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 OCCURENCE
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 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

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 sollicitans

Salt marsh mosquito

Aedes taeniorhynchus

Mosquito

Orchelimum fidicinium

Grasshopper

AQUATIC INVERTEBRATES

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

REPTILES & AMPHIBIANS

Alligator mississippiensis

American alligator

Malaclemys terrapin

Diamondback terrapin

Nerodia clarkii taeniata

Atlantic saltmarsh snake

Rana sphenocephala

Southern leopard frog

FISHES

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

BIRDS

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

MAMMALS

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


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.

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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.

Flowers, TJ, Troke, PF & AR Yeo. 1977. The mechanism of salt tolerance in halophytes. Ann. Rev. Plant Physiol. 28: 89-121.

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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.

Klassen, CA. 1998. The utilization of a Florida salt marsh mosquito impoundment by transient fish species. Master’s Thesis. Florida Inst. of Technology. 87 pp.

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