A reef is built from the refuse and remains produced and held in place by various reef residents on a rigid framework of coral. By studying reefs, we learn about the biodiversity of underwater life, the interdependence of animals within an ecosystem, and the factors affecting reef formation.
Coral reefs thrive in sites with clear, shallow water and stable, warm temperatures.
Polyps provide a reef's foundation with the calcium-rich skeletons produced by the outer layer of their skins. It takes billions of polyps centuries to build a reef that can provide shelter for an array of other animals. Around reefs live fishes and other animals, including sea fans, a kind of octocoral, as well as starfish and sea urchins, both members of the phylum Echinodermata.