Chapter 15 - Ecosystem Structure of Tidal Saline Marshes

Abstract

Salt marshes are among the most valuable and productive ecosystems in the world, occurring as coastal features that often fringe shorelines and which often dominate vegetated areas of estuarine environments. Salt marshes vary from small and discrete to broad and expansive marshes and are typically located in sheltered, low-energy shoreline areas forming the interface between marine and terrestrial environments. The largest concentrations of tidal marshes are found along the South Atlantic and Gulf coasts of North America followed by China. The distribution of plant species is determined by the physical, chemical, and biological environment, with flooding and salinity as the primary variables influencing distribution. Salt marshes are generally replaced by mangrove swamps in coastal regions of the tropics and subtropics. Benthic algae occur on the sediments below and adjacent to the emergent vegetation of tidal saline marshes, as well as on the culms of the emergent vegetation (epiphytic algae). Tidal saline marshes are important habitat for organism use, including spawning, feeding, migration, and nursery (growth and refuge), among other important uses. The importance for a wide range of nekton species is well-documented. Very few species of snakes, turtles, and crocodilians can be considered common residents of tidal saline marshes; however, large number of amphibian and reptile species are occasional visitors but prefer brackish and fresh marshes. Typically, saline marsh avifauna is dominated, at least numerically, by large numbers of Anseriformes (waterfowl), Ciconiiformes (long-legged wading birds), and Charadriiformes (shorebirds, gulls, and terns). In addition, Passeriformes (songbirds) feed and breed in saline marshes. The total number of mammalian species, whose habitat primarily consists of tidal marshes, has been estimated to range from 13 to 26, with rodents predominant. Of these, only the salt marsh harvest mouse (Reithrodontomys raviventris) is restricted to coastal marshes. A full understanding of salt marsh ecosystems and their ecological structure is critical, given the global distribution of these productive ecosystems, their unique dynamics, and susceptibility to anthropogenic stresses.