Coral reefs are highly productive complex communities thriving in warm, well-lighted, marine environments. Their gross annual primary productivity is roughly 20 times greater fhan the open ocean, 10 times greater than coastal waters, and over three times greater than upwelling zones ( Odum, 1971).
The immense concentration of life on coral reefs is sustained primarily by a coral-algal symbiosis and the coral's ability to efficiently hoard and recycle nutrients received from flowing water.
The coral-algal colony contribute to the primary productivity and structural complexity of the reef community. The coral algae's primary productivity is transferred to higher trophic levels through direct release of algal photosynthetic products, and predation upon the coral and its by-products by other organisms. The various coral forms provide an elaborate shelter creating new niches and enlarging niche size. The diversity and number of reef niches determine the density of fish and invertebrate populations.
Reef organisms are best adapted to low stress environments. Consequently, most reef species are particularly vulnerable to changes in temperature, salinity, siltation, as well as pollution and other forms of human interference. Once the integrity of the reef has been disturbed, its recovery may take decades (Maragos et. al., 1973, Pearson 1974, Johannes 1976).