Coral reef A fringing reef forms around an extinct volcanic island as the island and ocean floor subsides. As the subsidence continues, the fringing reef becomes a barrier reef and ultimately an atoll reef. Darwin predicted that underneath each lagoon would be a bedrock base, the remains of the original volcano. Subsequent research supported this hypothesis. Darwin's theory followed from his understanding that coral polyps thrive in the tropics where the water is agitated, but can only live within a limited depth range, starting just below low tide. Where the level of the underlying earth allows, the corals grow around the coast
Deep-water coral off Africa’s west coast. In addition to ocean bottoms, scientists find "Lophelia" colonies on North Sea oil installations, although oil and gas production may introduce noxious substances into the local environment. The world's largest known deep-water "Lophelia" coral complex is the Røst Reef. It lies between deep, west of Røst island in the Lofoten archipelago, in Norway, inside the Arctic Circle. Discovered during a routine survey in May 2002, the reef is still largely intact. It is approximately long by wide. Some further south is the Sula Reef, located on the Sula Ridge, west of Trondheim on the mid-Norwegian Shelf,