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
Réunion's coral reef for coral at Réunion is between 23 °C and 28 °C. Increased surface water temperature related to global warming can contribute to disease and bleaching of coral reefs, as is apparent on Réunion. Natural cyclones and anthropogenic disturbances such as urban development of catchment areas affect the reefs of Réunion. These ecological disturbances have led to an increase in coral reef nutrient levels via submarine groundwater discharge. Increased nutrient levels have resulted in the modification of flora and fauna in the benthic zone. The coral reef is a natural barrier that protects the coast from typhoons. The least vulnerable sectors