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Habitat Focus: Coastal Wetlands

Thursday, July 7th, 2016

A coastal wetland is an area of land that is periodically flooded and drained. In the U.S., coastal wetlands are found along the Atlantic, Gulf, Pacific and Alaskan coasts.

The U.S. is estimated to have more than 40 million acres of wetlands in coastal watersheds. The southeastern states contain the majority, more than 80%, of these wetlands.

coastal salt marsh
A salt marsh habitat, dominated by Spartina, typically found along the Northern Gulf of Mexico. Photo credit: W. Scheffel

Coastal wetlands are both non-tidal and tidal (influenced by the periodic flooding and ebbing of tidal water). The tidal coastal wetland ecosystem supports both aquatic and terrestrial species and is often associated with estuaries, which are partially enclosed bodies of water where the sea and freshwater meet. This environment can be a difficult living environment due to the fluctuating salinity (i.e. the amount of salt in seawater) and water levels (from the tidal cycle). The plants and animals that live in coastal wetlands have adapted to handle this changing environment.

marsh and mangrove
In the Chandeleur Islands, ACER’s primary study site, the coastal wetland community is comprised of Spartina and black mangroves. Photo credit: D. Byron

Along the Gulf coast, there are a number of different types of coastal wetlands including salt marshes, mangroves, bottomland hardwood swamps and freshwater marshes. While salt marshes are characterized by large flat areas of emergent grasses, rushes and sedges; mangrove habitats are dominated by several species of these salt tolerant trees. Mangroves are tropically associated species and do not survive cold fronts or freezes. However, warmer water and warmer winters have allowed mangroves to move northward along the northern Gulf coast from their traditional range of southern Florida.

Coastal wetlands are very important habitats for many types of animals including birds, reptiles, mammals, insects and many other invertebrates. They provide food, shelter and nursery habitat for fish, shellfish and crustaceans many of which are commercially and recreationally important such as the blue crab, brown shrimp and red drum. Some of these species may use the wetland year round, while others may only use the wetland for migration or spawning.

In addition to providing habitat, coastal wetlands also provide other ecosystem services including shoreline protection from flooding and storm surge, erosion control, nutrient removal, water filtration, and carbon storage (i.e. the process where carbon dioxide is removed from the atmosphere and stored). Economically, coastal wetlands play an important role too; the economic activity generated in coastal counties of the U.S. was over $6.6 trillion in 2011, which accounted for 45% of the nation’s gross domestic product[2].

eroding salt marsh
Eroding salt marsh edge found in coastal Alabama. Photo credit: J. Moody

However, natural and human-induced impacts are causing wetland decline. In a study by the National Oceanic and Atmospheric Association (NOAA), seventy-one percent of the estimated U.S coastal wetland loss from 2001-2009 occurred in the Gulf with a loss of 257,150 acres[1]. In coastal Louisiana this loss amounts to roughly the size of a football field every 30 minutes[3]. Across the U.S., many federal programs now protect coastal wetlands and help manage and regulate activities that may affect them such as dredging, waste disposal and human recreational use. Restoration and long-term monitoring programs have also been developed to return impacted areas to their former conditions as a functional habitat.

Given the important ecosystem services coastal wetlands provide to coastal communities, ACER scientists are investigating the impact of the oil spill on this habitat by comparing oiled to non-oiled areas in the Chandeleur Islands and measuring a variety of ecosystem services from nitrogen cycling to habitat quality for associated animals.


[1] T.E. Dahl and S.M. Stedman. 2013. Status and trends of wetlands in the coastal watersheds of the Conterminous United States 2004 to 2009. U.S. Department of the Interior, Fish and Wildlife Service and National Oceanic and Atmospheric Administration, National Marine Fisheries Service. (46 p.) Available online here

[2] National Oceanic and Atmospheric Administration. 2012. Spatial trends in coastal socioeconomics. Online resource:

[3] National Wildlife Federation. Mississippi River Delta. Online resource: