Coral Reef Structure and Ecology

Coral Reef Definition and Biology

A coral reef is an underwater ecosystem built primarily by colonies of reef-building corals. Coral polyps are animals in the class Anthozoa within the phylum Cnidaria, related to sea anemones and jellyfish. Unlike sea anemones, corals secrete hard calcium carbonate exoskeletons that support and protect them; over generations, these skeletons accumulate to form reef structures. Many reef-building corals live in mutualistic association with microscopic algae called zooxanthellae, which provide energy through photosynthesis and help corals grow in nutrient-poor waters. Coral reefs generally develop best in warm, shallow, clear, sunlit, and well-agitated tropical waters, although deep-water and cold-water reefs also exist. Their structure creates complex habitats that support exceptionally high biodiversity, including fish, mollusks, crustaceans, worms, echinoderms, sponges, tunicates, and other cnidarians. Reefs occupy less than 0.1% of the ocean but provide habitat for at least 25% of marine species. They are also important for fisheries, tourism, and shoreline protection, but are threatened by warming waters, ocean acidification, pollution, nutrient runoff, overfishing, destructive fishing practices, and other human activities.

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Coral Reef Growth Conditions

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