Ecological roles(生態上的角色) of mangrove

Plants in mangrove swamps are a diverse group which have been able to exploit a habitat (the intertidal zone) because they have developed a set of physiological adaptations to overcome the problems of anoxia, salinity and frequent tidal inundation. About 110 species have been identified as belonging to the mangal.[2]. Each species has its own capabilities and solutions to these problems; this may be the primary reason why, on some shorelines, mangrove tree species show distinct zonation due to variations in the range of environmental conditions across the intertidal zone. Therefore, the mix of species at any location within the intertidal zone is partly determined by the tolerances of individual species to physical conditions, like tidal inundation and salinity, but also may be influenced by other factors such as predation of their seedlings by crabs.


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A cluster of mangroves on the banks of Vellikeel river in Kannur District of Kerala, India
Once established, the roots of the mangrove plants provide a habitat for oysters and help to impede water flow; thereby enhancing the deposition of sediment in areas where it is already occurring. It is usually the case that the fine, anoxic sediments under mangroves act as sinks for a variety of heavy (trace) metals which are scavenged from the overlying seawater by colloidal particles in the sediments. In areas of the world where mangroves have been removed for development purposes, the disturbance of these underlying sediments often creates problems of trace metal contamination of seawater and biota.
It is often stated that mangroves provide significant value in the coastal zone as a buffer against erosion, storm surge and tsunamis. While there is some attenuation of wave heights and energy as seawater passes through mangrove stands, it must be recognised that these trees typically inhabit areas of coastline where low wave energies are the norm. Therefore their capacity to ameliorate high energy events like storm surge and tsunamis is limited. Their long term impact on rates of erosion is also likely to be limited. Many river channels that wind through mangrove areas are actively eroding stands of mangroves on the outer sides of all the river bends, just as new stands of mangroves are appearing on the inner sides of these same bends where sediment is accreting.
They also provide habitats for wildlife, including several commercially important species of fish and crustacea and in at least some cases export of carbon fixed in mangroves is important in coastal foodwebs. In Vietnam, Thailand, the Philippines, and India, mangrove plantations are grown in coastal regions for the benefits they provide to coastal fisheries and other uses. Despite replanting programs, over half the world's mangroves have been lost.