity is high, mostly from vascular plants
        1. Vascular plants -- 50-3,000 g C/m2/yr depending on latitude and nutrients
        2. Algal production lower -- from 20-60% of vascular plant production
    B. Evidence for nitrogen limitation (addition of N changes outcome of competition)

VI. Interactions and Food Webs
    A. Few herbivores – salt marsh plants high in salt, contain lots of silica and cellulose, and are low in nutrients; some have chemical defense compounds

    B. At times grazing is important; snow geese, periwinkles
    C.~90% of the production becomes detritus
    D. Some of that carbon and energy may be exported beyond the marsh

    E. Many organisms migrate in and out of the marsh with the tides
    F. Oysters and mussels historically formed dense beds at the edges of coastal salt marshes;
            filtered incoming water, transferring lots of nutrients in fecal material to the marshes;
            over-harvesting, diseases and eutrophication have caused massive declines in these shellfish and degradation of marshes
     G. Role of predators; blue crabs, fish

Human Interactions with Estuaries and Salt Marshes
I. ‘Ecosystem services’
    A. Shelter coasts from erosion
    B. Salt marshes filter sediments and nutrients from the water column, reducing turbidity and eutrophication in the estuaries
    C. Habitat for waterfowl and migrating birds
    D. Support fisheries – shrimp, shellfish
    E. Nurseries for many juvenile fish
II. Human Impacts
    A. Traditionally thought of as wastelands that should be reclaimed for human use -- housing developments,
            marinas, seaports, industrial parks, cities, garbage dumps…
        1. Dikes and drainages; fill
        2. 1/3 of all estuaries in the US are completely gone
        3. dredging of navigation channels increases exposure of estuaries and marshes to wave action
    B. Rivers input modifications
        1. carry pollutants
        2. carry extra nutrients leading to eutrophication
            a. phytoplankton blooms (some toxic)
            b. anoxia – mouth of Mississippi and the Gulf of Mexico (‘dead zone’); Chesapeake
        3. damming and diversion often reduces freshwater flow from rivers
    C. Exotic species – ports and ballast water
        1. Asian clam, 10,000 clams/m2 in SF Bay
        2. green crab in NE U.S. – voracious predator, including on economically important shellfish
        3. nutria
        4. >200 exotics in San Francisco Bay
        5. cordgrass (Spartina) has also been transplanted to other parts of the world (Europe, China), covering mud flats and oysterbeds \
        6. phragmites

    D. Salt marsh restoration
        1. restore tidal flow by unblocking connections to the sea
        2. dredge some accumulated settlements
        3. seed/transplant Spartina
        4. attract birds with decoys and solar-powered tape recorders with bird calls


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