Coral reefs are rock-like structures made from calcium carbonate secreted by corals. They are also called ‘rainforests of the sea’ as they provide shelter to a large number of marine organisms. Besides corals, sea anemones, starfish, octopus, sea urchins, and a variety of fish are found in coral reefs. Examples of coral reefs are the Great Barrier Reef of Australia and those of the Andaman and Nicobar islands in India.