Mangroves are restricted to tropics and subtropics. They are absent from much of central and Western Pacific where reefs thrive, and very sparsely distributed in arid regions of the northern Red Sea and Arabian Gulf; also absent from most oceanic atolls. They currently cover about 24,000,000 hectares. There are 12 genera in 8 different families.
Mangroves trap sediment and silt, reducing siltation to offshore areas and enabling reefs to flourish.Mangrove sediments are characterized by high organic matter, providing important organic substrates for microbial communities and nutrient regeneration. Mangroves protect coastlines from storm damage during tropical storms and hurricanes and they stabilize coastlines and build islands
Mangroves have unique adaptations to withstand extreme environmental conditions:
Mangroves support genetically diverse communities of terrestrial and aquatic animals, many that are of high environmental, economic and social value. Mangrove channels and prop root communities are important nursery areas for groupers, snappers, lobsters, crabs, mussels and oysters and other valuable species.
Their growth controlled by rainfall and freshwater input, the tidal range, salinity, wave energy, and sediment composition. They tolerate a wide variety of temperatures and salinities, but not where freezes occur more than twice per year.
They are found in terrestrial and marine habitats: wetland forests and marshes, peatlands, sedge marshes, riparian swamp and riparian forests, coastal dunes, seagrass beds, coral reefs and rocky coasts (Conocarpus, right).
Mangroves vary in ecological development, from scrub vegetation found to well developed stands 40-50 meters tall .
Black mangroves produce pneumatophores which extend from the roots upward out of the sediment to help transport oxygen to the roots
Mangrove prop roots support an abundant epibiont community that recycle water column nutrients and attract high-level consumers that can make additional nutrients available via excretion.
The Red Mangrove produces seeds that germinate and grow 6-12 inches while attached to the tree (viviparous seeds; center and rigth). These seedlings (propagules, or sea pencil) are basically a long tap root topped by a small bud. If they fall off at low tide the tap root will spear itself in the much and grow there; if it falls off at high tide it floats, the root tip absorbs water, causing it to turn upright. Large seeds of black mangrove (left).
Red mangrove's prop roots anchor them to shifting sediments
Some species have salt glands at the base of their leaves excrete salts as they take up seawater.
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