Coastal Salt Marsh

Salt marshes are found in flat, protected waters usually within the protection of a barrier island, estuary, or along low-energy coastlines. Situated between the land and the sea, salt marshes experience the effects of both salt and fresh water. Tidal effects are greatest on marsh areas below mean low water, while upland freshwater sources influence areas above mean high water. Tides flush saline waters over the intertidal zone and rivers carry freshwater in from upland sources, transporting with them sediments and nutrients necessary for the growth and formation of a marsh system. Within the low-lying protected areas, halophytic plants quickly grow and establish root systems. As tide waters flood over a marsh, suspended sediment settles out and accumulates around the stems of plants. Rivers and other upland sources also contribute sediments to the marsh by continually transporting and redepositing sediment. In the early development of a marsh, sedimentation increases and promotes the establishment and growth of additional plants. As the marsh matures, accretion slows and stabilizes with the surrounding sediment source, tidal regime, and topography. The underlying theories of formation and zonation of salt marshes have been extensively reviewed ( e.g ., Pomeroy and Wiegert 1981, Adam 1980, Montague and Wiegert 1990). One theory suggests salt marsh vegetation has the ability to trap and accumulate sediment and is responsible for its own development and zonation. The alternate theory suggests local physical and geological processes that influence topography, elevation, and water movement are responsible for the formation and zonation of salt marsh vegetation. In this view, marsh plants are not significant land builders but instead are opportunistic species that colonize those areas in which they are adapted. Both theories show evidence for the importance of both environmental and biological factors in determining the formation and structure of salt marshes.

Multiple factors interact to determine the formation, structure, and ecological processes of salt marshes including (1) climate, (2) hydrology, and (3) physical factors. Climatic factors include temperature and rainfall; hydrologic factors include tidal inundation and wave energy; and physical factors include elevation and slope, sediment and soil composition, and surface water and soil salinity. The most influential hydrologic factor of a salt marsh is tidal inundation, where the frequency and duration of tidal flooding determines the extent of the intertidal zone. Other factors that affect the hydrologic regime of a marsh are wave energy, climate, rainfall, freshwater flow, and evapotranspiration. The unique topographic features of South Florida affect the degree of submergence, which in turn influences the zonation of plant species. All of these factors are important for restoring ecological processes to salt marshes.

Taken from: U.S. Fish and Wildlife Service. 1999. South Florida Multi-Species Recovery Plan.   Atlanta, Georgia. Pp. 3:556.

Listed Species Occurring in Coastal Salt Marsh Habitat

  • Lower Keys Rabbit
  • Roseate Tern
  • Rice Rat
  • Key Deer
  • Wood Stork
  • Bald Eagle