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Coral Reef EcosystemsCoral reefs are the most biologically diverse marine ecosystems on earth, rivaled only by the tropical rainforest on land. Coral reefs are very important to people. The value of coral reefs have been estimated at thirty billion U. S. dollars and perhaps as much as one-hundred and seventy-two billion U.S. dollars each year, it provides food, protection of shorelines, jobs based on tourism and also it provide medicine. Coral reefs occupy less than one quarter of one percent of the earth’s marine environment and they are home to more than one-fourth of all known fish species. As unique and valuable as these ecosystems are, they have become one of the most threatened coastal ecosystems. A recent World Resources Institute report estimates that nearly sixty percent of the world's reefs are threatened by increasing human activity. As human population continues to increase so will the threats to reefs.A coral reef is made up of thin plates of calcium carbonate that has been secreted over thousands of years by billions of tiny soft bodies’ animals called polyps. It takes years for some corals to grow an inch. Each polyp excretes a calcareous exoskeleton and lives in a symbiotic relationship with a host, zooxanthella that gives the coral its color. The zooxanthellae take in the carbon dioxide and processes it through photosynthesis and then releases the oxygen as a by-product which is then used by the host, polyp. Millions of polyps grow on top of the lime stones that are the remaining of the former colonies and they form new reefs. Most coral reefs are surrounded by nutrient-poor ocean waters so their high productivity is surprising. This can be contributed a