Mangrove forests

The term mangrove is used to refer to a group of trees and shrubs that inhabit the coastal intertidal zone. Mangrove forests may also include other associated vegetation such as trees, herbs, and ferns, which are generally found in the upland transitional zone. Mangrove forests are limited to the tropics and subtropics because they cannot withstand freezing conditions and are considered the counterparts of marsh habitats of temperate environments. Mangroves are found bordering the coastline, lagoons, and canals or forming large forests within river deltas. They are especially abundant in areas sheltered from the direct action of waves.

Mangrove trees have developed special morphological and physiological adaptations to cope with the variable flooding and salinity conditions imposed by the coastal environment. Adaptations to withstand flooding include shallow roots to avoid the lack of oxygen in deeper soils and aerial roots, to transport oxygen from the atmosphere to the root system. To cope with varying salinity conditions, different mangrove species have developed different mechanisms to tolerate, exclude or secrete excess salt.

In the U.S. mangrove wetlands are dominated by three main species: the red mangrove (Rhizophora mangle), the black mangrove (Avicennia germinans), and the white mangrove (Languncularia racemosa). The red mangrove often grows in the deepest parts or seaward edge of the coast, while the black and white mangrove species are commonly found in the landward parts of the forest. The red mangrove is generally the dominant species and can be easily distinguished by the formation of a thick root system or aerial roots that rises above the soil and water surfaces.

Due to the influence of tides, most mangroves get flooded at least twice during the day, which facilitates the movement of fish in and out of the wetland. The presence of intricate root systems, fallen branches, wood, and leaves make these wetlands attractive to many different species of fishes and many other organisms that look for food and shelter from predators. Aerial roots of red mangroves are sometimes flooded for long periods of time, allowing crustaceans, sponges, mollusks, and marine vegetation to adhere to the roots and form a rich marine microhabitat. Similarly to marsh habitat, mangroves also provide nursery grounds for aquatic organisms as well as stabilization and protection of the coastline against storms and hurricanes.