Coral reefs are the marine equivalent of rainforests. They are home to huge numbers of a great variety of animals. Unlike some other habitats, few plants grow on coral reefs because fish and sea snails graze them. Ocean currents carry most of the food to the reef. Plankton is the basic food that powers the whole reef system. The small animals that feed on plankton are eaten by large crustaceans and fish, and so on up the food chain to predators such as sharks.
If a coral reef continues to grow it may begin to rise out of the water, becoming a coral island. The sea helps to break up the coral growths and pile them up. Creatures such as calcifying algae cement the pieces together to form a solid structure. If soil lodges in the coral vegetation often begins to grow on the surface. Many of the Pacific islands were formed in this way.
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