Mangroves are tropical trees and shrubs that grow in intertidal areas. They can also refer to the forest communities with their associated microorganisms (bacteria, fungi, algae) and fauna (molluscs, crabs, shrimps, and fish). Because they are exposed to extreme environmental factors of high salinity, alternating water saturation and desiccation, and anaerobic substrates, mangroves have developed coping mechanism such as salt glands on their leaves, varying root structures such as prop roots and pneumatophores, and viviparous (germinating) seeds.
Mangroves are highly productive ecosystems which are not only able to provide a range of valuable forest products, but also maintain estuarine water quality and play crucial roles in the life cycle of many commercially important species of fish and prawns.
Thirty-five percent of the total 18 million ha of mangrove forests are found in the Southeast Asian countries of Brunei Darussalam, Cambodia, Indonesia, Malaysia, Myanmar, the Philippines, Thailand and Vietnam. Indonesia alone has 4.5 million ha of mangroves.
But human activities, including aquaculture, have put these mangroves at risk. In the last three decades, mangrove loss has ranged from 25% in Malaysia to 50% in Thailand. In the Philippines, the mangrove cover of 418,990 ha in 1967 has been reduced to only about 100,000 ha now. This reduction was mainly caused by charcoal and firewood utilization, followed by the expansion of agricultural areas, fishponds, urban and industrial development, harbor construction, mining, and housing projects. With the rise in human population comes the demand for agriculture, aquaculture, and industrial development.
Products taken from the mangrove ecosystem range from construction materials to reptile skins and honey. Currently, mangroves in developing countries are being harvested and chipped for pulp and particle board on a very large scale by companies from developed countries. In addition, mangroves are used as an important and potentially sustainable source of fuelwood and charcoal to meet the increasing needs of developing countries for domestic fuel. Interest has also arisen in species like Nypa palm, which produces alcohol that can be turned into transport fuel.
Other natural products are harvested from mangroves. Crabs are very common on the mud flats in most mangrove ecosystems and are often a very important subsistence of even commercial food source. In some systems, edible shellfish are supported on the roots and trunks of mangroves.
These direct uses often sustain communities whose economy is based on harvesting the fish, shellfish, crustaceans, wood and other minor products which may be gathered. The continued viability of these ecosystems and the well- being of these people depend on managing the resource in a sustainable fashion. Locally important industries, providing rural employment, are also base on the mangrove resource.
On the other hand, mangroves reduce coastal erosion. They serve to dampen storm surges and to a minor extent high winds, both of which are associated with many tropical and subtropical storms. While the mangrove coastal barrier may be battered and damaged in severe storms, it will grow back naturally, without cost to man. No man-made coastal protection barrier is capable of self-repair.
The mangrove resource, where it occupies flood plains, performs a flood reduction function which may be lost if the area is filled and converted to other uses. Mangroves lining and banks of rivers also help prevent erosion of the riverbanks, which in turn helps protect adjacent property.
The mangrove area is spawning and nursery area for many marine species of fish. Moreover, the particles of vegetation (detritus) and nutrients exported out of the mangrove ecosystem from the food base of the complex of marine organisms which, in turn, support valuable estuarine and near-shore fisheries (finfish, shellfish and crustaceans). Those whose livelihood depends on fishing have long recognized the interconnection between the mangroves and fisheries, but these values have only slowly been considered in planning processes where decisions on allocations of intertidal land are being made.
The interesting and unusual fauna and flora of the mangrove community, particularly the bird life which feeds or shelters there, provides valuable opportunities for education, scientific study and tourism. While it is difficult to put monetary value on these wildlife-based activities, they are nonetheless significant uses which add to the importance of mangroves.
Mangrove resources are now under growing pressure as a result of population growth and economic development. Human activities and interventions within and near mangrove areas usually lead to the degradation of mangroves and the coastal ecosystem as well. The demand for wood and wood products is increasing and mangrove forests are being cleared for the construction of aquaculture ponds especially for shrimp and reclaimed for the cultivation of rice, coconuts or other crops.
Mangrove conservation and development can only be meaningful with an integrated coastal zone management (ICZM). Such ICZM programs need to be community-based in order to harmonize the varying interests and needs of various stakeholders in the coastal zones, e.g., fisheries, aquaculture, settlements and navigation.
The mangrove forest itself has designated zones for protection, production, recovery and development. The protected forest or preservation-conservation zone provides coastal protection, biodiversity, maintenance, ecotourism and scientific research. The productive or sustained yield zone is mainly for the harvest of forestry and fisheries goods for domestic or commercial use. The conversion zone (marginal and landward portions) can be developed into culture ponds, salt beds, agriculture, etc., and the recovery zone is for mangrove rehabilitation by replanting seedlings or wildlings or natural regeneration. A good rule of the thumb is to develop not more than 30% of a given mangrove area. An equally important guideline is the retention (or planting) of greenbelts or buffer zones between aquaculture ponds and adjoining waterways (shoreline, riverbank, etc.) or between adjacent uses (e.g. shrimp pond and rice field) of the coastal zone.
Not all aquaculture requires clearcutting of mangroves. Examples of mangrove-friendly aquaculture exist either in waterways (seaweeds; bivalves such as mussel, oyster and cockles; and cages for crab and fish) or land-based (ponds and pens for crabs, shrimps and fish). These technologies, particularly mangrove ponds and pens (also called aquasilviculture or silvofisheries) integrate the utilization of mangroves for both forestry and aquaculture production. (Excerpts from JH Primavera's paper in the Proceedings of the Mangrove-Friendly Aquaculture Seminar)
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ASIAN MANGROVES-TRADITIONAL USES AND PROSPECTS FOR RESPONSIBLE MANAGEMENT* By J.H. Primavera [Download PDF Format - File Size: 1.96 MB] *paper presented during the Mangrove Conference 2003, Salvador, Bahia, Brazil, 20-24 May 2003 |