Mangrove Ecology of Florida and the Caribbean

This topic submitted by Max Myers ( myersml81@hotmail.com) at 12:56 AM on 6/14/03.

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Mangroves are a group of evergreen trees/shrubs found in swamps and forests along the coastal areas in tropical and subtropical areas between 25 degrees north and 25 degrees south latitude. Mangroves make up 75% of the coastal vegetation in the tropical and subtropical regions of the world (Dawes). The mangrove forests are an essential component of the tropical and subtropical coastlines for many reasons. The forests acts as an intermediary between the open ocean and the coast helping to prevent erosion, filter nutrients, and provide protection from sever weather. Mangrove forests also form an incredibly diverse and complex habitat, which includes nursery grounds for fish/marine invertebrates, offer shelter for a variety of organisms, and are nesting areas for coastal birds. The mangroves and the ecosystem they create also have many uses for humans, but have tragically been exploited like so many other resources. Human impact on the mangrove ecosystem with out consideration for the impact loss of mangroves has on the local environment is not an uncommon event. Mangroves are critically linked to the health of the coastal/marine environment and it is important to understand their function as well as the impact of humans on the mangrove environment.

In Florida there is close to half a million acres of mangroves that cover the coast and create an ecosystem that is essential to the overall health of the coastal community (Florida). Mangroves are unique plants because they thrive in relatively adverse conditions. Mangroves must deal with high levels of salt in the water, anaerobic soil, withstand waves breaking against the shore, and tolerate times when roots are completely exposed to the air during low tide or completely submerged during high. These organisms are halophytes, or salt loving, but do not require salt water to survive (nhmi.org). It is believed that Mangroves have adapted to thrive in saltwater as a way to reduce competition among other plants. (Kuenzler 352). In southern Florida and the Caribbean there are three species of mangroves that dominate the coasts; Red mangroves, Rhizophora mangle, Black mangroves, Avicennia germinant, and White mangroves, Laguncularia racemosa. There is a general zonation pattern of the mangrove species in Florida and the Caribbean. Red Mangroves are found near the low tide mark and dominate the part of the coast that is most often affected by the tides, the black mangrove is abundant around areas where high tide reaches and the white mangrove is the furthest inland (Kuenzler). Each species has different morphological characteristics that help them to thrive in their environment. Rhizophora has characteristic prop roots, or stilt roots, which grow from the trunk and drop roots which stem from the branches (nhmi.org). The prop roots and drop roots serve to support the red mangrove in the loose soil and aid in respiration because much of the time these roots are exposed to the air (mangroves.nus). The prop roots contain pores called lenticels which allow oxygen from the air to diffuse into the plant. Rhizophora also has characteristic dark green leaves that come to a point at the end. Avicennia has a root system that consists of a series of pneumatophores, a type of aerial root, which grow up from roots growing laterally in the soil and then grow up and out of the water (nhmi.org). Because the soil in mangrove habitats is generally anaerobic the pneumatophores are advantages for respiration. Avicennia also has a layer of salty residue on the underside of its leaves. Glands in the leaves secret the salt and regulate salt levels in the plant. Laguncularia is most commonly found further inland and unlike the other mangrove species found in Florida and the Caribbean the white mangrove does not have a system of specialized roots, such as prop roots or pneumatophores. Laguncularia does have two glands at the base of each leaves which secret salt. These glands serve a regulatory function similar to the glands on the leaves of the black mangrove.

The mangroves location around coastal areas and in estuaries combined with their unique root systems has provided a habitat for a variety of organisms. Coastal birds such as pelicans, spoonbills, and osprey use the mangroves as a nesting site and the mangroves are home to many food sources for the birds (nhmi.org). In the waters around the mangrove roots, especially the prop roots of the red mangrove, a variety of juvenile game fish can be found. Algae and marine invertebrates such as sponges, corals, and anemone can be found attached to prop roots while clams, sea snails, shrimp, and other organisms use the mangroves for shelter and a feeding ground. The mangroves are the key to major food webs in the coastal community. Researchers in the 1960’s found that mangrove leaf litter is the basis for a food chain that links the entire coastal community (mangrove.org). Mangrove leaves that fall into the water are later consumed by fungi and other decomposers which are a source of food for various detritivors, such as snails and mollusks. These consumers are then eaten by secondary consumers such as small fish and crabs, and finally birds and game fish consume the smaller organisms (mangrove.org)

As crucial as mangroves are as a habitat and member of a food chain they are as equally important to the physical landscape of the coast. The root systems of the mangroves and their overall abundance are crucial to prevent erosion from waves by absorbing the impact of the waves and preventing the soil from being carried into the ocean. If the coast is eroded to much the surrounding waters could be subject to siltation which has damaging effects like the production of algae blooms. During hurricane season mangroves are vital to preserving the coast form even greater damage had the mangroves not been there to absorb the impact of the waves (Kuenzler). Without the mangroves protecting coastlines erosion would destroy the coast sweeping the soil into the ocean and later affecting the open waters.

Mangroves help to protect the coast and thus human settlements but they also have been utilized by humans in a variety of other ways. The trees themselves have been used as fuel, fire wood, timber, and even food. In coastal communities of previous centuries the mangroves were an essential source of timber for boats, homes, and other supplies (Macintosh).
The habitats the mangroves create have been utilized as fisheries, shrimp farms, and other forms of aquaculture (Macintosh). Some estimates say that 90% of commercial fish and 75% of game fish utilize the mangroves at some point in their lives (mangrove.org). Today sport and commercial fisherman rely on the preservation of mangroves to protect the quality of the fish in the open waters (Kuenzler). In more recent years mangrove swamps have been altered for the purposed of aquaculture such as shrimp farming. Shrimp farming can be devastating to the mangrove community because juvenile fish and invertebrates are displaced and pollution of the water increases (Macintosh). In the case of most aquacultural ventures making money is the main motivation and adverse environmental affects are not necessarily considered.

Other than exploiting the mangrove resources, mangrove forests have been completely cleared for urban development. Often mangroves are destroyed with out considering how essential they might be to the ecosystem. Human appraisals of mangrove forests have, in the past, resulted in the mangroves being considered equivalent to a wasteland (Kuenzler). In Florida and the Caribbean mangroves were first used by settlers for fuel and today mangrove habitat is cleared for urban development, specifically relating to beach front property and tourism (Macintosh). In Puerto Rico one-third of the original area occupied by mangroves has been destroyed as a result of development and other human actions (Kuenzler). Although the human impact on mangrove communities in Florida and the Caribbean is severe there is still a chance to preserve what is left. Further development of the coast must be prevented and legislative action is necessary to conserve the remaining mangrove environments.

Mangroves are a unique species of plant that are the scaffolding on which an entire ecosystem is built. The value of the mangroves to humans, to other organisms, and to the physical landscape of the coast can not be given a price tag. It is important to understand why the mangrove community is so important and to take steps to preserve what is left.

References:

Dawes, Clinton. Katherine Siar & Donald Marlett. “Mangrove structure, litter and
macroalgal productivity in a northern-most forest of Florida.” Mangroves and Salt Marshes 3: 259–267. Kluwer Academic Publishers. 1999.

Kovacs, John Michael. “Assessing mangrove use at the local scale”. Landscape and
Urban Planning.43 (1999): 201-208.

Kuenzler, Edward J. “Mangrove Swamp Systems.” Coastal Ecological Systems of the
United States. 347-371. Editors: Odom, Copeland, and McMahon. The
Conservation Foundation 1974.

Macintosh, D. and S. Zisman. “The Status of Mangrove Ecosystems: Trends in the
Utilisation and Management of Mangrove Resources.” October 1999.

Ronnback, Patrick. “The ecological basis for economic value of seafood production
supported by mangrove ecosystems.” Ecological Economics. 29 (1999): 235-252.

Rutzler, Klaus. and Ilka C. Feller. “Caribbean Mnagrove Swamps.” Scientific
American. 94-99. March 1996.


Internet Sources:

Department of Environmental Protection, Florida Marine Research Institute. http://www.dep.state.fl.us/coastal/habitats/mangroves.htm

Mangrove Action Project. http://www.earthisland.org/map/mngec.htm

Mangrove Replenishment Inititive. www.mangrove.org

Mangroves. http://www.nhmi.org/mangroves/index.htm. .

“What Are Mangroves” Department of Natural Resources Bureau of Marine
Research. Pamphlet. P.O. Box F St. Petersburg, FL 337. 1985. http://darter.ocps.net/classroom/klenk/FT/manginf.html


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