Mangrove Ecosystems

There are about 60 species of mangrove trees belonging to several botanical families. In the Americas, there are eight species of mangroves, in the orient about 40 species, and in Africa 13 species (Tomlinson 1986).

At low tide, most of the trees in the ecosystem, like red mangroves (left) and white mangroves (right) are out of the seawater. During high tide, the aerial roots are submerged.

A large area of black mangroves at Balandra lagoon (Baja California Sur, Mexico) at high tide. Most of the sediment surface is covered by 10-20 cm seawater. At the front, salt-tolerant Salicornia bushes, proposed as a crop plant for future seawater agriculture by CIB scientists.

The sediment of a mangrove ecosystem is anaerobic (lacking oxygen). Therefore, the black mangrove tree is breathing and adsorbing minerals through 10-15 cm-long aerial roots. At high tide these aerial roots are submerged.

Mangroves grow in shallow coastal lagoons (average depth 0 to 2 m) where they are protected from wave action, strong winds, and tidal currents. The soil is composed of thick organic matter mixed with sediment and is anaerobic except for the soil surface.

Many times, tropical mangrove ecosystems are located in estuaries, where seawater and fresh river water mix, but mangroves can also proliferate in semiarid areas where they have limited or no access to freshwater.

Most mangrove ecosystems (back side) are connected to the coastal waters (front side) through a relatively narrow and shallow channel (2-50 m wide). All the water exchange of the lagoon and the entire livelihood of this complex ecosystem depend on this small channel. Blocking the channel, as done occasionally, can fast destroy the entire ecosystem.

Despite the arid environment of Baja California Sur (Mexico), the mangrove forest is proliferating. The growth is so dense that small islands and sandbars (like this one in La Paz bay) in the coastal lagoons are completely covered by a "jungle-type" vegetation.