Mangrove

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Image:Mangroves.jpg Mangrove are woody trees or shrubs that grow in coastal habitats or mangal (Hogarth, 1999), for which the term mangrove swamp also would apply. Mangrove plants are found in depositional coastal environments where fine sediments, often with high organic content collect in areas protected from high energy wave action.

Mangrove plants are a diverse group which have been able to exploit a habitat (the intertidal zone) because they have developed a set of physiological adaptations to overcome the problems of anoxia, salinity and frequent inundation. Each species has its own capabilities and solutions to these problems and this may be the primary reason why on some shorelines mangrove tree species show distinct zonation as a consequence of variations in the range of environmental conditions across the intertidal zone. The mix of species at any location within the intertidal zone is therefore partly determined by the tolerances of individual species to physical conditions such as tidal inundation and salinity, but also may be influenced by other factors such as predation of their seedlings by crabs.

Image:Mangroves1.JPG Once established, the roots of the mangrove plants help to impede water flow and thereby enhance the deposition of sediment in areas where it is already occurring. It is usually the case that the fine, anoxic sediments under mangroves act as sinks for a variety of heavy (trace) metals which are scavenged from the overlying seawater by colloidal particles in the sediments. In areas of the world where mangroves have been removed for development purposes, the disturbance of these underlying sediments often creates problems of trace metal contamination of seawater and biota.

It is often stated that mangroves provide significant value in the coastal zone as a buffer against erosion, storm surge and tsunamis. While there is some attentuation of wave heights and energy as seawater passes through mangrove stands, it must be recognised that these trees typically inhabit areas of coastline where low wave energies are the norm. Therefore their capacity to ameliorate high energy events like storm surge and tsunamis is limited. Their long term impact on rates of erosion is also likely to be limited. Many river channels that wind through mangrove areas are actively eroding stands of mangroves on the outer sides of all the river bends, just as new stands of mangroves are appearing on the inner sides of these same bends where sediment is accreting.

They also provide habitats for wildlife, including several commercially important species of fish and crustacea and in at least some cases export of carbon fixed in mangroves is important in coastal foodwebs. In Vietnam, Thailand, the Philippines, and India, mangrove plantations are grown in coastal regions for the benefits they provide to coastal fisheries and other uses. Despite replanting programs, over half the world's mangroves have been lost.

The mangal is often considered a type of biome. Mangrove habitat is exclusively subtropical and tropical and tidal, and therefore having soil or sediment that is water-logged and saline or of variable salinity. Areas where mangal occurs includes estuaries and marine shorelines. A wide variety of plant species can be found in mangrove habitat, but some 54 species in 20 genera, belonging to 16 families constitute the "true mangroves", species that occur almost exclusively in mangrove habitats and rarely elsewhere (Hogarth, 1999).

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Mangroves in the United States

Because of their sensitivity to sub-freezing temperatures, mangroves in the continental United States are limited to the coastal Florida Peninsula from Cape Canaveral on the east around the keys and up to Tampa Bay on the west. The mangal of the Banana and Indian Rivers of Brevard County and within the confines of the Kennedy Space Center is significant.

Around the entrance to Port Everglades in Fort Lauderdale are several stands of a formerly much more extensive covering of mangroves. Miami Dade County's Biscayne Bay was formerly extensively fringed in mangroves. Most of these have been attrited by development down to isolated stands, however the Oleta River, an estuary in northern Miami Dade County has a rather large mangal that is still relatively intact and is now a state recreation area. Southern Biscayne Bay and Card Sound have extensive fringing mangroves intact, as do the lee side of most of the Florida Keys.

The southern tip of the Florida Peninsula is the largest intact mangal in the continental United States. It comprises the whole southern part of the Everglades National Park. This habitat extends from Card Sound in the west across the southern part of Miami Dade County into Monroe and Collier Counties, including the Cape Sable area and the Ten Thousand Islands in the west. Included in this community are several almost exclusively mangrove habitat islets scattered across Florida Bay.

The Keys and Everglades mangrove community is critical as a nursery for the commercially important Keys shrimp industry. Other important species that breed or live part of their life cycle in this habitat are the tarpon, snook, lemon shark, nurse shark, snapper, spiny lobster, trout, and bonefish. It is also the exclusive habitat of the american crocodile.

There are several scattered stands of mangrove on the west coast of Florida. The estuaries of the Calusahatchee River and Charlotte Harbor. Like their counterparts on the east coast, they were formerly much more extensive, but have been attritted by development. Sarasota Bay, Lemon Bay, Anna Maria Bay, and the estuary of the Manatee River also possess sigificant mangrove growth. Tampa Bay's mangroves have been likewise relagated into small isolated stands.

Image:Mangrove knees Yap.jpg

1 Mangroves in the United States
2 Species of mangroves
- 2.1 Major components
- 2.2 Minor components
3 Mangroves in other media
4 See also
5 References
6 External links

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Species of mangroves

The following listing (modified from Tomlinson, 1986) gives the number of species of mangroves in each listed plant genus and family.

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Major components

Family	Genus, number of species
Acanthaceae<ref name=Acanthaceae>Also known as Avicenniaceae or Verbenaceae.</ref>	Avicennia, 9
Combretaceae	Laguncularia, 11; Lumnitzera, 2
Arecaceae	Nypa, 1
Rhizophoraceae	Bruguiera, 6; Ceriops, 2; Kandelia, 1; Rhizophora, 8
Sonneratiaceae	Sonneratia, 5

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Minor components

Family	Genus, number of species
Acanthaceae<ref name=Acanthaceae/>	Acanthus, 1; Bravaisia, 2
Bombacaceae	Camptostemon, 2
Cyperaceae	Fimbristylis, 1
Euphorbiaceae	Excoecaria, 2
Lythraceae	Pemphis, 1
Meliaceae	Xylocarpus, 2
Myrsinaceae	Aegiceras, 2
Myrtaceae	Osbornia, 1
Pellicieraceae	Pelliciera, 1
Plumbaginaceae	Aegialitis, 2
Pteridaceae	Acrostichum, 3
Rubiaceae	Scyphiphora, 1
Sterculiaceae	Heritiera, 3

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Mangroves in other media

The mangrove is used as a symbol in Annie Dillard's essay Sojourner due to its significance as a self-sustaining biome.

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References

Hogarth, Peter J., 1999: The Biology of Mangroves, Oxford University Press (ISBN 0198502222).
Thanikaimoni, G., 1986: Mangrove Palynology, UNDP/UNESCO and the French Institute of Pondicherry, ISSN 0073-8336 (E).
Tomlinson, P. B., 1986: The Botany of Mangroves, Cambridge University Press.
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