- Coral reefs 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.
- The 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.
- Often called “rainforests of the sea”, coral reefs form some of the most diverse ecosystems on Earth.
- They occupy less than 0.1% of the world’s ocean surface, about half the area of France, yet they provide a home for 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.
- Coral reefs deliver ecosystem services to tourism, fisheries and shoreline protection.
- The annual global economic value of coral reefs is estimated between US$29.8-375 billion.
- However, coral reefs are fragile ecosystems, partly because they are very sensitive to water temperature.
- They are under threat from climate change, oceanic acidification, blast fishing, cyanide fishing for aquarium fish, sunscreen use, overuse of reef resources, and harmful land-use practices, including urban and agricultural runoff and water pollution, which can harm reefs by encouraging excess algal growth.