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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 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


Acrostichum aureum Golden leather fern
Avicennia germinans Black mangrove
Baccharis halmifolia Eastern baccharis
Batis maritima Saltwort
Borrichia frutescens Bushy sea oxeye
Casuarina equistifolia Australian pine *Non-native*
Cladium mariscus ssp. jamaicense Jamaica swamp grass
Conocarpus erecta Buttonwood
Cyperus spp. Flatsedges
Distichlis spicata Desert saltgrass
Fimbristylis castanea Marsh fimbry
Hymenocallis palmeri Alligator lily
Iva frutescens Bigleaf sumpweed
Juncus roemerianus Needlegrass rush
Laguncularia racemosa White mangrove
Limonium carolinianum Carolina sea lavender
Lycium carolinianum Carolina desert thorn
Monanthochloe littoralis Shoregrass
Paspalum vaginatum Seashore paspalum
Rhizophora mangle Red mangrove
Salicornia bigelovii Dwarf glasswort
Salicornia virginica Virginia glasswort
Salsola kali Russian thistle
Sarcocornia perennis Chickenclaws
Schinus terebinthifolius Brazilian pepper *Non-native*
Schoenoplectus robustus Sturdy bulrush
Sesuvium portulacastrum Shoreline seapurslane
Solidago sempervirens Seaside goldenrod
Spartina alterniflora Smooth cordgrass
Spartina bakeri Sand corgrass
Spartina patens Saltmeadow cordgrass
Sporobolus virginicus Seashore dropseed
Suaeda linearis Altantic sea blite
Typha domingensis Southern cattail


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


Aedes sollicitans Salt marsh mosquito
Aedes taeniorhynchus Mosquito
Orchelimum fidicinium Grasshopper


Acartia tonsa Copepod
Callinectes sapidus Blue crab
Cerithidea spp. Hornsnails
Crassostrea virginica Eastern oyster
Cyathura polita Isopod
Geukensia demissa Ribbed mussel
Littorina irrorata Marsh periwinkle
Melampus bidentatus Eastern melampus
Melampus coffeus Coffee bean snail
Neanthes succinea Polychaete worm
Palaemonetes spp. Grass shrimps
Panaeus spp. Shrimps
Polymesoda caroliniana Carolina marsh clam
Scoloplos fragilis Polychaete worm
Sesarma spp. Marsh crabs
Uca spp. Fiddler crabs


Alligator mississippiensis American alligator
Malaclemys terrapin Diamondback terrapin
Nerodia clarkii taeniata Atlantic saltmarsh snake
Rana sphenocephala Southern leopard frog


Achirus lineatus Lined sole
Anchoa mitchilli Bay anchovy
Archosargus probatocephalus Sheepshead
Brevoortia spp. Menhadens
Centropomus undecimalis Common snook
Cynoscion spp. Seatrouts
Cyprinodon variegatus Sheepshead minnow
Diapterus auratus Irish pompano
Dormitator maculatus Fat sleeper
Elops saurus Ladyfish
Eucinostomus gula Silver jenny
Eucinostomus harengulus Tidewater mojarra
Eucinostomus spp. Mojarras
Fundulus confluentus Marsh killifish
Fundulus grandis Gulf killifish
Gambusia affinis Mosquitofish
Gerres cinereus Yellowfin mojarra
Gobionellus oceanicus Highfin goby
Gobiosoma bosc Naked goby
Lagodon rhomboides Pinfish
Leiostomus xanthurus Spot
Lucania parva Rainwater killifish
Lujanus griseus Gray snapper
Megalops atlanticus Tarpon
Menidia beryllina Tidewater silverside
Menticirrhus spp. Kingfishes
Microgobius gulosus Clown goby
Mugil cephalus Striped mullet
Mugil curema White mullet
Oligoplites saurus Leatherjacket
Poecilia latipinna Sailfin molly
Pogonias cromis Black drum
Sarotherodon malanotheron Blackchin tilapia *Non-native*
Sciaenops ocellatus Red drum
Strongylura notata Redfin needlefish


Ajaia ajaja Roseate spoonbill
Ardea herodias Great blue heron
Bubulcus ibis Cattle egret *Non-native*
Butorides striatus Green-backed heron
Casmerodius albus Great egret
Catoptrophorus semipalmatus Willet
Cistothorus palustris Marsh wren
Corbus ossifragus Fish crow
Egretta thula Snowy egret
Egretta tricolor Tricolor heron
Haematopus palliatus American oystercatcher
Haliaeetus leucocephalus Bald eagle
Mycteria americana Wood stork
Pandion haliaetus Osprey
Rallus longirostris Clapper rail
Rynchops niger Black skimmer
Sterna antillarum Least tern
Sterna dougalli Roseate tern


Microtus pennsylvanicus Meadow vole
Mustela vison American mink
Myocastor coypus Nutria *Non-native*
Neofiber alleni Round-tailed muskrat
Oryzomys palustris natator Silver rice rat
Peromyscus gossypinus Cotton mouse
Procyon lotor Common raccoon
Sigmodon hispidus Hispid cotton rat
Sylbilagus palustris Marsh rabbit
Tursiops truncatus Bottlenose dolphin


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