Man in the Mangrove: Is life on the edge slipping off? (final)

This topic submitted by Krista Holman ( KEHolman@Hotmail.com) at 1:31 PM on 6/7/02.

Students hard at work on the "Mangrove Challenge"! (Sierpe River, SW Costa Rica)

Tropical Field Courses -Western Program-Miami University

Man in the Mangrove
Is Life on the Edge Slipping off?

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?

Mangroves are maritime woody trees and shrubs that line the coasts of tropical lands. Mangroves supply coastal stability and habitats for a large portion of marine life. Mangrove systems are well adapted to a variable environment due to the influx of saline waters and waterlogged soils. Living in such a variable or even harsh environment places a mangrove ecosystem in an environment in which survival is a huge obstacle to overcome. Mangrove systems in addition to natural obstacles, such as hurricanes and erosion, face additional obstacles created by humans in the form of super fisheries, oil spills and development. In order to understand the threats faced by mangroves, analysis of the biology mangrove system must be fully understood.

Brief Biology of Mangroves: What is life like on the edge?

Types of mangrove trees

The foundation of a mangrove ecosystem lies in the species of mangrove trees. Although mangroves ecosystems are thought to be composed of anywhere from 50Ð60 species of mangroves trees, most of these species can be classified into two main families: Avicenniaceae and Rhizophoraceae. More generally mangroves are classified into red, black or white mangrove trees. Red mangroves tend to grow well in mudflats, ranging from 1.5 feet into the intertidal zone. Black mangrove trees tend to grow at levels where the high tide covers the root systems and low tides expose roots. White mangroves tend to be present at extended distances from the water. Biomass tends to increase from white to black to red. Mangroves are the second highest source of primary production next to rainforests6. Mangrove productivty is influenced by species composition, age, competition, substrate, wave action, bird action and hurricanes19. What is the difference in mangrove trees? Aside from basic species differentiation (leaf structure, root structure, reproduction), mangroves tend to differ in their location dependent on species identification. Since red mangroves are closer to the water, decomposition occurs at a greater rate due to the shredding action of craps and amphipods. Red mangroves also produce the highest detritus, which is a food source for many organisms. The peat produced by mangroves increases the acidity of the surrounding area. This action tends to dissolve limestone bedrock and eventually, through microbial activity, produces the characteristic sulfur smell found in mangroves19. Additionally, since red mangrove trees are present in areas of increased wave and tidal fluctuation there is a amount of decomposition.

Adaptability to salinity

Living on the edge of freshwater and saltwater environments creates a huge obstacle for mangrove ecosystems in salinity adaptation. Mangroves tend to have three main methods of dealing with variable and high salinities: exclusion, secretion, and accumulation. Exclusion involves the blockage of salt water through the hydrophobic action of the lenticels. Lenticels on mangroves aides in increasing levels of air exposure but they also tend to close during high tides (when trees are exposed to saltwater) and open during low tides in order to take in CO2. The second method of salinity adaptation is that of secretion. Dependent on the species of tree, salt can be secreted at different locations on the plant. Salt is often secreted in the bark of stems and roots. Salt can also be secreted on the leaves of some groups such as Acicennia, which gives the leaves a salty flavor. Other groups of mangrove trees produce hairs on the lower leaf surface, which drip salt. These plant parts are essential to decrease the deleterious effects of salt. This is evident in an increase of root to shoot ratio as salinity increases. The final method of dealing with variable/high salinities is accumulation. Many mangroves trees have salt glands, which are packed full of mitochondria. An increase in surface area within the mitochondria results in a higher metabolic rate for salt degradation. Many species also have tissues that are tolerant to high levels of salt. Often many species can deal with extremely high levels of salinity rather than extremely variable salinity conditions6.

Adaptability to water logging

Mangroves live in a dynamic environment where water levels vary from floods to drought like conditions. How do mangroves conquer times of water logging and low aeration? One ÒcureÓ for this harsh environment is the action of the lenticels. Since lenticels are hydrophobic they close during high tides, which reduced the intake of water. When tides recede, the lenticels open to take in CO2. The more ÒfamousÓ method of dealing with the possibility of drowning is the presence of aerial roots. Aerial roots are not highly embedded in the soil and consequently exposed more to the atmosphere than typical root systems. These roots also contain aerenchyma tissue, which is shaped like a honeycomb. This tissue diffuses air through the large gaps and transport throughout the rest of the tree. Aerial roots can be up to 2 meters above ground and can make up a large portion of the above ground biomass6. Another adaptive structure utilized by mangrove trees is the production of pneumatophores. Pneumatophores are extensions of the root system that have a high amount of lenticels plastered throughout the extension. These ÒappendagesÓ stretch out above the ground in order to increase the amount of aeration of the tree. In addition to this plethora of adaptations, mangrove trees also utilize the position of leaves to reduce water loss. Photosynthesis occurs to assimilate CO2 at the expense of H2O. Consequently, many mangrove trees are threatened by the lack of unsaliniated water. These trees therefore have a tendency to angle their leaves to decrease leaf temperature and therefore evaporation of water. This angle alignment increases as salinity levels increase1.

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 worldÕs 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?

Florida mangroves
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 ÒnaturalÓ incidences. Salinity (possibly due to droughts) has been the main source of ÒnaturalÓ 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 worldÕs mangroves from the Òshrimp factory farms.Ó 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.

Oil effects
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 AchillesÕ 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.

Fisheries
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 ÒharmonyÓ 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 Òan ultimate productivity base.Ó8. 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 ÒmegaÓ 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 worldÕs 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 earthÕs ecosystems are threatened by development. Mangroves suffer from eutrophication, which increases the amounts of nutrients within the sediments of the forest ÒfloorsÓ. 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 Òstates, tribes and other federal agenciesÓ 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 Òprohibiting federal subsidies for development and disaster relief.Ó 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 ÒWetlands of International ImportanceÓ occurred in Ramsar, Iran. Since this convention, 100 countries have signed on to protecting certain mangrove and wetland areas, resulting in approximately 830 ÒRamsarÓ 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 landholderÕs 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.

Sources
1Adam, P. 1993. Saltmarsh Ecology. Cambridge University Press.

2Alongi, Daniel. 1998. Coastal Ecosystem Processes. CRC Press.

3Aube, M., and Caron, L. 2001. The mangroves of the north coast of Haiti. Wetlands Ecology
Management. 9: 271-278.

4Dinerstein, E. et al. 1995. A Conservation Assessment of the Terrestrial Ecoregions of
Latin America and the Caribbean. The World Wildlife Fund.

5Fourquren, J and Robblee, M Florida Bay: a history of recent ecological changes.
Department of Biological Sciences and Southeast Environmental Research.

6Hograth, P. 1999. The Biology of Mangroves. The Oxford University Press.

7Macintosh, D. and Zisman, S. 1999. The Status of Mangrove Ecosystems: rends in the Utilisation and
Management of Mangrove Resources.

8Mazda, Y., Magi, M., Nanao,H., Kogo, M., Miyagi, T., Kanazawa, N., and Kobashi, D. 2002.
Coastal erosion due to long-term human impact on mangrove forests. Wetlands Ecology
and Management. 10: 1-9.

9Miller, M., and Gerstner, C. 2001. Reefs of an uninhabited Caribbean island: fishes, benthic
habitat, and opportunities to discern reef fishery impact. Biological Conservation. 106: 37-44.

10Quarto, Alfredo. 2000. The Rise and Fall of the Blue Revolution. East Africa Wildlife SocietyÕs
Magazine SWARA. http://www.earthisland.org.

11Raven, P., Evert, R., and Eichhorn, S. 1986. The Biology of Plants. pp. 410, 506.

12Robertson, A.I., and Alongi, D.M. 1992. Tropical Mangrove Ecosystems. American
Geophysical Union.

13Ronnback, Patrik. 1999. The ecological basis for economic value of seafood production
supported by mangrove ecosystems. Ecological Economics. 29: 235-252

14Sneadaker, S., and Snedaker, J. 1984. The mangrove ecosystem: research methods.
United Nations Educational Scientific and Cultural Organizations.

15Tomlinson,P.B. 1986. The Botany of Mangroves. Cambridge University Press.

Website Sources:
16http://www.agiweb.org/gap/legis106/oceans.html AGI update on Federal Ocean and Coastal
Zone Policy.

17http://www.earthisland.org/map/index.htm The Mangrove Forest. Quarto, Alfred.
Mangrove Action Project

18http://www.serc.si.edu/biocomplexity/florida.htm Smithsonian Environmental Research Center. Biological Complexity of Mangrove Systems. Changing Characteristics of mangrove systems in southern Florida.

19http://www.nhmi.org/mangrove/index.html Newfound Harbor Marine Institute. 1997.

20http://everglades.fiu.edu/sfnrc/index.html South Florida Natural Resource Center. Mangrove Ecology. Armentano, Thomas. 1995.

21http://everglades.fiu.edu/sfnrc/index.html South Florida Natural Resource Center. Mangrove Mortality in Florida Bay. Carlson, P., and Brinton, S. 1995.

22http://www.epa.gov/epahome/hi-coastal.htm United State Environmental Protection Agency.
Environmental report card on coastal waters. 2002.

23http://www.afrol.com/Categories/Environment/backgr_mangroves.htm The mangroves, an
undervalued biotope.

24http://www.hrw.org/reports/1999/nigeria/Nigew991-01.htm#p190_8265 Human Rights Watch.
1999.

25http://www.foodfirst.org Farming Shrimp, Harvesting Hunger: The costs and benefits of the Blue
Revolution.

Pnuemataphores

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