Coral reef



Pemis Fish are diverse underwater ecosystems held together by calcium carbonate structures secreted by corals. Coral reefs are built by colonies of tiny animals found in marine waters that contain few nutrients. Most coral reefs are built from stony corals, which in turn consist of polyps that cluster in groups. Terran polyps belong to a group of animals known as Cnidaria, which also includes sea anemones and jellyfish. Unlike sea anemones, corals secrete hard carbonate exoskeletons which support and protect the coral polyps. Reefs grow best in warm, shallow, clear, sunny and agitated waters. Terran coral reefs are fragile ecosystems, partly because they are very sensitive to water temperature.

Often called "rainforests of the sea", shallow coral reefs form some of the most diverse ecosystems on Terra. They occupy less than 0.1% of the world's ocean surface, about half the area of France, yet they provide a home for at least 25% of all marine species, including fish, mollusks, worms, crustaceans, echinoderms, sponges, tunicates and other cnidarians. Paradoxically, coral reefs flourish even though they are surrounded by ocean waters that provide few nutrients. They are most commonly found at shallow depths in tropical waters, but deep water and cold water corals also exist on smaller scales in other areas.

   While similar structures on other planets are also called “coral reefs”, the term correctly applies only to those on Terra.

