Salt Marshes

Salt marshes are coastal wetlands rich in marine life. They are sometimes called tidal marshes, because they occur in the zone between low and high tides. Salt marsh plants cannot grow where waves are strong, but they thrive along low-energy coasts.

Where are Marshes Located? What are Their Features? Salt marshes are transitional areas between land and water, occurring along the intertidal shore of estuaries and sounds where salinity (salt content) ranges from near ocean strength to near fresh in upriver marshes. Because many salt marshes are influenced by the twice daily rise and fall of tides, they are subject to rapid changes in salinity, temperature and water depth.

Salinity, frequency and extent of flooding of the marsh determine the types of plants and animals found there. The low marsh zone floods twice daily in most UK environments, while the high marsh floods only during storms and unusually high tides. Animals and plants live in these zones of the marsh, depending on how well they can withstand the drier conditions of the upper marsh or the wet conditions that regularly occur in the lower marsh.

The Vegetation Salt marsh plants are adapted to a harsh, semi-aquatic environment and saline soils. Species diversity is low. Stout stems, small leaves, and physiological adaptations for salt excretion and gas exchange characterize the inhabitants of the salt marsh, which are mostly grasses and low perennial herbs.

The tangle of marsh plant roots and stems helps to stabilize the muddy bottom, as well as to trap debris and dissolved nutrients with each tidal cycle. Bacteria convert this oasis of detritus into food resources for microscopic algae, invertebrate larvae, and larger animals. Salt marshes are about twice as photo-synthetically productive as corn fields and provide critical nursery grounds for numerous organisms.

Algae and sea lettuce

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Species composition and zonation Species composition and zonation in the salt marsh are governed by salinity gradients in combination with the amount of intertidal exposure.

Eelgrass, Zostera marina, for example, occupies the lowest or most marine zone. It cannot tolerate a freshwater environment or intertidal conditions that would expose its roots to air.

Cordgrass, Spartina foliosa, occurs in the marine-to-terrestrial transition zone, characterized by lower salinity and periodic exposure to the air. Shoreward, where conditions are even drier, species belonging to the genus Salicornia are common.

Cord Grass

On higher ground, where tidal intrusions are rare, the wiry, prickly-leaved succulent jaumea, Jaumea carnosa, is common, as are the bushy shoregrass, Monanthochloe littoralis; tall and slender sea arrowgrass, Triglochin maritima; and endangered salt marsh bird's beak, Cordylanthus maritimus.

Jaumea carnosa Monanthochloe littoralis

Triglochin maritima Cordylanthus maritimus

The green, wiry-leaved saltgrass, Distichlis spicata, is widespread, occurring from the middle to high marsh, as well as in dunes and on salt flats. An unusual salt marsh plant is the orange, parasitic dodder, Cuscuta salina. Its tiny, scale-like leaves and thread-like stems frequently invade and cover large areas of vegetation.

Salt Grass