ALDABRA, the collective name of a group of islands in the Indian Ocean, forming part of the British colony of Seychelles. They lie in 9° 30′ S., 46° E., are 265 m. N.W. of the northern point of Madagascar and 690 m. S.W. of Mahé, the principal island of the Seychelles archipelago. The Comoro Islands lie 220 m. S. by W. of Aldabra. The Aldabra Islands constitute an atoll consisting of an oval ring of land, some 40 m. in circumference and about 112 m. broad, enclosing a shallow lagoon. Channels divide the ring into four islands. Grande Terre or South Island forms three-fifths of the circumference. The other islands are West Island or Ile Picard, Polymnie and Middle Island. There are in addition several islets in the lagoon, the most important being Ile Michel. The total land area is estimated at about 60 sq. m., the lagoon, 16 m. long and 4 m. wide, covering a somewhat larger area. Pop. (1906) 127. The islands rise from 20 to 80 ft. above the sea, and consist of rugged coral rock and limestone, there being very little soil. The sea-face is generally overhanging cliff, but in a few places are sandy beaches and low sandhills. Dense scrub covers most of the land, but the inner (lagoon) shore is everywhere bounded by mangrove swamps. The flora and fauna of the islands present features of unusual interest. They are chiefly noted as the habitat of the gigantic land tortoise (Testudo elephantina), now carefully preserved, and of several rare and peculiar birds, including a rail (Dryolimnas aldabranus), an ibis (Ibis abbottii) and a dove (Alectroenas sganzini). Crustacea are abundant. They include oysters, crabs of great size, and a small mussel, found in enormous numbers. The flora includes mangroves, Rubiaceae, Sapotaceae and other forms requiring more than pure coralline material for their growth. Writing of the fauna and flora generally, Mr R. Dupont, curator of the Botanic station at Mahé, who visited Aldabra in 1906, says: “The specimens represented, besides being partly peculiar, mostly belong to the Mascarenes, Madagascar and Comoros species. Many species are also common to East Africa and to India. . . . The predominant species are Madagascar plants and birds, which are carried by the currents and the winds. . . . There are comparatively few (10) species of plants which are endemic as far as the flora has been investigated, and it is probable that most of them are also existing in the Comoros, where the flora is now well known. . . . Endemic inferior animals and mammals are practically non-existent, except two bats and one scorpion, which are allied to Madagascar species or introduced. The reptiles (tortoises) are also nearly allied to the Mascarenes and Madagascar species which once existed. With regard to birds and land shells the relation is much closer to the Comoros species, and the latter, of which I have collected seven species besides Rachis aldabrae, may serve to point out more than the birds the land connexion of Aldabra with the neighbouring countries.” Aldabra, however, although situated in that region of the Indian Ocean which forms part of the Secondary period, is not a peak of the submerged land. It has been built up from the sunken remains of the old continent by a deposit, in the opinion of Professor A. Voeltzkow, of foraminiferal remains (mostly coccoliths and rhabdoliths). In any case, however Aldabra was formed, there can be no suggestion of its ever having been joined to any other land (Stanley Gardiner). Dupont states that at Aldabra the coral foundation is totally above water. The coral limestone of the atoll has a peculiar vitrified appearance and gives out a ringing sound when struck or simply walked on. The coral is generally reddish, but the colouring ranges from light yellow to chocolate-brown.
Aldabra was visited by Portuguese navigators in 1511. The islands were already known to the Arabs, from whom they get their name. They became in the middle of the 18th century dependencies of the French establishments at Bourbon (Réunion), whence expeditions were made for the capture of the giant tortoises. In 1810 with Mauritius, Bourbon, the Seychelles and other islands, Aldabra passed into the possession of Great Britain. The inhabitants are emigrants from the Seychelles. Goats are bred and coco-nuts cultivated, but fishing is the chief industry. With other outlying islands Aldabra is held under lease from the Seychelles government, the lessees having exclusive trading privileges.
See R. Dupont, Report on a Visit of Investigation to . . . the Aldabra Group of the Seychelles Islands (Seychelles, 1907); Dr Abbott in Proceedings, United States National Museum (Washington, 1894); A. Voeltzkow in Abh. der Senckenbergischen Naturforschenden Ges. vol. xxvi. part iv. (1901); J. S. Gardiner, “The Indian Ocean,” Geo. Journ. Oct. 1906.