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Mangrove Ecosystems: Definitions, Distribution, Zonation, Forest Structure, Trophic Structure, and Ecological Significance
By Karen L. McKee

Definitions
The term “mangrove” refers to an assemblage of tropical trees and shrubs that grows in the intertidal zone. Mangroves include approximately 16 families and 40 to 50 species (depending on classification). According to Tomlinson (1986), the following criteria are required for a species to be designated a “true or strict mangrove”:

1. Complete fidelity to the mangrove environment.
2. Plays a major role in the structure of the community and has the ability to form pure stands.
3. Morphological specialization for adaptation to the habitat.
4. Physiological specialization for adaptation to their habitat.
5. Taxonomic isolation from terrestrial relatives.

Thus, mangrove is a non-taxonomic term used to describe a diverse group of plants that are all adapted to a wet, saline habitat. Mangrove may typically refer to an individual species. Terms such as mangrove community, mangrove ecosystem, mangrove forest, mangrove swamp, and mangal are used interchangeably to describe the entire mangrove community.

Distribution

Mangrove distribution is circumglobal with the majority of populations occurring between the latitudes of 30° N and S (Tomlinson 1986). At one time, 75% of the world’s tropical coastlines was dominated by mangroves. Unfortunately, mangrove extent has been significantly reduced due to human activities in the coastal zone. There are two centers of mangrove diversity: the Eastern group (Australia, Southeast Asia, India, East Africa, and the Western Pacific) where the total number of species is approximately 40 and the Western group (West Africa, Caribbean, Florida, Atlantic South America, and Pacific North and South America) where the number of species is only 8. Thus, New World forests are relatively depauperate compared to Old World forests.

In Belize, there are three true mangrove species: Rhizophora mangle (red), Avicennia germinans (black), and Laguncularia racemosa (white). A fourth species, Conocarpus erectus, is an important mangrove associate in Belize that is transitional between the true mangroves and non-mangrove species. At first glance, these species may appear very similar, but closer inspection reveals differences in morphology, physiology, and reproductive biology. These species can be distinguished using characteristics such as growth form, bark, and structure of leaves, twigs, aerial roots, flowers, and fruits/ propagules.

Reproductive Strategies

Mangroves have little capacity for vegetative propagation and are thus dependent on seedlings for forest maintenance and spread (Tomlinson 1986). Although some species (A. germinans and L. racemosa) can resprout from stumps (coppicing), this process is not equivalent to propagation. Mangroves exhibit two relatively unique reproductive strategies: hydrochory and vivipary (Tomlinson 1986; Rabinowitz 1978).

Hydrochory (dispersal by water) is a major means which mangrove spreads seeds, fruit, and/or propagules. Tidal action can carry mangrove diaspores great distances from their point of origin. Vivipary refers to the condition in which the mangrove embryo germinates while still attached to the parent tree. A number of mangrove species, including R. mangle, for example, may remain attached to the parent tree for 4 to 6 months and attain lengths of 25 to 35 cm at “maturity,” they fall to the ground or into the water where they are dispersed by the tides. The embryo of A. germinans breaks through the seed coat but remains enclosed in the fruit wall until detachment. Upon falling into the water, the thin pericarp is quickly shed, leaving the seedling, which is composed of two folded cotyledons. Laguncularia racemosa is not considered to be viviparous, but germination often occurs during dispersal. Vivipary increases the chances of successful establishment in an unpredictable environment where germination of seeds would typically be inhibited.

Source :
MANGROVE ECOLOGY WORKSHOP MANUAL
Edited by IIka C. Feller & Marsha Sitnik

mangrove mangrove

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