Vital for healthy coastal ecosystems

Healthy mangrove forests are key to a healthy marine ecology. Fallen leaves and branches from mangroves contribute to the forest detritus and provide nutrients for the marine environment. Intricate food webs of immense varieties of sea life are supported directly through this detritus.

Refuge and nursery grounds

Many threatened and endangered species are native to mangrove forests, which provide critical habitat for diverse marine and terrestrial flora and fauna, such as:

• manatees
• crab-eating monkeys
• fishing cats
• monitor lizards
• sea turtles
• Royal Bengal tigers
• mud-skipper fish

Mangrove forests also provide refuge and nursery grounds for juvenile fish, crabs, shrimps, mollusks, and other invertebrates.

Mangroves are prime nesting and migratory resting and feeding sites for hundreds of bird species. In Belize, there are over 500 species of birds recorded in mangrove areas.

Mangrove Habitat and Growth

Mangrove distribution is primarily determined by sea level and its fluctuations. Other secondary factors are:  air temperature, salinity, ocean currents, storms, shore slope, and soil substrate. Most mangroves live on muddy soils, but they also can grow on sand, peat, and coral rock.

Zonation often characterizes mangrove forests. Certain species occupy particular areas, or niches, within the ecosystem. Some mangrove species occur close to shores, fringing islands, and sheltered bays; others are found further inland, in estuaries influenced by tidal action.

Mangroves vary in height according to species and environment, from mere shrubs to 40 meter (app. 131 feet) tall trees. The prop roots of some mangrove species, such as Rhizophora spp., or red mangrove, and the pneumataphores (unique breathing roots) of others, such as Avicennia spp., or black mangrove, contain many small "breathing" pores, called "lenticels." These allow oxygen to diffuse into the plant and down to the underground roots by means of air space tissue in the cortex, called "aerenchyma." The lenticels are inactive during high tide.

Lenticels in the exposed portions of mangrove roots are highly susceptible to clogging by crude oil and other pollutants, attacks by parasites, and prolonged flooding from artificial dikes or causeways. Over time, environmental stress can kill large numbers of mangrove trees.

Evolutionary adjustments to varying coastal marine environments have produced some astounding biological characteristics within mangrove plant communities. Certain species of mangroves exclude salt from their systems, others actually excrete the salt they take in via their leaves, roots, or branches. In species that exclude salt, the mangrove root system is so effective in filtering out salt that a thirsty traveler could drink fresh water from a cut root, though the tree itself stands in saline soil.

Mangrove Reproduction

Certain mangrove species can propagate successfully in a marine environment because of special adaptations. Embryo germination begins on the tree itself, a process called "viviparity." The tree later drops its developed embryos, called propagules, which may take root in the soil beneath. Viviparity may have evolved as an adaptive mechanism to prepare the propagules for long-distance dispersal, and survival and growth within a harsh saline environment. During this viviparous development, the propagules are nourished on the parent tree, thus accumulating the carbohydrates and other compounds required for later autonomous growth.

Propagules may float for extended periods (depending on the species), up to a year, and still remain viable. Viviparity and the long-lived propagules allow mangrove species to disperse over wide areas.

Mangrove Ecology Workshop Manual (Feller & Sitnik editors, pdf 1.23 MB)

The Mangrove Ecosystem

To understand what constitutes a mangrove wetland, we must understand the intricacies of this quite complex and interconnected ecosystem. Follow the Related Content below to read the important comments by Gilberto Cintron, of the US Fish & Wildlife Service.