Ecosystems dominated by mangroves -- that loose confederacy of trees specially adapted to estuarine and intertidal zones -- are among the most productive and complex in the world. Massive quantities of decaying leaves, twigs and roots combine with an influx of organic matter from out-flowing rivers and incoming tides to anchor a rich food web. Terrestrial and aquatic animals, as well as species straddling those realms, all mingle here.
From Florida to Indonesia, mangrove swamps tend to proliferate at the margins of land and ocean: along the banks of coastal rivers, in intertidal basins and on sandbars and islets in estuaries and nearshore waters. The tropical trees called mangroves aren’t necessarily closely related to one another, but exhibit analogous adaptations -- such as stilt roots and salt-excreting leaves -- to contend with their brackish habitat. With the relentless mixing of waters and the density of the vegetation, massive quantities of detritus provide ecosystem fuel: Red mangroves in riverine forests, for example, may annually produce about four tons of organic matter per acre.
Nurseries and Rookeries
The protective shelter of mangrove roots and the magnitude of the food supply make mangrove ecosystems ideal nurseries for many marine organisms, from crustaceans to large ocean-going fish. This is one reason mangroves play such an important role in commercial fisheries across much of the globe. Wading birds and seabirds often rear their young in huge mangrove rookeries, taking advantage of the resources and the relative inaccessibility of the forest canopy to terrestrial predators.
Invertebrates play critical roles in mangrove ecosystems. Crabs of many kinds flourish in these estuarine forests, feeding on leaf litter and insects while falling prey themselves to birds, juvenile fish and other predators. Tidal fluctuations help dictate the foraging schedules of mangrove animals: High tide may bring in marine fish and sea snakes pursuing invertebrates and smaller fish in the water column, while hermit crabs, mudskippers, raccoons and other mudflat hunters emerge at low tide. Where seagrass pastures intermingle with mangrove islets in lagoons and estuaries in the Americas, West Africa and Australia, the huge herbivorous marine mammals called manatees and dugongs may also utilize the habitat.
In many parts of the world, mangrove swamps notably harbor large predators crowning their rich food webs. Where they aren’t persecuted by human beings, crocodiles tend to excel in these intertidal environments: Estuarine crocs are well-distributed in the mangrove wilds of South and Southeast Asia and Australasia, and from South Florida to Ecuador have a counterpart in the American crocodile. Sharks are also important mangrove predators worldwide. A famous and unique population of Bengal tigers resides in the vast Sundarbans mangrove swamps along the Bay of Bengal, one of the finest remaining refuges for these magnificent big cats.