Gulf Coast Salt Marshes

The Great egret (Casmerodius albus) winters in the tidal marshes along the Gulf Coast. Photo by  USGS photographer David Seawell.

The northeast Gulf of Mexico shoreline contains about 60 percent of the coastal and freshwater marshes in the United States, including 400,000 to 500,000 acres of salt marsh in northern Florida alone. From Apalachicola Bay south to Tampa Bay, salt marshes are the main costal community.

What are salt marshes? Salt marshes are natural saline soiled communities dominated by grasslands found on the border of saltwater bodies with tidally or non-tidally fluctuating inundation. They are at least occasionally flooded by high tide, but are not flooded during low tide. Most vegetative communities cannot grow where waves are strong, but irregularly flooded communities thrive on low-energy coasts

Where do salt marshes occur? Salt marshes occur all along the Atlantic and Gulf of Mexico coasts between 25degrees N latitude and 42degrees N, reaching their northern limit on the New Jersey coast. In Florida, salt marshes are most abundant on coastlines above the winter freeze line (where they do not have to compete with mangrove wetlands), especially along the "Big Bend" area of the Gulf coast in low-energy shorelines, sands, lagoons and bays. Salt marshes occur on the Atlantic coast as well. Ten percent of Florida's salt marshes are found in the Indian River Lagoon. More than half of Florida's salt marshes are dominated by needlerush vegetation.

Salt Marsh Wildlife: Salt marshes are home to many invertebrates that feed on decomposed plant cellulose. These organisms, found most abundantly in needlerush areas, provide an important link at the base of the food chain. Gulf coast marshes are well known for their abundant crustaceans, gastropods and suspension feeders including fiddler crabs, grass shrimps, blue crabs, mysid shrimp and marsh periwinkle. The area is also home to a diversity of fish species, including sheepshead minnow, longnose killfish, sailfin molly and pinfish. The American alligator is the only reptile with significant distribution in Gulf Coast salt marshes, but also found are the Mississippi diamondback tarrapin, Alabama red-bellied turtle and Gulf salt marsh water snake. Over 60 species of birds use habitats in needlerush marshes, including year-round residents such as the great blue heron and clapper rail; summer nesting birds such as least bittern; migrants including short-billed marsh wren, sedge wren, American widgeon; casual feeders such as great white heron; and summer visitors including white ibis. Popular mammal species in the marsh are Louisiana muskrat and marsh rabbit, while the cotton rat and rice rat live in the upland, and raccoons, mink, otter and long-tailed weasel come to the marsh to feed.

Cross section of a gulf coast salt marsh. Click to enlarge. (Figure 1.Generalized diagram of Gulf coast salt marshes on protected low energy shorelines. Click to enlarge.)

Vegetation: Very few plants have the physical and physiological adaptations to grow and reproduce in saline areas with periodic flooding, so salt marsh vegetative species diversity is relatively low. Typically, the communities are composed of 90% grasses and grasslike plants, 5% woody plants and trees and 5% forbs.

Two grasslike species play unique dominating roles:

  1. Smooth cordgrass (Spartina alterniflora) forms a border along open water in salt marshes. On a broad gentle slope, smooth cordgrass occupies a monospecific band 1 to 10 meters wide; greater slopes lead to mixing of smooth cordgrass and needlerush at upper elevations.
  2. Needlerush (Juncus roemerianus) comprises the largest vegetative zone and the bulk of the biomass in most salt marshes on the northeast Gulf Coast. Needlerush is found in a small elevation range, but can span one hundred meters to several miles wide. The entire needlerush zone is flooded very irregularly - higher elevation zones flood only in spring tides and storms.

    In coastal areas with high-energy tides, needlerush and cordgrass can be found together, but more often, there is a clear separation between these zones. Other common vegetative species include: saltmeadow cordgrass, giant cordgrass, salt grass, saltworts, three-square, leafy sedge, sea lavendar, arrow leaf, roseau cane, saw grass, bullwhip, and blue flag.

Salt Marsh Soils: Salt marsh soils are diverse saline soils, predominantly sandy or clayey and shallow over a limestone base. Tidal action causes saturation of soil with salt water and inundation to a depth of a few inches. Organic matter and clay content, and pH decrease sharply with an increase in elevation across the marsh.

Ecological functions and human values: Salt marshes act as a transitional zone from terrestrial uplands to ocean life. They absorb and trap potential pollutants before they reach estuaries and fragile waterways. Salt marshes also stabilize coastal shorelines, preventing erosion and sediments from washing offshore, especially during storm tides. Widely considered one of the most productive ecosystems in the world, salt marshes produce up to 80 metric tons per hectare of plant material annually. Tidal waters distribute plant cellulose (created when plants die and decompose), and flush salt and toxins from the system, bringing in nutrients that stimulate growth. Salt marshes are important to wildlife as well. They are a habitat for early life stages of many ocean species as they feed on invertebrates and are home to many marine fishes because shallow brackish water keeps large predatory fish out. Estuaries near Gulf Coast salt marshes provide a nursery for at least 70 percent of Florida's recreational and commercial fishes, shellfish and crustaceans - all dependant on coastal wetlands.

Human impacts and threats: Salt marshes were one of the last wetland communities to be impacted by Florida's post-1930 population surge because of the high original concentration of salt marsh mosquitoes. The development of Dichlorodiphenyltrichloroethane (DDT) and practices that raised water levels to upset the mosquito breeding cycle helped make salt marshes more "habitable." Beginning in 1940, salt marsh areas near cities were filled for urban development and the establishment of ports. During the 1950s birth of Florida's tourism and space industries, 15,000 acres of salt marsh were impounded on the Atlantic coast. Today, Florida's salt marshes have suffered a less than 10% loss overall, but some urban coastal areas have faced more severe losses. From 1948 to 1978, Tampa Bay lost 40% of its salt marsh cover; Charlotte Harbor and the Indian River Lagoon have seen 51% and 85% reductions in salt marsh area coverage, respectively. Wetland mitigation and more strict regulations on dredge and fill operations have helped offset initial losses, but the population on Florida's coastlines continues to grow, pressuring for development of these natural areas.

Further Reading:

Stout, J.P. 1984. The ecology of irregularly flooded salt marshes of the north-eastern Gulf of Mexico: a community profile. U.S. Fish and Wildlife Services. Biol. Rep. 85(7.1). 98pp

Mitsch,W. J., and Gosselink, J. G. 2000. Wetlands. John Wiley & Sons, Inc. New York.

On the Web:

Department of Environmental Protection, Florida Marine Research Institute. "Salt Marshes." Last updated: 22 February 2002. Available online at:

Mullahey, J.J., Tanner, G.W, Coates, S. "Range Sites of Florida." University of Florida Institute of Food and Agricultural Sciences. Available online at:


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