Key Points

• Mangroves worldwide cover an approximate area of 240 000 square kilometers of sheltered coastlines in the tropics and subtropics.
• Four of the most common ecotypes include fringe, riverine, basin, and scrub forests.
• Mangroves are restricted to the intertidal zone.
• Mangroves in general have a great capacity to recover from major natural disturbances.
• Mangroves maintain water quality by trapping sediments and taking up excess nutrients from the water.

Prop roots of the red mangrove (Rhizophora mangle) tree create thickets that harbor a wide variety of creatures both above and below the water. Credit: NPS.

Mangrove Classification

Ecologically, mangroves are defined as an assemblage of tropical trees and shrubs that inhabit the coastal intertidal zone. A mangrove community is composed of plant species whose special adaptations allow them to survive the variable flooding and salinity stress conditions imposed by the coastal environment. Therefore, mangroves are defined by their ecology rather than their taxonomy. From a total of approximately 20 plant families containing mangrove species worldwide, only two, Pellicieraceae and Avicenniaceae, are comprised exclusively of mangroves. In the family Rhizophoraceae, for example, only four of its sixteen genera live in mangrove ecosystems.

Mangrove Distribution and Physical Description

Mangroves worldwide cover an approximate area of 240 000 km² of sheltered coastlines. They are distributed within the tropics and subtropics, reaching their maximum development between 25N and 25S. Their latitudinal distribution is mainly restricted by temperature since perennial mangrove species generally cannot withstand freezing conditions. As a result, mangroves and grass-dominated marshes in middle and high latitudes fill a similar ecological niche.

The global distribution of mangroves is divided into two hemispheres: the Atlantic East Pacific and the Indo West Pacific. The Atlantic East Pacific has fewer species than the Indo West Pacific (12 compared to 58 species, respectively). Species composition is also very different between the two hemispheres. Out of a total of approximately 70 mangrove species, only one, the mangrove fern, is common to both hemispheres.

In the continental United States, mangroves are mainly distributed along the Atlantic and Gulf coasts of Florida. They also occur in Puerto Rico, the U.S. Virgin Islands, Hawaii, and the Pacific Trust Territories. Craighead (1971) estimated a coverage of approximately 1,750 km² of mangroves along the Florida coast, with the highest development along the southwest coast. The Gulf of Mexico and Caribbean regions are characterized by low species richness, with only four dominant species: Rhizophora mangle (red mangrove), Avicennia germinans (black mangrove), Laguncularia racemosa (white mangrove), and Conocarpus erectus (button-mangrove or buttonwood). Black mangroves, however, can be found as far north as Texas, Louisiana, and Mississippi, indicating this species’ greater tolerance to low temperatures and its ability to recover from freeze damage.

The California Current, which limits the northern extent of mangroves along the Pacific coast of the Americas, brings cold water as far south as Baja California. At the southern tip of this peninsula, mangroves are represented by an occasional, scrubby black or white mangrove. The mangroves of the Pacific Islands are represented by a very different assemblage of species belonging to the Australasian group. Some of the more characteristic genera include Bruguiera, Rhizophora, Avicennia, Sonneratia, and Ceriops. [READ MORE]