Species Description: Mangrove swamps dominate much of the world's tropical and sub-tropical coastlines, and have a similar distribution pattern as coral reefs. There are approximately 35 species of true mangroves and another 60 or more species of mangrove associates. Most species occur throughout the Indo-Pacific region, with three commonly occurring in the Americas.
Rhizophora mangle, the red mangrove, is a subtropical/tropical tree which colonizes coastlines and brackish water habitats below the 20 ºC isotherm in both the northern and southern hemispheres. Red mangrove trees dominate the Atlantic and Gulf coasts of the United States to about 28ºN latitude, after which a zone of transition to salt marshes occurs. Red mangroves generally are found closest to the water's edge and are distinguished easily from other mangroves by their prominent prop roots which extend into the water from higher up on the stem of the plant. Red mangroves have leaves which are somewhat larger and shinier than those of other mangroves. They are further distinguished by their fruits, or propagules, which are long and pencil-shaped. While these may resemble seed pods, they are actually embryonic root structures.
Regional Occurrence: Rhizophora mangle occurs worldwide in coastal and estuarine areas of the tropics and subtropics to about 28° in both the northern and southern hemispheres.
IRL Distribution: In the Indian River Lagoon, red mangroves are common landscape features to approximately 28° North, around the vicinity of Merritt Island. North of this location is the transition zone where mangrove forests gradually give way to salt marshes. Frost stress north of the transition zone prevents red mangroves from becoming established.
Age, Size, Lifespan: Little is known regarding typical age to maturation in mangroves in south Florida, though it has been hypothesized that maturation age for mangroves in Florida is in some way linked to the periodicity of hurricanes.
Abundance: Red mangroves are generally the dominant species of mangrove at or immediately adjacent to the water line, though they may often occur with black mangroves and white mangroves.
Dispersal: Propagules of the red mangrove detach from the parent tree upon ripening and may float in salt water for approximately one year without rooting.
Reproduction: Rhizophora mangle flowers are thought to be self pollinated or wind pollinated. Following fertilization, mangrove propagules undergo continuous development from flower to germinated seedling while still attached to the parent plant, with no dormant or seed phase, thus exhibiting vivipary. The seedlings, or propagules, eventually fall from the parent plant and are able, in the absence of suitable substrata, to float for extended periods (over a year) in salt water without rooting.
Temperature: The geographic range of R. mangle generally matches the 20 °C isotherm in both the northern and southern hemispheres, and is similar to the range of coral reefs. Frost stress beyond 28° north and south latitudes prevents red mangroves from becoming well established. However, when subjected to cold stress, populations of red mangroves show differences in survival rate and amount of damage done per plant based on their geographic points of origin.
Salinity: As facultative halophytes, mangroves have the ability to thrive in waterlogged soils which may have salinities ranging from 0 - 90 ppt. Mangroves exhibit several different types of mechanisms for coping with highly saline conditions. Rhizophora mangle excludes the salt in seawater at the root-substratum interface. The black mangrove (Avicennia germinans) and the white mangrove (Laguncularia racemosa) are able to take up seawater through their roots, but they excrete excess salt through pores, or salt glands, located on the surface of leaves.
Other Physical Tolerances: Mangroves can experience reducing conditions to at least -200 mV. One of the most visibly obvious adaptations to anoxia are root adaptations. R. mangle utilizes prop roots which grow downwards from the stem of the plant, rather than relying on roots growing upwards from the substrate. Lenticels, or pores, in the aerial roots are presumed to be the path through which oxygen is supplied to the underground root system. Fine lateral rootlets are able to accumulate in the substratum, and produce most of the underlying peat on which mangrove swamps are built. Adaptations to extremes in pH have not been examined in the red mangrove, however, pH values between 5.3 and 7.8 have been reported.
Trophic Mode: Mangrove forests typically show a wide range of productivity, depending on factors such as hydrological regimes, nutrient supply, etc., and are considered to be vital sources of organic matter for estuarine systems.
Competitors: Ball (1980) suggested that competition among the three mangrove species may be partially responsible for the zonation observed in many mangrove areas.
Direct consumers of mangrove propagules in Florida include the spotted mangrove crab (Goniosis cruentata), the mangrove land crab (Ucides cordatus), the coffee bean snail (Malampus coffeus) and the ladder horn snail (Cerithidea scalariformis).
Consumers of mangrove leaves include the mangrove crab (Aratus pisonii), the spotted mangrove crab (G. cruentata), the blue land crab (Cardisoma guanhumi), and various types of insects. Wood boring isopods feed upon and damage prop roots.
Habitat: Red mangrove propagules may float for upwards of a year without taking root. They generally take root upon coming to rest on a suitable substrate area consisting of sand, silt, mud or clay which offers some protection from waves. Propagules may root even while completely submerged; and mature trees, depending on type, tend not to be sensitive to hydroperiod; they may remain submerged anywhere from several hours to nearly permanently without showing adverse effects.
Associated Species: Mangroves form intertidal forests in which red mangrove prop roots, black mangrove pneumatophores, and their associated peat banks serve as the dominant intertidal substrata for other members of the mangrove community. Black mangroves (Avicennia germinans) and white mangroves (Laguncularia racemosa) are usually found in association with red mangroves. Segregation of the three species does occur, however, with red mangroves typically occupying the lowest intertidal position. Black and white mangroves occur at slightly higher tidal elevations.
Special Status: Habitat structure
Benefit in the IRL: Mangrove forest ecosystems are vital as sources of energy and provide nursery habitat for juvenile fish, and invertebrates. They also provide roosting and nesting habitat for wading birds. Additionally, they are a source for timber production and are important as buffers in decreasing storm impacts along coastlines.
Economic Importance: Because of their vital role in providing nursery habitat for juvenile fish, many of which are commercially or recreationally important, mangroves contribute to the continuing success of Florida's tourism and fishing industries.
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