Mangroves are woody trees or shrubs that grow in mangrove habitats or mangal (Hogarth, 1999). Mangroves grow only in tropical and subtropical tidelands, which are frequently inundated with salt water, such as estuaries and marine shorelines. Mangrove trees form a specific ecological community, denominated as mangroves.
Mangroves can thrive in salt water inundation thanks to their specialized root structures, as well as their highly adapted and specialised reproductive cycle. Crucially they have also evolved to be able to excrete salt from their system. Mangrove forests occupy about 17 million hectares of tropical coast worldwide: across Africa, Australia, Asia and the Americas.
The mangrove ecosystems provide protection against extreme weather events, such as storm winds and floods, as well as tsunamis. This is due to their capacity to absorband dissipate the tidal surges that are associated with these events. They also contribute to the functioning of adjacent ecosystems, including terrestrial wetlands, peat swamps, salt marshes, sea grass beds and coral reefs.
Biodiversity
Rich in biodiversity, mangrove ecosystems provide a habitat for wide varieties of animal and plant species. According to Hogarth, mangrove areas contain some 54 species of trees in 20 genera, belonging to 16 families that constitute the "true mangroves" — species that occur exclusively in mangrove habitats and rarely elsewhere (Hogarth, 1999).
Moreover, mangroves are home to many kinds of animal species due to the richness in food and form dynamic ecosystems. Live and decaying mangrove leaves and roots provide nutrients that nourish plankton, algae, shellfish, fish, crabs and shrimp. Many of the fish caught commercially in tropical regions reporduce, spend some time in the mangroves as juveniles or adults or depend on food chains linked to these coastal ecosystems. Mangroves are also home to many birds and mammals – such as mangrove monkeys in South Asia.
Livelihoods
Furthermore, mangrove ecosystems provide many local peoples with the basis of their livelihoods. Traditional economic activities vary from fishing and gathering of crustaceans to usages of the trees for timber or tannin production.
In economic planning, mangrove ecosystems have consistently been undervalued, usually because only their direct goods and services have been included in economic calculations (e.g. forestry resources), but this represents only a minor part of the total value of mangroves.
Next to economic value, mangroves also bear great cultural significance for local communities, such as the Concheras or shell-fishers in South America, as their identity is strongly related to the ecosystem they live in.
Mangroves under threat
Coastal habitats across the world are coming under pressuredue to increasingly heavy population and development demands. Mangroves have been particularly vulnerable to exploitation because they contain valuable wood and fisheries resources, and occupy coastal land that is easily converted to other uses.
One of the biggest threats to mangrove conservation is intensive shrimp farming, specifically due to the use of chemicals and laboratory-bred larvae. The scale of human impact on mangroves has increased dramatically over the past three decades or so, with many countries showing losses of 60-80% or more of the mangrove forest cover that existed in the 1960s.
Sources:
Hogarth, Peter J. (1999). The Biology of Mangroves. Oxford University Press, Oxford; United Kingdom;
International Tropical Timber Organization (2003)..Mangroves: forests worth their salt. www.itto.or.jp
Macintosh, D. J. and Ashton, E. C. (2002). A Review of Mangrove Biodiversity Conservation and Management. Centre for Tropical Ecosystems Research, University of Aarhus, Denmark (pdf file)