Coral reefs are arguably the world's most beautiful habitats. Coral reefs have been called the rainforests of the oceans, because of the rich diversity of life they support. In Australia, the Great Barrier Reef is the largest deposit coral in the world with the reef extends about 2,010 km from Mackay, Queens land, to the Torres Strait. On worldwide basis, coral reefs cover an estimated area of approximately 600 000km2, lying with the tropical belt delineated by the 30 0 latitude to the north and south. (Encarta, 2002) The richest regions of the world's coral reefs are the South-East Asian seas and Indian Ocean; both combined account for over half of the world's coral reefs with the coral reefs in South-East Asia constitute 30% of the world's coral reefs (Lin,S.H, 2000). Coral reefs are generally classified into three types: barrier reefs, fringing reefs, and atolls. Both barrier reefs and atolls are both characterized by a lagoon that is protected on the seaward side by the reef. Barrier reefs occur in association with continental land masses, whereas atolls are coral reefs that form atop submarine volcanoes.(More On Coral Reefs, 2002) Fringing reefs are coral reefs that grow in shallow waters and border the coast closely or are separated from it by a narrow stretch of water and it is considered immature.
The formation of the coral reef is not just a matter of deposition of calcium carbonate by the coral polyps. There are two phases in the formation of coral reefs - the "constructive" phase and the "destructive" phase ( Lin,S.H, 2000). The constructive phase involving the deposition of new calcium carbonate over old substratum while the destructive phase involves the breakdown of the reef structure due to the boring actions of numerous bivalves, sponges and worms ( Lin,S.H, 2000). The coral growth is confined mainly to the upper 20 meters of water with rapid growth being on the upper reef slope below the crest ( Lin,S.