Habitats within the salt marsh vary with elevation, micro-topography, and proximity to land or deeper water. In southern California, the high marsh, marsh plain, and cordgrass (Spartina foliosa) habitat tend to follow elevation contours, although cordgrass is often restricted to low elevations adjacent to bay and channel margins. Other habitats are related to minor variations in topography, which impound fresh or tidal water. For example, back-levee depressions, tidal pools, and salt pans occur where drainage is somewhat impaired. Salt marshes along the Atlantic Coast of USA are very extensive, with S. alterniflora creating a monotype except for a narrow transition at the inland boundary where succulent halo-phytes or salt pans are found.
Tidal creeks provide diverse habitats for plants and animals. Banks are often full of crab burrows, and creek bottoms harbor burrowing invertebrates and fishes. They also serve as conduits for fish, fish larve, phyto- and zooplankton, plant propagules, sediments, and dissolved materials, which move between the salt marsh and sub-tidal channels.
Adjacent habitats can include small, unvegetated salt pans that dry and develop a salt crust, especially during neap tides. Salt pans occur where salt concentrations exceed tolerance of halophytes. During heavy rains or high tides, water fills the pan, creating temporary habitat for aquatic algae and animals and permanent habitat for the species that survive the dry spells in situ as resting stages. More extensive salt pans are sometimes called salt flats. Other nearby habitats usually include mudflats (where inundation levels exceed tolerance of halo-phytes), brackish marsh (where salinities are low enough for brackish plants to outcompete halophytes), sandy or cobble beaches (where wave force excludes herbaceous vegetation), sand dunes (where soils are too coarse and dry for salt marsh plants), and river channels (where freshwater enters the estuary and is not sufficiently saline).
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