6. Habitat degradation
Mangrove forest is a productive ecosystem and constitutes a natural barrier against storm surges and strong winds. It serves as nursery and feeding grounds for many commercially important aquatic species. During the past 32 years (1961–1993), social and economic development have caused severe destruction of mangrove forests in Thailand. The existing mangrove forest area in Thailand has decreased more than 50% in the past 32 years (Kongsangchai, 1995). Changes of the areas are shown in Table 9. The deterioration of mangroves in the past and at present is approximately 6.2 thousand ha/year. The major causes are economic, political, and social pressures which can be separated into many activities as show in Table 10. It is clearly seen that the conversion of mangrove forests to shrimp farming is one of the most severe problems and has tremendous impacts on the coastal ecosystem. For example the removal of tree-cover, loss of nutrient-supply from the forest to the sea, obstruction of tidal flushing and fresh water runoff, coastal erosion and the discharge of waste from ponds lead to change in the natural equilibrium and ultimately to the ecosystem destruction. Human activities can directly cause catastrophic mortality on reefs through dredging, dynamite fishing, and/or pollution. ONEB (1992) reported on the status of the coral reefs in the Thai waters during the period of 1987–1992 that only 36% remained in good condition, 33% in fair condition, 30% in poor condition (Table 11). It is expected that the destruction of the coral reefs will be more severe if preventive measures are not promptly taken.