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Salt Marsh Habitats


Salt Marshes Defined

Salt marshes form in sheltered coastal areas where sediments accumulate and allow growth of angiosperm plants (Pennings & Bertness 2001) that comprise the foundation of the ecosystem. Salt marshes develop between terrestrial and marine environments, resulting in biologically diverse communities adapted for harsh environmental conditions including desiccation, flooding, and extreme temperature and salinity fluctuations. Marshes act as nurseries to a wide variety of organisms, some of which are notably threatened or marketed as important fisheries species.

Rapid growth of marsh vegetation and utilization of incoming nutrients make salt marshes highly productive systems, often yielding 2 kg of aboveground production per square meter, annually (Marinucci 1982, Dame 1989). In addition to providing habitat and food sources for many organisms, salt marshes benefit humans and surrounding ecosystems by sheltering coasts from erosion and filtering nutrients and sediments from the water column.

Plant Adaptations

Flooding & Anoxia

As intertidal habitats, much of the vegetation in salt marshes experiences periodic tidal flooding. Low and mid marsh areas can be submerged for hours, and high marshes can experience storm surge that can affect more upland vegetation. The frequency and duration of flooding events, as well as the tolerance of individual species to saltwater submersion, is a major determinant of salt marsh zonation. Zonation occurs when various salt marsh plant species thrive in specific elevation ranges.

Lower limits of plant zonation are usually set by environmental tolerances, while upper limits are mainly the result of interspecific competition (Pennings & Bertness 2001). Some plants, such as Spartina alterniflora, can withstand and are even limited to areas that receive substantial flooding (Montague & Wiegert 1990). Other vegetation, like Juncus roemerianus, prefers less frequent flooding (Eleuterius & Eleuterius 1979). Submersion in water can create a host of problems for vegetation including increased intake or loss of salts through tissues and greater exposure to aqueous toxins (Adam 1990). Waterlogged soil and high levels of decaying material can deplete oxygen, creating anoxic sediments and producing toxic sulfides (Ponnamperuma 1972, Drake 1989, Adam 1990, Pezeshki 1997).

Most plants that grow in anoxic soil produce adventitious roots near the sediment surface to facilitate oxygen uptake. For example, frequently flooded plants like S. alterniflora grow roots in the top 3 cm of the sediment that help oxygenate deeper roots (Anderson 1974). Some plants also have a well-developed system of air passages called aerenchyma tissue, which transfer oxygen from the atmosphere to submerged roots (Ponnamperuma 1972, Armstrong 1979).

Salinity

Salinity in salt marshes is highly variable because of the influx of both fresh and saltwater into the environment. Freshwater enters upland marsh areas from terrestrial streams and rivers, increasing during periods of high precipitation. Saltwater inundates marshes during high tides, with dry seasons and high evaporation further increasing salinity. Salinity gradients caused by these processes contribute to zonation in marsh plants based on salt tolerance among species.

Most angiosperms have a limited ability to thrive in saline waters, and diversity of vegetation decreases with increasing salinity (Odum 1988, Odum & Hoover 1988). Seeds and seedlings are especially vulnerable to salt stress, further contributing to zonation in plants. However, many salt marsh plants have developed mechanisms to tolerate high salinities. Some plants increase succulence by retaining water or exclude salt at the roots, while others excrete salt through specialized glands or sequester it into leaves that are shed periodically (Poljakoff-Mayber 1975, Rozema et al. 1981, Hacker & Bertness 1995, Mitsch & Gosselink 1993, Dawes 1998).
Perhaps one of the greatest stresses for salt marsh plants to overcome is the difficulty of roots to take up water due to the lowered water potential of salty soil, which averages 10 to 20 ppt, but may exceed 100 ppt in some areas such as salt pans (see below) (Wiegert & Freeman 1990). Many marsh plants adjust to this physiological strain by accumulating sugars and other organic solutes in their tissues, thereby increasing the vascular pressure needed to absorb water from the soil (Flowers et al. 1977, 1986; Rozema et al. 1985).

Distribution & Regional Occurrence

Salt marsh habitats are found at nearly all latitudes, transitioning into mangrove forests in the tropics/subtropics (Chapman 1960, Costa & Davy 1992). In the United States, the majority of the four million acres of salt marshes (Field et al. 1991) are along the east coast from Maine to Florida and along the Gulf of Mexico coastline. Few marshes exist on the Pacific coast of the U.S. due to high wave energy and mountainous terrain, but extensive marshes can be found in Alaska. Florida is home to an estimated 420,000 acres of salt marsh, with 70% in the northern part of the state, 20% in the south, and 10% in the Indian River Lagoon (IRL) (Montague & Wiegert 1990). The majority of marshes in the IRL are concentrated in the northern half of the system.

Types of Communities

Salt Marsh - Mangrove Transition

Marshes in South Florida, including the Everglades and Ten Thousand Islands, are predominantly transition areas where salt marsh plants grow in peat substrata formed around mangroves and buttonwoods (Schomer & Drew 1982). The black mangrove, Avicennia germinans, is particularly common in this community, growing alongside Baccharis, Salicornia, Batis, Distichlis, Borrichia and Iva species. Fresh and saltwater influences in these areas create harsh environments with wide salinity fluctuations that help to balance growth between vegetation.

High Marsh

High marsh occurs in areas above the mean high water mark and is not commonly flooded by tides (Montague & Wiegert 1990). Stands of Spartina, Juncus, Salicornia and Distichlis are mixed with various mangrove species. On the east coast of South Florida around Biscayne Bay, high marshes are often dominated by Spartina, transitioning to large Juncus populations toward the Homestead region (Montague & Wiegert 1990). High marsh is also the most common salt marsh community in the IRL.

Oligohaline Marsh

Oligohaline marsh forms where large influxes of freshwater enter the salt marsh ecosystem. Here, vegetation is a mixture of both marine and estuarine plants that tolerate low salinities, such as: needlegrass rush, Juncus roemerianus; golden leather fern, Acrostichum aureum; cattail, Typha domiguensis; and Jamaica swamp grass, Cladium mariscus ssp. jamaicense (FWS 1999). The creation of mosquito impoundments has shifted many of the marshes in the IRL toward this type of community.

Salt Pans

Salt pans form in low-latitude marshes where high soil salinities of 100 ppt or greater create bare patches devoid of vegetation. These barrens are often bordered by highly salt-tolerant plants (Stout 1984, Callaway et al. 1990, Wiegert & Freeman 1990, Clewell 1997, Nomann & Pennings 1998, Pennings & Richards 1998) including saltworts, glassworts and Juncus spp. (FWS 1999). Salt pans are prevalent throughout Florida marshes, but are most common along the southwest coast. As typically well-drained areas, salt pans should not be confused with salt ponds, which hold standing water in high-latitude marshes (Pennings & Bertness 2001).

Salt Marsh Algae

Salt marshes are home to several hundred species of microalgae and numerous attached or drift macroalgae (Montague & Wiegert 1990, Wiegert & Freeman 1990). While the total biomass of vascular plants in salt marshes most likely outweighs that of many algal species, algae may be more productive as a whole. Algae growth and decay is more rapid, and organisms can assimilate energy from algal communities more quickly than vascular plants, which often must be broken down by bacterial processes prior to consumption (Adam 1990). In addition to macroalgae providing a habitat and food source for fishes and invertebrates, microalgae also plays an important role in salt marsh ecosystems.

A variety of filter feeders and zooplankton feed on phytoplankton, and benthic diatoms and cyanobacteria form mats that stabilize sediment on mud flats, possibly allowing subsequent colonization of salt marsh vegetation (Coles 1979). For a list of some of the most common algal species in IRL salt marshes, please refer to the table at the bottom of this page.

Salt Marsh Inhabitants

As described above, salt marsh vegetation can vary between community types. However, the most common genera of foundation plants in Florida marshes include Spartina, Juncus, Distichlis and Batis. These vascular plants and associated algae provide habitat and food for a variety of fishes, birds, mammals, insects and other invertebrates. According to the Florida Natural Areas Inventory (FNAI) of 1997, local salt marshes support at least 10 species of fishes, 33 birds, 12 mammals and five vascular plants that are considered to be rare or endangered.

Many salt marsh organisms have a substantial impact of the health of the system. For example, herbivores and detritivores break down and consume large amounts of organic material produced by plants and algae, and fiddler crabs excavate complex burrows that aerate the soil and promote growth of Spartina spp. (Montague 1982). Countless instances of species interactions exist in salt marshes worldwide, many of which are fundamental to the health and longevity of these habitats and their corresponding food webs.

The following table is an abbreviated list of salt marsh organisms. Select available links to learn more. Additional species reports can be found in the alphabetized lists of this site.

Scientific Name Common Name

PLANTS

Acrostichum aureumGolden Leather Fern, Mangrove Fern, Swamp Fern
Avicennia germinansBlack Mangrove
Baccharis halimifoliaEastern Baccharis
Batis maritimaSaltwort, Turtleweed
Bolboschoenus robustusSturdy Bulrush
Borrichia frutescensBushy Seaoxeye
Casuarina equisetifoliaAustralian Beefwood, Australian Pine, Beach She-oak,
Ironwood
Cladium mariscus ssp. jamaicenseJamaica Swamp Sawgrass
Conocarpus erectaButtonwood
Cyperus spp.
Distichlis spicataSaltgrass
Fimbristylis castaneaMarsh Fimbry
Hymenocallis palmeriAlligator lily
Iva frutescensBigleaf Sumpweed
Juncus roemerianusBlack Needle Rush
Laguncularia racemosaWhite Mangrove
Limonium carolinianumSea Lavender
Lycium carolinianumChristmas Berry
Monanthochloe littoralisShoregrass
Paspalum vaginatumJointgrass
Rhizophora mangleAmerican Mangrove, Mangrove, Red Mangrove
Salicornia bigeloviiDwarf Saltwort
Salicornia virginicaPerrenial Glasswort
Salsola kaliRussian Thistle
Sarcocornia perennisChickenclaws
Schinus terebinthifoliusBrazilian Pepper-tree, Brazilian Peppertree, Christmas
Berry, Christmasberry, Faux Poivrier, Florida Holly, Warui
Sesuvium portulacastrumShoreline Seapurslane
Solidago sempervirensSeaside Goldenrod
Spartina alternifloraSmooth Cordgrass
Spartina bakeriSand Cordgrass
Spartina patensSalt Meadow Cordgrass
Sporobolus virginicusSeashore Dropseed
Suaeda linearisSea Blite
Typha domingensisSouthern Cattail

ALGAE & OTHER PROTISTS

Bostrychia spp.Red algae
Cylindrotheca spp.Diatoms
Enteromorpha spp.Green algae
Gyrosigma spp.Diatoms
Lyngbya spp.Cyanobacteria
Navicula spp.Diatoms
Nitzschia spp.Diatoms
Rhizoclonium spp.Green algae
Ulva spp.Green algae

INSECTS

Aedes sollicitansSalt marsh mosquito
Aedes taeniorhynchusMosquito
Orchelimum fidiciniumGrasshopper

AQUATIC INVERTEBRATES

Acartia tonsaCalanoid copepod
Callinectes sapidusBlue Crab
Cerithidea spp.Hornsnails
Crassostrea virginicaAmerican Oyster, Atlantic Oyster, Common Oyster, Eastern
Oyster, Virginia Oyster
Cyathura politaIsopod
Geukensia demissaRibbed Horsemussel, Ribbed Mussel
Littorina irrorataMarsh Periwinkle
Melampus bidentatusEastern Melampus
Melampus coffeusCoffee Bean Snail, Coffee Melampus
Neanthes succineaClam Worm, Pileworm, Ragworm
Palaemonetes spp.Grass shrimp
Penaeus spp.Shrimps
Polymesoda carolinianaCarolina marsh clam
Scoloplos fragilisPolychaete worm
Sesarma spp.Marsh crabs
Uca spp.Fiddler crabs

REPTILES & AMPHIBIANS

Alligator mississippiensisAmerican Alligator
Malaclemys terrapinDiamondback terrapin
Nerodia clarkii taeniataAtlantic Salt Marsh Snake
Rana sphenocephala

FISHES

Achirus lineatusLined Sole
Anchoa mitchilliBay Anchovy
Archosargus probatocephalusConvict Fish, Sheepshead, Sheepshead Bream, Sheepshead
Porgie
Brevoortia spp.Menhadens
Centropomus undecimalisCommon Snook, Robalo, Thin Snook
Cynoscion spp.Seatrouts
Cyprinodon variegatusSheepshead Minnow
Diapterus auratusIrish Pompano
Dormitator maculatusFat Sleeper
Elops saurusLadyfish
Eucinostomus spp.Mojarras
Eucinostomus gulaSilver Jenny
Eucinostomus harengulusTidewater mojarra
Fundulus confluentusMarsh Killifish
Fundulus grandisGulf Killifish
Gambusia affinisMosquitofish, Western Mosquitofish
Gerres cinereusYellowfin Mojarra
Gobionellus oceanicusHighfin goby
Gobiosoma boscNaked Goby
Lagodon rhomboidesPinfish
Leiostomus xanthurusChub, Flat Croaker, Golden Croaker, Goody, Jimmy, Roach,
Silver Gudgeon, Spot, Spot Croaker
Lucania parvaRainwater Killifish
Lutjanus griseusBlack Snapper, Gray Snapper, Lowyer, Mango Snapper, Mangrove
Snapper
Megalops atlanticusTarpon
Menidia beryllinaTidewater Silverside
Menticirrhus spp.Kingfishes
Microgobius gulosusClown Goby
Mugil cephalusBlack Mullet, Flathead Mullet, Gray Mullet, Sea Mullet,
Striped Mullet
Mugil curemaSilver Mullet, White Mullet
Oligoplites saurusLeatherjacket
Poecilia latipinnaSailfin Molly, Topote Velo Negro
Pogonias cromisBlack Drum, Corvina Negra, Tambor Negro
Sarotherodon melanotheronBlackchin Mouthbreeder, Blackchin Tilapia
Sciaenops ocellatusCorvineta Ocelada, Red Drum
Strongylura notata

BIRDS

Ajaia ajaiaRoseate Spoonbill
Ardea herodiasGreat Blue Heron
Bubulcus ibisBuff-backed Heron, Cattle Egret, Elephant Bird, Hippopotomus
Egret., Rhinoceros Egret
Butorides striataGreen-backed Heron
Casmerodius albus
Catoptrophorus semipalmatus
Cistothorus palustrisMarsh Wren
Corvus ossifragusFish Crow
Egretta thulaSnowy Egret
Egretta tricolorLouisiana Heron, Tricolored Heron
Haematopus palliatusAmerican Oystercatcher
Haliaeetus leucocephalusBald Eagle
Mycteria americanaWood Stork
Pandion haliaetusOsprey
Rallus longirostrisClapper Rail
Rynchops nigerBlack Skimmer
Sterna antillarum
Sterna dougalliiRoseate Tern

MAMMALS

Microtus pennsylvanicusMeadow vole
Myocastor coypusNutria
Neofiber alleniRound-tailed Muskrat
Neovison visonAmerican mink
Oryzomys palustris natatorRice Rat
Peromyscus gossypinusCotton mouse
Procyon lotorRaccoon
Sigmodon hispidusHispid cotton rat
Sylvilagus palustrisMarsh rabbit
Tursiops truncatusBottlenose Dolphin, Bottlenosed Dolphin, Common Bottlenose
Dolphin, DelfĂ­n Tonina

REFERENCES & FURTHER READING

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Armstrong, W. 1979. Aeration in higher plants. Adv. Bot. Res. 7: 225-332.

Brockmeyer JR., RE, Rey, JR, Virnstein, RW, Gilmore, RG & L Earnest. 1997. Rehabilitation of impounded estuarine wetlands by hydrologic reconnection to the Indian River Lagoon, Florida (USA). Wetlands Ecol. Manag. 4: 93-109.

Chapman, VJ. 1960. Salt marshes and salt deserts of the world. Leonard Hill Limited. London, UK.

Coles, SM. 1979. Benthic microalgal populations on intertidal sediments and their role as precursors to salt marsh development. In: Jefferies, RL & AJ Davy, eds. Ecological processes in coastal environments. 25-42. Blackwell Scientific Publications. Oxford, UK.

Costa, CSB & AJ Davy. 1992. Coastal salt marsh communities of Latin America. In: Seeliger, U, ed. Evolutionary ecology in tropical and temperate regions: coastal plant communities of Latin America. 179-199. Academic Press. San Diego, CA. USA.

Crewz, DW & RR Lewis III. 1991. An evaluation of historical attempts to establish vegetation in marine wetlands in Florida. Florida Sea Grant technical paper TP-60. Sea Grant College, University of Florida. Gainesville, FL. USA.

Dame, RF. 1989. The importance of Spartina alterniflora to Atlantic coast estuaries. Rev. Aquat. Sci. 1: 639-660.

David, JR. 1992. The Saint Lucie County Mosquito Control District summary workplan for mosquito impoundment restoration for the salt marshes of Saint Lucie County. Saint Lucie County Mosquito Control District. Saint Lucie, FL. USA.

Dawes, CJ. 1998. Marine botany, 2nd ed. John Wiley & Sons. New York. USA. 480 pp.

Drake, BG. 1989. Photosynthesis of salt marsh species. Aquat. Bot. 34: 167-180.

Dybas, CL. 2002. Florida's Indian River Lagoon: an estuary in transition. BioScience. 52: 554-559.

Eleuterius, LN & CK Eleuterius. 1979. Tide levels and salt marsh zonation. Bull. Mar. Sci. 29: 394-400.

Field, DW, Reyer, AJ, Genovese, PV & BD Shearer. 1991. Coastal wetlands of the United States. National Oceanic and Atmospheric Administration and US Fish and Wildlife Service. Washington, DC.

FNAI. 1997. County distribution and habitats of rare and endangered species in Florida. Florida Natural Areas Inventory. Tallahassee, FL. USA.

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FWS. 1999. Coastal Salt Marsh. In: Multi-species recovery plan for South Florida. US Fish & Wildlife Service. 553-595.

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Kale II, HW. 1996. Recently extinct: dusky seaside sparrow, Ammodramas maritimus nigrescens. In: Rodgers, JA, Kale II, HW & HT Smith, eds. Rare and endangered biota of Florida. Volume V. Birds. 7-12. University Presses of Florida. Gainesville, FL. USA.

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