Introduction

Salt marshes are tidal wetland environments that occur between upland and aquatic habitats. They are found along the intertidal shore of estuaries and protected coastlines in temperate regions of the Atlantic and Pacific coasts of North America.  In tropical climates mangrove swamps often take the place of salt marshes.

Salt marshes are strongly influenced by the daily rise and fall of tides.  They are subject to fluctuations in salinity, temperature and water depth. There is a range of tidal flooding that is greatest in the low marsh zone and less in the high marsh zone. The salinity (salt content) of the water and soils ranges from near ocean strength (35 parts per thousand; ppt) in the low marsh to near freshwater levels (<0.05 ppt) in the upper reaches of the high marsh and uplands. Salinity, frequency and extent of tidal flooding, and other environmental factors of the marsh determine the types of plants and animals found there. The low marsh zone floods twice daily, while the high marsh floods only during storms and unusually high tides (spring tides). Different animals and plants live in these zones of the marsh, depending on how well they can withstand the fluctuating environmental conditions and interactions with other organisms.