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
Coral reef of Varadero Coral reef of Varadero Coral reef of Varadero is a coral reef located in the Bay of Cartagena, Colombia. Its paradoxical existence, harboring high coral cover and diversity despite the poor water quality and sediments discharged during the last 500 years by the Canal del Dique into the Bay, has drawn special interest by the scientific community and local and international media. The persistence of the Varadero reef is currently threatened by a project to modernize Cartagena’s port, not only by the direct damage produced by the dredging of a new shipping lane through the reef, but also by the