Atoll remains of an ancient atoll as a hill in a limestone area is called a reef knoll. The second largest atoll by dry land area is Aldabra with 155 km². The largest atoll in terms of island numbers is Huvadhu Atoll in the south of the Maldives with 255 islands. In 1842, Charles Darwin explained the creation of coral atolls in the southern Pacific Ocean based upon observations made during a five-year voyage aboard from 1831 to 1836. Accepted as basically correct, his explanation involved considering that several tropical island types—from high volcanic island, through barrier reef island, to atoll—represented
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,