Mangrove trees

Linking the land to the sea

 
 
 

Dominating many coastlines in tropical and subtropical areas, mangroves are a bridge between terrestrial and marine environments. They are also extremely productive ecosystems.

The forests transfer organic matter and energy from the land to the sea, forming the base of many marine food webs. They are also home to a wide variety of marine and terrestrial life, and serve as nurseries for many coral reef and commercially important fish species. 

In addition, mangrove forests play a vital role in trapping sediments, thereby stabilizing coastlines and protecting coral reefs and sea grass meadows.

Mangrove forests consist of diverse, salt-tolerant tree and other plant species, ranging from small shrubs to tall trees tens of metres high.

These forests are found between 32 degrees north and 38 degrees south of the equator, in sheltered, inter-tidal areas that receive a high annual rainfall. 

The most extensive area of mangroves is found in Asia, followed by Africa and South America. According to the FAO, the total mangrove area is around 150,000 km2. Four countries (Indonesia, Brazil, Nigeria, and Australia) account for about 41% percent of all mangroves. 

Although a wide variety of plant species are found in mangrove forests, only some 54 species belonging to 16 families are recognized as "true mangroves" - species which are rarely found outside mangrove habitats.

Mangrove trees have various adaptations that allow them to live in saline, tidal areas. Their dense root systems give support in the soft, water-logged sediment. In most species, the roots protrude above the soil to absorb oxygen from the air, as the sediment is oxygen-poor. 

In addition, the trees either actively exclude salt when they take up seawater through their roots, or else excrete the salt from their leaves, roots, or branches. Most mangrove species also have special adaptations for reproduction, including viviparity where seed germination begins on the tree itself.

Mangrove forests play a central role in transferring organic matter and energy from the land to marine ecosystems. 

This matter and energy comes from detritus from fallen leaves and branches, and forms the base of important marine food chains.

Bacteria break down the detritus, releasing useful nutrients into the water that can then be used by marine animals. These same bacteria give mangroves their "rotten egg" smell - as the sediment is oxygen-poor, only bacteria that use sulphur for energy can survive.

The dense root systems form a home for fish, crabs, shrimps, and molluscs. They also serve as nurseries for juvenile fish. Many coral reef fish, for example, spawn in mangrove forests. The young fish stay in the forest, where there is plenty of food and they can shelter from predators, until they are old enough to move to the reef. 

In addition, mangrove forests are nesting and migratory sites for hundreds of bird species, as well as home to a wide variety of reptile, amphibian, and mammal species. For example, the Sunderban mangroves of India and Bangladesh - the largest mangrove forest on Earth - are home to Bengal tigers, spotted deer, saltwater crocodiles, fishing cats, and various dolphin species.

Like coral reefs, mangrove forests are extremely productive ecosystems that provide numerous good and services both to the marine environment and people.

Mangrove forests are home to a large variety of fish, crab, shrimp, and mollusk species. These fisheries form an essential source of food for thousands of coastal communities around the world. The forests also serve as nurseries for many fish species, including coral reef fish. A study on the Mesoamerican reef, for example, showed that there are as many as 25 times more fish of some species on reefs close to mangrove areas than in areas where mangroves have been cut down. This makes mangrove forests vitally important to coral reef and commercial fisheries as well.


Coastal protection: The dense root systems of mangrove forests trap sediments flowing down rivers and off the land. This helps stabilizes the coastline and prevents erosion from waves and storms. In areas where mangroves have been cleared, coastal damage from hurricanes and typhoons is much more severe. By filtering out sediments, the forests also protect coral reefs and seagrass meadows from being smothered in sediment