The mangrove is a coastal ecosystem, typical of tropical and subtropical areas. It is the connection point of the marine, terrestrial and fresh water environments.
It originates from the meeting of the fresh water from rivers and the salt water from the seas forming the brackish water, in environments of intense deposition such as bays, estuaries and coastal re-entrances, where the speed of the currents is reduced, favoring the deposition of sediments. During the high tide, when the waters mix and get a higher salt content, there is a change in the pH of the fresh water, causing or favoring the meeting and the concentration of clay particles, silt and organic matter that are usually brought by the rivers and deposited on the river banks, forming a slightly compressed soil, slippery, soft, rich in decaying organic matter and consequently little oxygenated – the oxygen is totally withdrawn by bacteria that use it to decompose the organic matter. The low content of oxygen and salinity variation are features of all these regions, providing the development of unique flora and fauna.
The mangrove contributes to the enrichment of marine water with nutrient salts and organic matter and is among the most responsible for maintaining much of the fishing activities in tropical regions.
Unlike other forests, the mangroves are not rich in species, but are distinguished by the great abundance of populations that live in them. They can be considered one of the most productive natural environments in Brazil. Only three trees constitute the mangrove forest: the red or wild mangrove, the white mangrove and the black mangrove. They present a series of adaptations: respiratory roots, capacity to ultra filter the brackish water and eliminate the salt, and germination in seedlings on the mother plant to be later scattered by the water. The mangrove flora can be increased by a few species such as fern, bromeliads and hibiscus.
The typical vegetation plays an important role as “land fixer” working as a real breakwater, avoiding the siltation of large coastal areas due to its border location between the various environments – sea, river, lakes, land and the architectural structure of its trees – protecting the coastal regions and the watershed against the action of the sea waves, which could trigger erosion. Along the rivers it provides protection against floods, diminishing the force of the flood, preserving arable fields.
As for the fauna, several species of crabs stand out. The oysters, mussels, cockles and barnacles feed by filtering the water. The shrimp also come into the mangroves during the high tide to feed. Many of the fish species of the Brazilian coast depend on the dietary sources on the mangrove forests, at least when they are young. Among them are catfish, bass, ‘manjubas’ and mullets. The richness of fish attracts predators, such as some species of sharks, dogfish and even dolphins.
There are not many typical birds, although some species, like herons and bitterns use mangrove trees as observation, resting and nesting points. These birds feed on fish, crustaceans and mollusks. Among the mammals, the coati, otter and raccoon, or ‘mão pelada’ can be found.
Neglected in the past, the mangrove forest was considered for a long time an inhospitable environment because of the constant presence of black flies, mosquitoes and horse flies. The dark muddy forests, without any aesthetic attractions and infected with harmful insects, made people think, until the mid–70s, that progress of the marine coast meant clean beaches, sanitized landfills, harbors confined by concrete and cultivation experiments to seize the land of old mangroves. Although the economic and social importance is big, this approach was partly responsible for the construction of ports, resorts and coastal highways in these areas, decreasing the extent of mangroves.
Although protected by law, the mangrove forests still suffer from deliberate destruction, domestic and chemical pollution of the water, oil spills and poorly planned landfills.