What structure do corals build that supports one-quarter of marine species?

Corals build coral reefs, ecosystems that support about one-quarter of marine species.

Reef-building corals are colonial animals called polyps. Each polyp secretes a skeleton of calcium carbonate, and generations of colonies can accumulate these skeletons into reefs. The result is a three-dimensional habitat full of crevices, surfaces and sheltered nursery areas.

Coral reefs occupy less than one percent of the ocean floor, yet they are among the most biologically diverse marine ecosystems. They provide food, coastal protection and economic resources for millions of people. Reef organisms include fish, molluscs, crustaceans, sponges and many microscopic life forms.

Most shallow tropical corals depend on symbiotic algae for much of their energy. Heat stress can disrupt this partnership and cause coral bleaching. Bleaching does not always mean immediate death, but prolonged stress can kill colonies and weaken the reef structure.