| A reef is a living, coral community with several thousand organisms. There are over 500,000 species in the 600,000 square miles of coral reefs. Millions of species of fish, eels, sponges, grasses, algae, mollusks, crabs, worms, and other marine animals use reefs as homes or as nurseries for their young. Tons of coral make up the coral reefs. After the coral dies, it leaves its skeletons, made of calcium carbonate, behind. There are three different kinds of reefs: fringing reefs, barrier reefs, and atolls. The reefs that are near shore and are separated from land by low water are called fringing reefs. Reefs that are at least 10 kilometers away from land are called barrier reefs. A circular coral island that is far away from land is called an atoll. Atolls form when coral develops on a volcanic island that has sunk below the water. For any of these reefs to form takes hundreds of years. It may take up to 100 years for an inch of coral reef to grow! |