H, 2000).According to Morgan and Chenn (1999), coral reefs are very fragile, because reef-building organisms cannot thrive if the surrounding water changes significantly. Coral reef-building corals are found only in clear areas within 50m of the water surface and where the temperature of the water remains above 200 throughout the year.
A single reef contains an abundance of different species of coral. In turn, these corals support a tremendous variety of other life this reef will act as a source of food for a large number of sea creatures as well as a home. As an example, the Great Barrier Reef in Australia is a home for more than 2000 species of fish (Encarta, 2002). Coral reef also provides shelter for reef animals such as sponges, sea anemones, Bryozoans, sea cucumbers, sea urchins,shrimps,carbs, lobsters, octopuses, squids, nudibranch, sharks, wrasses, eels, angelfish, seahorses and sea turtles (Corals and Coral Reefs, 2002). It is rank among the most biologically productive of all ecosystems as it harbor 950 000 species which is about 9% of the world's total (Reiss, Chapman, 2000) Besides, it contains 22 of 23 animal phyla found on the planet (More on Coral Reefs, 2002). Without reefs, marine species will lose its habitat and gradually facing extinction. Hence, the coral reefs need to generate new cells for reef-building. This can be done by the symbiotic relationship between the coral animals and the unicellular algae called zooxanthellae (Lin, S.H., 2002). The zooxanthellae export organic compounds to their host by photosynthesis as well as nourishing the growth of coral skeleton by the deposition of calcium carbonate (Chenn and Morgan, 1999). Meanwhile, the zooxanthellae will gain high concentration of nutrients by living inside the polyp cells of coral reefs as the nutrient concentration are stable within the cytoplasm of the host compare to the external environment where nutrient level is fluctuating widely (Reiss and Chapman, 2000).