Divers chase a sea turtle at the wall break, 12 m deep, San Salvador, Bahamas.
Mangroves, a mandate for the health and vitality of an estimated 22 million hectares of subtropical and tropical coastline ecosystems are increasingly disappearing as a result of human actions and urbanization. Highly adapted to a variable environment, mangroves provide many ecological values, geological structure, and have sustained the livelihoods of indigenous coastal cultures. As resilient as mangrove ecosystems are, these vital forests are being quickly depleted due to human disturbances. Along with their disappearance go the economic resources they provide, the coastal stability they create, the homes for many interdependent organisms that they provide and an alteration of an ecosystem that is irreplaceable.
What is a mangrove?
Brief Biology of Mangroves: What is life like on the edge?
Types of mangrove trees
Adaptability to salinity
Adaptability to water logging
Plant-animal relationships within mangroves
As with most ecosystems, many intricate plant and animal relationships exist. Mangroves provide homes to variety of marine and terrestrial organisms such as oysters, shrimp, fish species, and bird species (pelicans, herons, wood storks, wild flamingos). Many of these organisms, such as in the case of Florida mangroves, are homes to endangered organisms. Mangroves also provide a food source for many organisms within the ecosystems. For example, the coffee bean snail (Melamus coffeus) eats mangrove propagules for subsistence19. Mangroves areas are also dependent on other organisms for pollination, reproduction, and nutrient attainment. Nutrient attainment is generally terrestrial. Many organisms such as ergots and pelicans add nitrogen to the mangrove systems. Additionally, bacteria are found to proliferate throughout the nodules of mangrove leaves. These bacteria are capable of nitrogen fixation. Furthermore, mangrove trees have a close relationship with the soil. The soil surrounding mangrove tree tends to be anoxic with a thin layer of an aerobic zone. NH3 in the soil is oxidized by aerobic bacteria into nitrate ions, which diffuses does through the anoxic layer. Nitrogen (in its various forms) is taken up by the roots, reduced into nitrogen gas or lost to the atmosphere. Some nutrients however are obtained via marine modes. Sponges have been identified as an assistant to nutrient attainment. On some species, sponges grow on the roots, which exchange nitrogen and carbon. The roots of the tree often penetrate through the sponge excessively, these trees have been found to grow ten times faster with the presence of sponges.6
Like many plants, mangroves are dependent on other organisms for pollination. Pollination occurs through the assistance of a variety of organisms depending on the species of tree. Some trees are pollinated by bats, hawk moths, birds, butterflies, bees, small insects, or the wind6. Once fertilization occurs, the embryo of a mangrove is formed through vivpary, which is means the embryo remains on the tree and grows. The root growth is inhibited and the offspring remains on the tree until it is fully developed into a propagule. The offspring or propagules are dispersed by water. They are called seedlings (not a seed or a fruit) and have no ability to resist drying out since water is generally in abundance. Propagules float before establishing roots. In highly saline conditions, these propagules are less likely to settle thus ensuring a adequate environment for growth. One species of mangrove, xylocarpus, commonly know as the cannonball tree has fruits ranging 3 kg.
Importance of mangroves
Mangroves thrive in variable environments and through a series of naturally selecting steps, have adapted to a somewhat harsh environment. Trees in these mangrove systems have developed strategies for reducing the effects of hyper saline conditions through a variety of techniques6. In addition to the variable environment of living along the sea, these habitats are the drainage sites for almost all of the preceding lands. Consequently, any environmental hazard that is exposed to these terrestrial environments drains into mangroves and estuaries. Aside from the typical environmental issues, these habitats are threatened to a greater degree by oil extraction and exploitation as well as by aquaculture and urban development. Until recently, governmental institutions have regarded mangrove ecosystems as wastelands and areas of little economic or cultural value. This terminology designation has therefore caused these habitats to fall victim to over exploitation and resource abuse suffering.
Mangroves in fact are far from wastelands. Mangroves for centuries have provided cultures with many benefits ranging from substance gains to ecosystem diversity. Many indigenous cultures rely solely on mangroves for subsistence fishing and other food resources. In addition to nutrition mangroves provide these cultures with a substantial amount of resources, medicinal drugs, and livelihood. Aside from the human component, mangroves provide geological significance in that they act as a shore stabilizer. In doing so, mangroves provide an area for sediment and carbon deposition. Finally, mangroves provide a wealth of biodiversity and an essential part of the world’s food web.
Mangrove disturbances-the tangled web
Mangroves all over the world have suffered from loss of habitat and contamination. Much of this is due to deforestation for fisheries and contamination from oil spills. Do these same deleterious effects occur in parts of the western hemisphere? What is the state of the mangrove systems in Florida?
Availability of physical data and evidence over time in regard to the status of mangroves is minimal. Many of the trees in Florida suffer from “natural” incidences. Salinity (possibly due to droughts) has been the main source of “natural” mangrove mortality. Mangroves also suffer from increased water turbidity (results in clogging), prolonged flooding, damage by boring organisms, parasitic yellow lichen and wasps. Algal blooms possibly due to nitrogen/agriculture runoff are another source of mangrove mortality. In parts of southern Florida, freshwater flows have been greatly altered due to agricultural runoff and urban engineering of the watershed. This has resulted in changes in the nutrient loads and salinities entering the mangrove systems. Florida mangroves also suffer as much of the world’s mangroves from the “shrimp factory farms.” In Florida, the Shrimp Industry (Tortugas pink shrimp fishery) has increased the loss of habitat for these ecosystems in order to make room for the shrimp pens. Many of these mangroves are harmed due to herbicide and human waste runoff, filling, diking, dredging and oil spills. Of the estimated 430,000-540,000 acres that existed in 1981, about half of this acreage is held by government organizations or non-profit organizations. It is estimated that there is a 5% loss of acreage overall within the state of Florida compared to land estimates of the 19 century. Some areas of Florida however suffer from up to 44% loss of mangrove and wetland acreage19.
Mangroves are unique forests in that they are tolerant to high or variable levels of salinity. In return for this tolerance, mangroves have adapted to this environment through the use of special glands for salt excretion, high tissue tolerance to salt and/or exclusion of salt by aerial roots called pneumatophores6. These aerial roots are in sense the Achilles’ heel for the mangrove forests when it comes to oil exploitation and extraction. Lenticels, which are small circular opening on the mangrove aerial roots, act as breathing organs for mangrove trees. These pores are often clogged as a result of crude oil spills and consequently suffocate the mangrove root system. Death often results from this contamination17. With a loss of the main component of a mangrove forest this ecosystem is damaged. Consequently, the source of shore stability, habitats and sustenance to indigenous cultures are eliminated with the damage cause by oil extraction and use.
Oil pollution can result from leaks in old pipes and gas flare emissions. Much of the crude oil contamination has resulted in mortalities among crabs, fish, and other plant and animal inhabitants. This criss-crossing network of pipelines penetrates through the mangrove systems and often eliminates breeding and feeding grounds for a variety of fish species. Many peoples who subsistence fish go hungry as a result of these excess emissions and contamination17. Although base lined data is limited, it is predicted, based on a few examples that mangrove forests are slow to recover from destruction due to oil spills. These ecosystems are thought to suffer on a long-term basis from oil contaminations. Studies of mangrove systems deaths due to crude oil show the regrowth forests have lower densities, higher seedling mortality, intermittent release of oil through the sediment and open canopies6.
Aquaculture has been around for centuries however the controversy behind current aquaculture and mangroves is one of recent pursuits. Previous sustainable aquaculture practice has existed in “harmony” with mangrove systems. With a 25 percent increase in shrimp demands, shrimp farming has entered into a larger more destructive scale6. Mangroves have suffered the repercussion of deforestation for the purpose of artificial pond construction. As a result, one of the greatest threats to mangrove survival is clear cutting of forests for the purpose of shrimp farm construction. As much as 50 % of mangrove forests have been destroyed for the shrimp-farming endeavors23. With the increase in production demands, artificial ponds cannot be adequately stocked with larvae from the incoming tides. Consequently, aquaculture ponds are being stocked with artificial seeding, the addition of fertilizer and increase in water circulation through the use of pumps. Additionally shrimp farms are supplied with antibiotics and chemical additives6.
Destruction of mangroves through deforestation rather than contamination has its own set of repercussions. Mangroves supply shore stability and consequently can reduce the impact of tropic storms, seawater intrusion on crops and erosion of coastlines. Ironically the destruction of mangroves for shrimp farms decreases the numbers of shrimp larvae and other dependent inhabitants such as the mud crab are evident in areas of deforestation. Depleting mangroves ultimately will decrease the source of shrimp larvae since mangroves act as shrimp nurseries and “an ultimate productivity base.”8. Furthermore, the remains of mangrove deforestation often become acidic and therefore result in decreases in shrimp yield and water quality, and provide plush breeding ground for malaria-ridden mosquitoes6.
Mangrove destruction can also occur indirectly to that of straightforward deforestation. Production and use of “mega” shrimp farms produces excess amounts of effluent. This effluent is composed of chemicals, restricted antibiotics and uneaten shrimp foods. If this effluent is in the correct balance it can lead to an increase in mangrove productivity. However, at levels in which mangrove systems cannot assimilate to, the effluent can lead to disastrous ecosystem results. Examples from Thailand and China, illustrate the devastating effects of a failed shrimp industry where coastlines were left in shambles and excessive effluent altered the ecosystem composition6.
Sixty percent of the world’s population resides along coastal habitats; consequently alteration of such habitat can have devastating environmental and social effects. Mangroves are not only threatened on a daily basis by oil spills, shrimp farms, and governmental oppression but are also, as with many of the earth’s ecosystems are threatened by development. Mangroves suffer from eutrophication, which increases the amounts of nutrients within the sediments of the forest “floors”. This results in an increase in primary production. In excess increases in nutrient production can result in toxic algal blooms, species composition alteration and mangrove death. Sources of eutrophication appear in fertilizer, livestock waste and fossil fuel emission runoff. Typically, mangroves suffer from the common effects of urbanization such as habitat fragmentation and the loss of biodiversity. Deforestation for the sake urbanization often alters the hydrological cycle, creates unstable coastlines and hypersaline farmlands.
Attempts at conserving and stopping the daily destruction of mangrove ecosystems are gaining some momentum. Within the United States various institutions have been initiated. For example, the Estuary Habitat Restoration Council in conjunction with the EPA is working with other “states, tribes and other federal agencies” to address environmental issues in the Gulf of Mexico which is a threatening commercial fishing grounds. They are also working to improve and monitor possible bacterial contamination of mangrove systems. The National Estuary Program has set forth the most common problems facing estuary and mangrove habitats. Each problem is addressed by identifying management approaches to each problem.22 Other agencies and policies have been created in the attempt to conserve the environments such as the creation of the Federal Ocean and Coastal Zone Policies set forth by the Clinton administration. The Clinton administration created the National Marine Sanctuaries Amendment Act of 2000. This act distributes funds for the continued conservation work in the area of National Marine Sanctuaries establishment, management and monitoring. The Coastal Barrier Resource Reauthorization Act of 2000 also set forth by Clinton, helps to preserve costal barrier environments by “prohibiting federal subsidies for development and disaster relief.” Theoretically, if development occurred in this area, federal flood insurance for example would be eliminated in the hopes to discourage development. This act can help to contribute to the lands that are protected. Clinton also signed the Oceans Act of 2000, which establishes a commission on ocean policy. This committee makes recommendations to the President and Congress regarding ocean conservation issues16.
On an international level, the United Nations, in attempt to conserve and manage, is implementing efforts to designate wetland and mangrove areas. Through the United Nation Environmental Programme and with the Integrated Coastal Zone Management, the establishment of Specially Protected Areas is occurring. Initially a 1971 convention to protect “Wetlands of International Importance” occurred in Ramsar, Iran. Since this convention, 100 countries have signed on to protecting certain mangrove and wetland areas, resulting in approximately 830 “Ramsar” sites. (53 million hectares) One third of these wetland areas contain mangroves14. Additionally, grassroots organizations and protests are occurring throughout small villages and communities as illustrated in the Nigerian protests of multinational oil companies.
What can be down to stop the deforestation and contamination of mangrove ecosystems? What can stop the destruction of an environment in which millions of indigenous cultures are dependent upon? Much of the problematic structure to mangrove conservation is the allocation of profits within governmental agencies and economics. For example, Nigerian oil profits, given that they are estimated to be approximately sixty percent of all oil profits, are often misspent and shipped to foreign bank accounts rather than investing in the education, health, ecosystem restoration, social investment or monitoring of environmental regulations within the coutry24. Government and oppressive military institutions fail to see the economic value in long-term sustainability of the mangrove systems. Governments need to hold oil companies accountable for environmental exploitation and enforce environmental monitoring standards. Furthermore, Oil companies have the responsibility to at least meet the environmental standards held in homeland countries. Multinational oil companies also need to provide compensation for both resource depletion and for the production of pollutants to the local communities. As seen throughout many environmental issues, securing the land rights of the local communities lends itself to the creation of a sustainable environment. Governments that ignore landholder’s rights and pawn off land to moneymaking corporations are not benefiting the economic stability of the country in the long-term view. Finally, economics is driven by consumer demands. Consequently, consumers hold the power to control or monitor the behavior of multinational corporations.
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Mangrove Action Project
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25http://www.foodfirst.org Farming Shrimp, Harvesting Hunger: The costs and benefits of the Blue
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