Coral Reefs Are Built From the Skeletons of Tiny Animals
Coral reefs are built by tiny coral animals called polyps, which make hard calcium-carbonate skeletons that accumulate into huge reef structures.
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A coral reef may look like a giant underwater rock formation, but its foundation is built by countless tiny animals. Reef-building corals are made of individual animals called polyps. Each polyp is a small soft-bodied creature that secretes a hard skeleton made mainly of calcium carbonate. As colonies grow, new skeleton is added on top of older material, while generations of coral build and expand the structure over long periods. Large colonies can contain enormous numbers of individual polyps, and reefs can become massive structures over time. Many reef-building corals also live with microscopic algae inside their tissues. The algae use sunlight to make food, while the coral provides the algae with a protected place to live. This partnership helps support coral growth and the wider reef ecosystem. The hard skeletons provide the physical framework that shelters many other marine organisms, helping reefs become highly diverse habitats. Not all corals build reefs, however. Soft corals, for example, do not produce the same rigid calcium-carbonate structures that create massive reef foundations.
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