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Mangroves

What are mangroves?

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.

Functions and Values/Benefits

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.

Bangkerohan (Protected area)

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.

Tarahid (Protected area)

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.

Cabuyoan (Protected area)

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.

Source: SEAFDEC

Mangrove Crabs

Mangrove crabs are crabs that live among mangroves, and may belong to many different species and even families. They have been shown to be ecologically significant in many ways. They keep much of the energy within the forest by burying and consuming leaf litter. Furthermore, their feces may form the basis of a coprophagous food chain contributing to mangrove secondary production (Lee, 1997; Gillikin et al., 2001). As mentioned in Robertson et al. (1992), crab larvae are the major source of food for juvenile fish inhabiting the adjacent waterways, indicating that crabs also help nearshore fisheries. The crabs themselves are food for threatened species such as the Crab Plover (Seys et al., 1995; Zimmerman et al., 1996). Their burrows alter the topography and sediment grain size of the mangrove (Warren and Underwood, 1986) and help aerate the sediment (Ridd, 1996).

Click the shaded area on the map to open the info window. Red color as the highest production volume and white color for zero production.

"Smith et al. (1991) found that removing crabs from an area caused significant increases in sulfides and ammonium concentrations, which in turn affects the productivity and reproductive output of the vegetation. Their findings support the hypothesis that mangrove crabs are a keystone species."

Source: Wikipedia

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