Peat, a collection of decomposed plant material and roots, acts like a filter. It helps to purify fresh water runoff from the upland region. In addition this dense material captures nutrients that are brought in with the ocean tides. The marsh also serves as a protective habitat for migratory birds. The components of the marsh, the peat, grasses and shrubs, protect and stabilize shorelines from erosion and help prevent flooding.
Salt marshes are the second most biologically productive area in the world after rain forests.
They make efficient use of sunlight and have been known to produce four times as much food as an acre of rich cornland.