Coral island

A coral island is a type of island formed from coral detritus and associated organic material. It occurs in tropical and sub-tropical areas, typically as part of a coral reef which has grown to cover a far larger area under the sea. The term low island can be used to distinguish such islands from high islands, which are formed through volcanic action. Low islands are formed as a result of sedimentation upon a coral reef or of the uplifting of such islands. Coral reefs are some of the oldest ecosystems on the planet, over geological time forming massive reefs of limestone. The reef environment supports more plant and animal species than any other habitat. Coral reefs are vital for life for multiple aspects some of which include structure, ecology, and nutrient cycles which all support biodiversity in the reefs. Coral reefs build massive calcareous skeletons that serve as homes for animals such as fish hiding inside the crooks and crannies of the reef and barnacles attaching themselves directly to the coral's structure. The structures also help plants that need the sun to photosynthesize, by lifting the plants to the ocean's surface where the sunlight can penetrate the water. The structures also create calm zones in the ocean providing a place for fish and plant species to thrive. Over geological time a reef may reach the surface and can become a coral island, where it begins a whole new ecosystem for land-based creatures. A coral island begins as a volcanic island over a hot spot. As the volcano emerges from the sea, a fringing reef grows on the outskirt of the volcano. The volcano eventually moves off the hot spot by means of plate tectonics. Once this occurs, the volcano can no longer keep up with the wave erosion and undergoes subsidence. Once the island is submerged, the coral must keep growing to stay in the epipelagic zone. This causes the coral to grow into an atoll with a shallow lagoon in the middle. The lagoon can then undergo accretion and create an island completely made of carbonate materials.