A coral reef is an underwater ecosystem characterized by reef-building corals. The reefs are formed by colonies of coral polyps that are held together by calcium carbonate. Most coral reefs are constructed from stony corals, whose polyps are grouped into groups.
The coral belongs to the Anthozoa class on the Cnidaria animal phylum, which includes sea anemones and jellyfish. Unlike sea anemones, the corals secrete the hard carbonate exoskeletons that support and protect the coral. Most reefs grow better in warm, shallow, clear, sunny, and bustling waters.
Often called the “rainforests of the sea”, shallow coral reefs form some of the most diverse ecosystems on Earth. They occupy less than 0.1% of the world’s oceanic zone, about half of the area of France, nevertheless provide a home for at least 25% of every marine species, including fish, mollusks, worms, crustaceans, echinoderms, sponges, tunics and others Cnidarians. Coral reefs flourish in oceanic waters that provide few nutrients. They are more commonly found in the superficial depths in tropical waters, nevertheless deep waters and cold-water coral reefs exist on smaller scales in other areas.