Atoll Atoll An atoll (, , , , or ), sometimes called a coral atoll, is a ring-shaped coral reef including a coral rim that encircles a lagoon partially or completely. There may be coral islands or cays on the rim. The coral of the atoll often sits atop the rim of an extinct seamount or volcano which has eroded or subsided partially beneath the water. The lagoon forms over the volcanic crater or caldera while the higher rim remains above water(s) or at shallow depths that permit the coral to grow and form the reefs. For the atoll to persist,
Marine wildlife of Baa Atoll Marine wildlife of Baa Atoll The marine wildlife of Baa Atoll consists of marine species living in a circular archipelago in the Maldives, inside the administrative division of Baa Atoll, which is the southern part of Maalhosmadulu Atoll. Baa Atoll was named a biosphere reserve by UNESCO in 2011. The whole is approximately 38 km by 46 km, covering a surface of 1,127 km. However, the atoll shelters only 5.5 km of emerged land, consisting of sandy islands not higher than 3.19 m, and of which half do not exceed an area of 10 hectares. The administrative subdivision of Baa,