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 than tropical corals because there are no zooxanthellae to feed them. "Lophelia" has a linear polyp extension of about per year. By contrast, branching shallow-water corals, such as "Acropora", may exceed 10–20 cm/yr. Reef structure growth estimates are about per year. Scientists have also found "Lophelia" colonies on oil installations in the North Sea. Using coral age-dating methods, scientists have estimated that some living deep-water corals date back at least 10,000 years. Deep-water corals use nematocysts on their tentacles to stun prey. Deep-water corals feed on zooplankton, crustaceans and even krill. Coral can reproduce sexually or asexually. In asexual reproduction