11.2.4.3. Coral Reefs

Coral reefs play a crucial role in fishery production and in protecting the coastline from wave action and erosion (Ruddle et al., 1988; Middleton, 1999). Southeast Asia has almost one-third of the world's mapped coral reefs (Pennisi, 1997); these reefs extend to the northern extreme range in Japan (Nishioka and Harasawa, 1998). Coral reef productivity is a function of their structure, biological recycling, and high retention of nutrients. Reefs in Indonesia and the Philippines are noted for extraordinarily high levels of biodiversity: Each contains at least 2,500 species of fish. Severe coral bleaching can occur as a result of seawater warming and clear skies (resulting in higher incident solar radiation).

Major coral bleaching events have occurred in 1983 (Japan, Indonesia), 1987 (Maldives), 1991 (Thailand, Japan), 1995 (Thailand, Philippines), and 1998 (Maldives, Sri Lanka, India, Indonesia, Thailand, Japan, Malaysia, Philippines, Singapore, Vietnam, Cambodia). As a result of the major 1998 coral bleaching in the south Asia region, many reefs dominated by branching species have been severely damaged, with high mortality of these species. In coastal seas around the Maldives, Sri Lanka, the Andaman Islands of India, and Japan, reef community structure has switched from dominance by fast-growing branching species to monopolization by the more physically rigorous and slow-growing massive corals (Wilkinson, 1998). Deforestation in many island countries of Asia and quarrying of live corals for manufacture of calcium carbonate have led to significant coral decline or severe damage to the entire ecosystem.

Studies show that a moderate rise in sea level around the coast of Thailand would stimulate the growth of coral reef flats and extend corals shoreward. The enhanced growth potential is likely to be restricted by human infrastructure and development along the coast (Chansang, 1993). Asia's coral reefs are undergoing rapid destruction in terms of habitat richness (Cesar et al., 1997; Nie et al., 1997; Pennisi, 1998) as a result of several factors, including extreme temperatures and solar irradiance, subaerial exposure, sedimentation, freshwater dilution, contaminants, and diseases (Glynn, 1996). Virtually all of the Philippines' reefs and approximately 83% of Indonesia's reefs are at risk from destructive fishing techniques, reef mining, sedimentation, and marine pollution (Middleton, 1999; UNEP, 1999). The increase in atmospheric CO₂ concentration (resulting in higher CaCO₃ concentrations in seawater) and consequent rise in sea surface temperature (SST) is likely to have serious damaging effects on reef accretion and biodiversity.

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