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Coral Reefs

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Coral reefs grow in warm, sunny, regions, mainly between the Tropics of Cancer and Capricorn, extending further north and south only where there are warm currents in water that stays fairly warm year round. They cover over 600,000 miles, are home to over 5,000 species and are found in the waters of over 100 countries. Corals are tiny animals, called polyps somewhat like sea anemones, that secrete a stony cup of limestone around itself as a skeleton, forming a column end attached to the reef and a top end that moves about.  The polyps divide as they grow and form coral colonies, gradually forming a coral reef.  Some coral reefs may be many thousands of years old, formed slowly over time, reacting to changes in sea level and other environmental conditions.  There are many kinds of reefs.  Fringing reefs lie around islands and continents, separating the shore from the open seas by narrow shallow lagoons which usually have a sandy bottom.  Barrier reefs grow on the edge of continental shelves, separated from the shore by deep and wide lagoons. The 2 largest barrier reefs in the world are the Great Barrier Reef in Australia, which is about 2500 miles long, and the Belize Barrier Reef in the Caribbean.  Atolls form when islands surrounded by fringing reefs sink into the sea or when sea level rises around them. The fringing reefs keep growing and eventually form circles with lagoons inside. Atolls are found in the Pacific Ocean, the Indian Ocean and a few in the Caribbean.  Coral reefs protect our shorelines from erosive waves, are nurseries for growing fish, supply a source of protein for our diets, give food, shelter and protection almost one million marine species, provide jobs through fishing and tourism, serve as a growing source of medicine  and give us a wondrous underwater world to study and enjoy.