Aldabra is the world’s second-largest coral atoll. It is situated in the Aldabra Group of islands in the Indian Ocean that are part of the Outer Islands of the Seychelles.
Uninhabited and extremely isolated, Aldabra is virtually untouched by humans. It has distinctive island fauna including the Aldabra giant tortoise (Aldabrachelys gigantea). It consists of four islands around a large shallow lagoon, encircled by fringing coral reef. The atoll reflects both fossil and geomorphological features, the former is the source of the biodiversity seen today. The atoll has the largest population of giant tortoises in the world (about 100,000 animals). Sir David Attenborough called Aldabra “One of the wonders of the world”, and it is also known as one of “crown jewels” of the Indian Ocean. Aside from its vast population of tortoises, it is also the largest raised coral reef in the world with an elevation of 26 feet (7.9 m); and the second largest atoll in the world after Kiritimati Atoll. Aldabra has a large population of the world’s largest terrestrial arthropod, the coconut crab; and hosts the white-throated rail, the only surviving flightless rail species in the Indian Ocean.
Designated by UNESCO as a World Heritage Site in 1982, it is one of the two UNESCO World Heritage Sites in the Seychelles ; both are administered by the Seychelles Islands Foundation (SIF). BirdLife International declared Aldabra as an Important Endemic Bird Area in 2001 on account of its large seabird colonies. Aldabra became a Ramsar Wetland Site of International Importance in 2010. In 2014 Aldabra was designated as a site under the Indian Ocean South East Asia (IOSEA) turtle network.
Historically, the name Aldabra was Al-Hadra or Al-Khadra (with several variants), given by Arab seafarers for “the atoll’s harsh, sun-baked environment”; this name was included in the Portuguese maps of the 16th century. They had named the Indian Ocean as Bahr-el zanj. It was visited by Portuguese navigators in 1511. The islands were already known to the Persians and Arabs, from whom they got their name. In the middle of the 18th century, they became dependencies of the French colony of Réunion, from where expeditions were made for the capture of the giant tortoises. As there are no surface freshwater sources on Aldabra, the interests of the explorers (no proof of any explorer’s visit prior to 1742) was only to exploit the species of tortoise, turtle and fish, and not to inhabit the atoll.
Admiral W.J.L. Wharton of the British navy landed in Aldabra in 1878 to conduct hydrographic surveys of the islands. A decade later the first settlement was established after the Concession was granted by the Seychelles authorities in 1888. A small settlement was established on Ile Picard facing west near the beach. The intention was to exploit and export the natural resources of the islands. As part of the settlements, in the middle of the badamier trees, a chapel built with timber and steel was also established as an essential addition to the plantation houses and office buildings. As Aldabra had no water resources, large rectangular-shaped water storage structures were built adjoining each of the houses. A two-roomed jail was also part of this establishment, a remnant of which is still seen at Aldabra. The exploitation of tortoises for commercial purposes at that time is borne out by the remnants of a crushing mill near Picard, which was used to crush bones of tortoises, which were also brought from other islands in the atoll. Efforts made to grow plantation crops of coconuts, cotton, and sisal failed due to inadequate water sources on the atoll; relics of these plantations are still found on some of the islands.
Around the rim of the lagoon are the larger islands of Ile Picard (West Island), Polymnie, Malabar Island (Middle Island) and Grand Terre (South Island). Goats were introduced in the late 19th century as a food source for the few inhabitants (about 200) living there. Ship rats were introduced and recorded before 1870, and house geckos were noted from the 1970s.
In 1810, with Mauritius, Réunion, the Seychelles and other islands, Aldabra passed into the possession of Great Britain. Réunion was later returned to France, and Mauritius gained possession of Aldabra as well as the rest of the Seychelles. The previous inhabitants were emigrants from the Seychelles. Sailors landed on the atoll in the 19th century and attempted to raid the island for tortoises as food; in 1842, two ships were reported to have taken 1200 of them. By 1900, the tortoises were nearly extinct, and a crew would often have to hunt for three days to find one.
In the early 1800s, concessions given to individuals almost destroyed the forests and tortoise habitats in many islands in Seychelles; on Aldabra Atoll, in view of its remoteness and rugged topography, only small areas of forests were cleared for agricultural operations (mostly coconut plantations) but the tortoises were intensely captured for meat and trade. However, James Spurs, who had the concession of the atoll, was responsible initially for saving the tortoises on the atoll when he banned killing them in 1891.
Following World War II, exploitation of Aldabra for commercial use came to an end and restrictions were even imposed on the number of people who could stay on the islands; this number was fixed at 200 at a time. Introduction of invasive species was banned, faunal species were protected under law, and active research on the ecology and biodiversity of the atoll was undertaken by the Royal Society of London from the middle of the 1970s.
Aldabra, along with Desroches and Farquhar, was part of the British Indian Ocean Territory from 1965 until Seychelles’ independence in 1976. In the 1960s, as a part of their ‘Ocean Island Policy’, and to support East of Suez commitments, the British government considered establishing a RAF base on the island and invited the United States to help fund the project in return for shared use of the facility and a settlement of 11 million dollars. Simultaneously (mid-1960s), the British Broadcasting Corporation became interested in Aldabra as a possible site to locate transmitters with which to rebroadcast the BBC Overseas Service (BBC) into the African mainland. The BBC mounted a fact-finding expedition (Expedition Turtle) to assess its suitability for this purpose. The BBC were dependent upon the RAF for developing the atoll as without this their own ambitions would not have been feasible. After an international protest by scientists (known as ‘the Aldabra Affair’), however, the military plans were abandoned and the atoll instead received full protection. The “Environmental lobbyists” under the leadership of Julian Huxley, with the support of the MP Tam Dalyell, got the British venture torpedoed. In 1966, the Minister of Defence Dennis Healy of the British Government had observed that: “As I understand it, the island of Aldabra is inhabited – like Her Majesty’s Opposition Front bench – by giant turtles, frigate birds and boobies.”
Subsequent to the thwarting of plans to establish a military station at Aldabra(which instead focussed on Diego Garcia in the Chagos Islands), the Royal Society of London resumed their scientific study of the flora and fauna of the atoll with Professor David Stoddart as the leader. The Royal Society bought the lease of the atoll in 1970 and their research station became functional from 1970. After completion of their assigned work, the Royal Society left and the Seychelles Island Foundation (SIF), a public trust of Seychelles, took over the management and protection of the atoll in 1979. SIF functions under the patronage of the President of Seychelles and Aldabra was declared a Special Nature Reserve in 1981, and a year later it became a UNESCO World Heritage Site on 19 November 1982. A brass plaque inscribed with the citation “Aldabra, wonder of nature given to humanity by the people of the Republic of Seychelles” is stationed on the atoll. This appreciation befits the atoll which is truly one of the greatest ecologically undisturbed raised coral atolls in the world.
Aldabra, listed as “Aldabra Atoll”, was designated a UNESCO World Heritage Site on 19 November 1982, and is managed and protected by the Seychelles Islands Foundation. The marine protected area extends 1 kilometre (0.62 mi) into the sea to ensure preservation of its marine fauna. Eco tourism is controlled and introduction of invasive species is restricted. Based on the evaluation process, UNESCO inscribed the site, a legally protected special reserve of 35,000 hectares (86,000 acres), on the list of World Heritage Sites under three criteria: Criterion (vii) Aldabra Atoll encompasses a large expanse of relatively untouched natural beauty where a number of important animal species and some plant species thrive, along with remarkable land formations, and its process provides a unique spectacle of natural phenomena; Criterion (ix): The atoll is a superlative example of an oceanic island ecosystem in which evolutionary processes are active within a rich biota. The size and morphological diversity of the atoll has permitted the development of a variety of discrete insular communities with a high incidence of endemicity among the constituent species that are typical of island ecosystems. The natural processes take place with minimal human interference and can be clearly demonstrated in their full complexity; and Criterion (x): Aldabra provides a natural laboratory for the study of the process of evolutionary ecology and is a platform for key scientific discovery. The atoll constitutes a refuge harbouring viable populations of a range of rare and endangered species of plants and animals. These include the last giant tortoise and flightless bird populations of the Western Indian Ocean, a substantial marine turtle breeding population, and large seabird colonies which number in the tens of thousands. The substantial tortoise population is self-sustaining and all the elements of its inter-relationship with the terrestrial environment are evident.
BirdLife International declared Aldabra as an Important Bird Area (IBA) in 2001 on account of its large seabird colonies under categories A1, A2, A4i, A4ii and A4iii, covering an area of 33,180 hectares (82,000 acres) overlapping with the special reserve area of 35,000 hectares (86,000 acres) of Aldabra Atoll.
Covering 25,100 ha (over half the area of the whole atoll) the wetland ecosystem of Aldabra was listed as a Wetland of International Importance under the Ramsar Convention in 2010. These wetlands at Aldabra include the extensive shallow lagoon inside the atoll, which is carpeted with lush seagrass beds and patchy coral reefs, the intertidal mud flats, the coral reefs outside the lagoon (see next section), freshwater pools, beaches, and 2000 ha of mangrove stands. These wetlands support several endangered species including the increasing number of turtles at the atoll, dugongs and many other bird, fish and invertebrate species.