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Why are reef-building corals usually colonial animals?

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coral reef The Great Barrier Reef, off the coast of Queensland, Australia, is the world's largest coral reef.

Reef-building corals are typically colonial because this structure allows them to build the massive, rigid frameworks necessary to construct a coral reef.

Unlike solitary corals, which remain individual organisms, reef-building stony corals begin as an initial polyp that divides into daughter polyps. These polyps continue to divide and grow side by side, often becoming so tightly packed that they share common walls. By precipitating calcium carbonate over centuries, these colonies create a continuous, heavy skeleton that is resistant to the physical forces of the ocean, such as storms and strong surf.12

This colonial growth is a cooperative effort; some of the largest reef structures represent the work of up to 1,000,000 tiny individuals. By living in colonies, these organisms can grow profusely, even over one another, to form the structural foundation of the reef ecosystem.21