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Coral reefs are among the most diverse and productive communities on Earth. They are found in the warm, clear, shallow waters of tropical oceans worldwide. Reefs have functions ranging from providing food and shelter to fish and invertebrates to protecting the shore from erosion. Through symbiosis with unicellular algae (zooxanthellae), reef-building corals are the source of primary production in reef communities (Richmond 1993). Biologically active compounds produced by reef dwelling organisms possess antimicrobial and antiviral activity (Van Alstyne and Paul 1988). These compounds may be important sources for natural product based drugs and medicines. In addition, revenue from tourists attracted to the beauty of coral reefs can be a significant source of income for human communities in these areas. Unfortunately, as our understanding of corals and coral reefs increases, it becomes apparent that the effects of the human population on these communities may be increasing as well.
Reef-building (or hermatypic) corals are of the order Scleractinia in the class Anthozoa of the phylum Cnidaria. Approximately 6,000 species of Anthozoans exist, all of them marine (Pechenik 1991). Coral reefs of the western Pacific are much more diverse than those of the Atlantic and Caribbean. There are up to 75% more genera and 85% more species of corals in Pacific waters (Wilkinson 1987). Reefs are formed by calcium carbonate produced by tiny coral polyps. While corals are the chief architects of reef structure, they are not the only builders. Coralline algae cement various corals together with compounds of calcium, and other organisms such as tube worms and molluscs donate their hard skeletons (Cousteau 1985). Together these organisms construct many different types of reefs. Reefs are important land builders in tropical areas, forming islands and altering continental shorelines (Goreau et al. 1979).
A coral colony may consist of thousands of polyps. Polyps are typically carnivorous, feeding on small particles floating in the water. However, endosymbiotic algae known as zooxanthellae provide important sources of nutrition to hermatypic corals (Rowan and Powers 1991). Corals reproduce both sexually and asexually. An entire colony many meters in diameter can start out as a single polyp.
Because many coral reef organisms can tolerate only a narrow range of environmental conditions, reefs are sensitive to damage from environmental changes (Richmond 1993). Corals are susceptible to diseases and bleaching. Also, dramatic natural events such as hurricanes can damage coral reefs. In addition, many problems to reefs are anthropogenic (human caused). Because of the important ecological and economic roles coral reef communities fulfill, an understanding of the stresses and dangers to the reefs is necessary. Fortunately, many of the human induced hazards to coral reefs can be remedied (Richmond 1993).