Mangrove swamp is an easily recognized habitat along tropical and subtropical coastlines and brackish estuaries and deltas, where evergreen trees and shrubs thrive in tideland mud or sand flats inundated daily with sea water. These flats are found mostly along bays and inlets protected from heavy waves. Some coral reefs on islands can support mangal in relatively high energy environments.
The plant community of a mangrove swamp is most commonly termed mangal, a forest with a dense canopy, also known as mangrove swamp forest or, simply, mangrove. Although mangal occurs along more than two-thirds of all saltwater tropical coastlines, parallel to the shoreline, this is a very narrow, fringing forest, and, hence, less than one-tenth of one percent of the earth's surface is inhabited by mangal.
The saturated mud flat of the typical mangrove swamp is a hostile environment for typical plants, because the soil has very low levels of oxygen for roots and toxic levels of sulfides. Ocean water generally has 33 to 38 parts of salt per thousand, and evaporation of water from the mangrove mud results in much higher salt concentrations experienced by the plants. All species that inhabit the outer (ocean-facing) portion of the mangrove swamp are halophytes, i.e., plants that are adapted to saline soils, and certain mangrove species can tolerate soils more than double the salinity of ocean water. Species that are less resistant to salt damage grow on the landward edge of mangal, where high tides reach only infrequently, or along river banks (estuarine mangrove), where freshwater mingles with sea water due to tidal influences.
Mangrove swamp is often adjacent to one of several other habitats, e.g., salt flats with its herbaceous to succulent forms of plants, sandy beach strand, freshwater swamp, or terrestrial forest or scrub. The transition can be very abrupt, but more than half of the species that can be present in mangal occur in mangal and also the adjacent plant community (mangal associates).
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