Most reef-building corals contain photosynthetic algae, called zooxanthellae, that live in their tissues. The corals and algae have a mutualistic relationship. The coral provides the algae with a protected environment and compounds they need for photosynthesis. In return, the algae produce oxygen and help the coral to remove wastes. Most importantly, zooxanthellae supply the coral with glucose, glycerol, and amino acids, which are the products of photosynthesis. The coral uses these products to make proteins, fats, and carbohydrates, and produce calcium carbonate (Barnes, R.D., 1987; Barnes, R.S.K. and Hughes, 1999; Lalli and Parsons, 1995; Levinton, 1995; Sumich, 1996). The relationship between the algae and coral polyp facilitates a tight recycling of nutrients in nutrient-poor tropical waters. In fact, as much as 90 percent of the organic material photosynthetically produced by the zooxanthellae is transferred to the host coral tissue (Sumich, 1996). This is the driving force behind the growth and productivity of coral reefs (Barnes, 1987; Levinton, 1995).
plants. Because their algal cells need light for photosynthesis, reef corals require clear water. For this reason they are generally found only in waters with small amounts of suspended material, i.e., in water of low turbidity and low productivity. This leads to an interesting paradox—coral reefs require clear, nutrient-poor water, but they are among the most productive and diverse marine environments (Barnes, 1987).
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