The Biogeomorphology of Mangroves and Their Role in Natural Hazards Mitigation



Along low-relief coasts in tropical regions, mangroves occupy the biogeographical landscape usually occupied by salt-marsh or cypress ecosystems in more temperate regions. Over 50 species of mangroves are found worldwide. In tropical regions, mangroves are the prevalent coastal wetland ecosystem, overshadowed in the public mind by tropical rainforests and coral reefs. Mangroves exist on the tropical rims of all continents except Antarctica. Numerous species of mangroves exist; collectively they create large ecosystems such as the Sundarbans in Bangladesh and India that provide habitats for endangered species, including the Bengal Tiger. As biogeomorphological agents, mangroves interact with tidal flows to entrap and stabilize sediment, create humus, and alter tropical coastal environments. Mangrove sediments and pollen entrapped therein record substantial sea-level rises and falls during the Holocene, including a mid-Holocene highstand, and a regression associated with the Little Ice Age. Mangroves provide habitats for a variety of coastal creatures, including crabs, juvenile fish, and sponges. Worldwide, the mangrove ecosystem is threatened by anthropogenic activities such as aquaculture, urban development, and forestry. Removal of mangroves not only endangers sensitive ecosystems, but also reduces the protection from natural hazards that mangroves offer. Tsunami and storm surges from tropical cyclones are dissipated by the intertwined root systems of the mangroves, limiting the destructive potential of the surging water, although the extent of protection offered by mangroves is controversial. The natural protection of the mangroves has proven superior to man-made objects to deflect tsunami and storm surge. Mangrove revegetation efforts are underway in numerous countries, most notably Bangladesh, Vietnam, Thailand, and Tanzania. A variety of remote-sensing platforms provide the ability to monitor mangrove recovery or decline around the world. The ultimate results of anthropogenic influences on mangroves remain to be seen.