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
Southern Maalhosmadulu Atoll the great frigatebird in the Maldives. Likewise, other marine creatures such as seaturtles and hawksbill turtles can be encountered. The Fisheries Ministry of the Maldives has banned catching turtles or taking eggs from Olhugiri, which also applies to 11 other islands. Southern Maalhosmadulu Atoll Southern Maalhosmadulu Atoll (code name Baa) is an administrative division of the Maldives. It consists of two separate natural atolls, namely the southern part of Maalhosmadulhu Atoll (which is 42 km long and 32 km wide and consists of 10 inhabited islands) and the smaller natural atoll known as Goifulhafehendhu Atoll (Horsburgh Atoll in the Admiralty