World Rainforest Movement

Mangroves and their uncertain future

Mangroves are the coastal equivalent of tropical forests on land. There are various types of mangroves: coastal mangroves, growing without the input of fresh water from inland and that can extend for various kilometres, mangroves growing mainly at the mouths of rivers or deltas, that may be very extensive, and coral reef mangroves that grow on coral reefs above sea level. But they all have something in common, they are very special, fragile and endangered “salt water forests”.

Mangroves are characterised by the woven maze of trees and roots, that are in fact an orderly forest mass, growing in bands according to their differing degree of resistance to periodic flooding by tides and therefore, to salt.

They grow on protected river estuaries and banks in equatorial, tropical and subtropical coastal zones, adapted to tide flow. At high tide, their canopy is barely apparent above the water. At low tide, their respiratory roots are visible, capturing oxygen and transmitting it to the buried roots. This adaptation enables them to survive in soils without oxygen and with a high saline concentration, their leaves also adapt to the scarcity of fresh water and are able to eliminate excess salt.

Mangroves are an irreplaceable and unique ecosystem, hosting incredible biodiversity and among the most productive ecosystems in the world. They house a wide variety of life: migratory birds, marine creatures and reptiles in addition to associated species of flora.

In spite of the fact that at world level there are some twenty species of mangroves, the basic structure of individual mangroves is usually formed by between 3 and 8 species. A wide variety of representatives of the plant kingdom live on them, over 100 fungus, and under them, up to 70 aquatic plants.

The aerial roots of their trees form a web, hosting a multitude of animal species (fish, molluscs, crustaceans) and they operate as zones for mating, refuges and nursery areas for a large number of species, many of them of importance as human food, which has made it possible for populations to settle around them, having their subsistence in resources generated by this ecosystem. Herons, cormorants, eagles and kingfishers find their source of food in mangroves.

When the tide goes down, some mammals approach the beach to eat, such as the wild boar and shrimp-eating monkeys. In the canopy, other primates feed on mangrove leaves and they shelter iguanas, parrots, doves and waders such as spoonbills, ibis, etc. that return to the canopy every night to roost.

Mangroves, in addition to protecting the coasts from erosion caused by hurricanes that periodically scourge these tropical zones, have, for many centuries, provided a multitude of resources to the local population. The most common uses of mangroves and their ecosystems are extraction of firewood, material for housing, and more importantly, fishing and harvesting of sea products, including many crustaceans.

However, thousands of kilometres from this unique ecosystem, so rich in biodiversity, at the tables of the European countries, Japan and the United States, we find the origin of the progressive loss of this balance: consumption of shrimps grown in ponds by the shrimp industry. This consumption has risen over the past years and thousands of hectares of mangroves have been transformed into breeding ponds, where created economic interest is very strong.

The shrimp industry benefits from mangrove conditions to breed shrimps, converting into “ponds” millions of hectares of fundamental habitats for local economies and for biodiversity. Thanks to the support of governments and grants from bodies such as the World Bank and with the support of FAO, today shrimp industries are increasingly being installed in tropical countries.

This activity has disturbed the population living off these ecosystems. Mangroves do not produce enough to support extractive activities by artisan fishers and at the same time the shrimp industry that is considerably undermining the ecosystem’s capacity for production, in most cases, degrading it in an irreversible way. One single company competes with the resources providing subsistence to a population. Over the years, the shrimp ponds drown in their own contamination, and are subsequently abandoned leaving a destroyed ecosystem and local communities impoverished to extreme limits.