In natural terms mangroves are halophytic species of trees that are adapted to wet soils and saline habitats and are subject to periodic tidal submergence. Some factors that control the mangrove distribution are climate, salt water, tidal fluctuation & substrate (7). Mangroves develop where the annual temperature is below 19o C (2). Extensive mangroves occur where the average temperature of the coldest month is higher than 20oC and the seasonal range doesn’t exceed 5o C, except in East Africa where the range can be 10o C (2). They don’t tolerate temperature fluctuations exceeding 10o C or temperatures below freezing (2). Mangroves are facultative halophytes (4). The salt is not a physical requirement for their development because they are capable of growing in fresh water areas (4). The tides help in the dispersal of mangrove propagules and detritus, transport nutrients, export some organic carbon & help balance the soil salinities in areas of high evaporation rates (6). Mangroves grow at their peak level in depositional environments with low wave energy (2). High wave energy can prevent the establishment of propagules, destroy the root system and prevent the accumulation of fine sediments (6).
In the economical approach mangroves are viewed differently because they are viewed as an insatiable and unlimited product. The economical approach of mangroves is seen as goods and services provided by nature when, at any given time, they can become limited or scarce. In this approach we should be careful because our needs for a particular material can be satisfied over a short period of time. Are we able to exploit and get enough from nature? Can the natural resource be unlimited?
The estimated dollar value of mangroves and tidal marshes expressed, as total value per hectare/year is $ 9,990 and the total global value per year is $1.6 trillion (14). The estimated mangrove acreage is not well known but it is believed that today’s mangrove forests comprise 15.8 million hectares (0.6% of all inland forests of the world)(14). The world’s tropical coastline is dominated by mangroves and extends over 15.5 million ha worldwide (1). This is roughly half the original mangrove acreage covered, and they are fast declining at a rate of 2-8% per year (14). In Bangladesh there is 600,000 ha of mangroves, 6.9 million ha in the Indo-Pacific region, 3.5 million in Africa, 4.1 million ha in the Americas including the Caribbean (1).
In Puerto Rico the original mangrove acreage was estimated at 30,000 hectares (5). By 1975 only half the area remained (5). In Florida, the southeast coast in Tampa Bay lost over 44% of the coastal wetlands acreage (this included mangroves & salt marshes)(10). In other parts of the world like in Thailand mangroves are been lost progressively since 1961 it had lost 203,000 ha with over a 50% reduction in total mangroves (14). In the Philippines the total mangrove area decreased was from a total of 448,000 ha to 110,000 by 1990 (14). Other countries of the world like Indonesia keep loosing mangrove acreage and Java alone lost 70% of its mangroves (14). The mangrove loss is evident worldwide and the mangrove value will increase as they become less abundant on all the world coastlines.
Mangroves are important in natural and economical aspects.
Natural importance of mangroves (4), (6), (7), (10) & (13) are:
* They stabilize shorelines, providing them with protection from storm surges and ocean currents. Mangroves serve as a buffer zone between land and sea.
* Mangroves help prevent soil erosion & reclaim land from seas.
* They serve as a breeding area and nursery grounds for a number of marine organisms. An estimated 75% of fish caught commercially spend some time in the mangrove or are dependent on food chains, which derive from these coastal forests.
* Shelter for many wildlife species and associated organisms to mangrove roots. Many species use the environment dominated by mangrove trees for food and shelter during part or all of their life cycles. The surface soil of mangrove swamp is alternatively inundated and drained. It supports animals such as crabs, amphibians, reptiles, air-breathing fishes, and mammals, whose distributions are governed by degree of tidal penetration and by nature of the substratum.
* Sediments trapped by the mangrove roots prevent silting of adjacent marine habitat.
* Highly productive habitat.
* Nutrient cycling & carbon export. There is constant movement of living matter into and out of the mangrove swamp.
* Biomass production converted into litter fall that later decomposes.
* They serve as a reservoir in the tertiary assimilation of waste.
* Recreation.
Economical Uses of Mangroves (1) & (3):
* Mangroves serve as a source of tannins for the leather industry.
* Commercial use for the production of timber for building, firewood & charcoal.
* Honey collection from mangrove areas in West Bengal and Orison.
* Medicinal Uses: tea derived from the bark could alleviate diabetes, kidney stones, skin diseases and improve kidney function and purify blood.
* Salt Production.
* Food Source (Fisheries).
* Tourism.
* Pasture.
* Fuel.
* Construction material/Source of wood for the construction of tobacco galleries, walls/fences, poles, stakes, posts, beams & tapos or fish traps and ceiling supports).
* Others (Table #1& #2).
Causes & Examples of Mangrove Degradation
The diverse human activities that people realize in mangrove areas can lead to mangrove loss & degradation. Mangroves are a type of wetland and are threatened worldwide. The habitat loss is the primary reason for endangerment (15). The ecological change is a major cause because of the loss of mangrove areas, overexploitation, pollution, changes in water quality & introduction of new species (9). In most parts of the world the mangrove areas are converted to other uses for human benefit. This means that the land use has been altered. In Ecuador, it was estimated that 25-40% of the mangroves have been lost due to extensive shrimp aquaculture (14). Because of the mangroves high productivity, they are target areas for shrimp pond development. When a mangrove area is cut down for shrimp aquaculture, the intricate and productive system is destroyed (15). In Thailand 65,000 ha were lost due to shrimp farming alone (14). Some countries that convert mangroves into shrimp industries are the Philippines, Thailand, Ecuador, Indonesia & others (1).
Vast areas of mangrove forest have been already lost in Southeast Asia and most parts of South Africa due to wood extraction, conversion to agriculture, coastal industrialization and urbanization. The pressures of increased population, food production and industrial and urban development have been appointed as potential cause of mangrove degradation and devastation (1). In the United States of America (USA), mangroves are being adversely affected by both nearby developments and pollution problems. Today there is a 50-acre (20.23 ha) of dead mangroves from a Westinghouse Co. “ Pelican Bay Development Project “ just north of Everglades National Park in Naples, FL.
To finalize, I should mention Puerto Rico’s mangroves degradation. The mangroves are been degraded in Martin Pe–a due to the presence of houseboats anchored on the mangrove fringe. Today, the construction of housing and hotel complexes are threatening a vast area of healthy mangroves in the jurisdiction of Luquillo and Fajardo. The development plans to build over 3,000 rooms for lodging, 3 golf courses, a marina and parking lots in a pristine area.
Consequences of Mangrove Forest Loss
The most evident cause of mangrove forest lost is the coastal erosion because of the global warming and the loss of mangrove that serve as a buffer zone between land and sea. This occurs because the mangrove area is been reduced and the capability of trapping sediments becomes lesser. Another cause is the sedimentation of sensitive coastal habitats such as coral reef and to a lesser extent, sea grasses. The mangroves retain the sediments from reaching other ecosystems with a higher vulnerability. Sedimentation downstream and along coral reefs occur when mangrove no longer hold soil in place (14). In 1991, thousands of people were killed by a tidal wave in Bangladesh where shrimp farms had replaced mangroves (14).
Future Predictions for Mangrove Communities - Mangrove Acreage vs. Economic Value
Coastal areas worldwide where mangroves occur will be more threaten by ocean currents and storm surges. The turbidity rates on the continental shelf will raise and this will endanger corals. The coastal areas will continue to suffer from eutrophication. If there is no legislation on maintaining mangroves acreage worldwide we will see in the future more mangrove loss due to conversion than any other kind of use for human benefit. The conversion to other kind of use in a mangrove forest is lethal, irreversible and sometimes involves high costs. The costs of keeping the resource the way it is, far outweighs the benefits of nature. Think about that when changing nature because the consequence can be complicated and there can be millions of dollars involved. We (society) end up paying for bad choices in resource management and use. The mangrove forest value will increase as they become less abundant and it’s the increase in value that can make them disappear one day. Why?
References:
A. Books & Primary Literature
1. Bandaranyake, W.M. “ Traditional & medicinal uses of mangroves “. Mangroves & Salt Marshes, 1998, vol. 2, p.p.133-148.
2. Chapman,V.J. Mangrove Biogeography. University of Puerto Rico, Department of Marine Science Library. Mayaguez, P.R. p.p. 22.
3. Kovacs, J.M. “ Assessing mangrove use at a local scale “. Landscape & Urban Planning, 1999, vol. 43, p.p. 201-208.
4. Nybakken, J.W. 1993. Marine Biology: An Ecological Approach. 3rd edition. Harper Collins College Publishers. p.p. 462.
5. Lugo, A. 1988. “ The Mangroves of Puerto Rico are in trouble “. Acta Cient’fica 2 (2-3): 124.
6. Odum, W.E., C.C. Mc Ivor & T.J. Smith III. 1982. The Ecology of the Mangroves of South Florida: A Community Profile. Bureau of Land Management, Fish & Wildlife Service, U.S. Department of Interior. FWS/OBS-81/24(January 1982). p.p. 144.
7. Walsh, G.E. 1974. In “ Ecology of Halophytes: Mangroves: A Review ”. Academic Press, Inc. New York & London. p.p. 605.
B.Website Sources
8. Barbier, E.B., M.A. Acreman & D. Knowler. 1997. “Economic Valuation of Wetlands: a guide for policy makers and planners”. Ramsar Website: http://www.ramsar.org p.p. 127.
9. http://www.ramsar.org/about_wetland_loss.httm “ A Global Overview of Wetland Loss and Degradation “ p.p. 14.
10. http://www.floridaplants.com/horticulture/mangrove.htm: “ Florida’s Mangroves: Walking Trees “.
11. http://www.godrejnet.com/mangroves/man7.htm: “ Importance of Mangroves”
12. http://www.nhmi.org/mangroves/rep.htm: “ Reproductive Strategies of Mangroves
13. http://www.env.qld.gov.au/environment/coast/habitats/m.html :” Mangroves - more than mud & moozies !
14. http://www.sierraclub.ca/national/shrimp/biod.html : “ Biodiversity & Mangroves “
15. http://www.earthisland.org/map/mngec.htm : “ Mangrove Action Project “
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