Aldabra

Aldabra is the world's second-largest coral atoll,^[2] lying southeast of the continent of Africa. It is part of the Aldabra Group of islands in the Indian Ocean that are part of the Outer Islands of the Seychelles, with a distance of 1,120 km (700 mi) southwest of the capital, Victoria on Mahé Island. Initially named by Arab seafarers for its harsh environment, Aldabra became a French colony dependency in the 18th century, leading to the exploitation of its natural resources, particularly giant tortoises. After passing through British hands, Aldabra faced potential military use in the 1960s, but international protests resulted in its protection. The atoll boasts unique geography, featuring the world's largest raised coral reef and a large shallow lagoon. Aldabra's history involves human impact, including failed agricultural ventures. Post-World War II, conservation efforts increased, leading to its inclusion in the British Indian Ocean Territory and eventual independence for Seychelles. Following an international protest by scientists known as the 'Aldabra Affair,' the Royal Society of London and later the Seychelles Islands Foundation conducted research, leading to Aldabra's declaration as a UNESCO World Heritage Site in 1982. The atoll's flora and fauna, notably the giant tortoises, comprise an 'ecological wonder', with Aldabra serving as a critical breeding ground for various species. Conservation challenges, such as invasive species and plastic pollution, persist, but protective measures, including UNESCO designation, underscore Aldabra's significance as a natural vital scientific research site. Aldabra receives limited tourism to safeguard its delicate ecosystem and is accessible primarily through guided tours.

History

The name Aldabra, originally Al-Hadra or Al-Khadra (with several variants), was given by

As there are no surface freshwater sources on Aldabra, the interests of the explorers (no proof of any European explorer's visit prior to 1742) was only to exploit the species of tortoise, turtle and fish, and not to inhabit the atoll.[4] 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.

Admiral W. J. L. Wharton of the British Navy landed in Aldabra in 1878 to conduct hydrographic surveys of the islands.^[8] In 1888, the first settlement was established after the Concession was granted by the Seychelles authorities.^[4][9] A small settlement was established on Picard Island facing west near the beach. The intention was to exploit and export the natural resources of the islands. The villagers built a chapel, in the middle of the badamier trees, using timber and steel; the chapel was considered an essential addition to the plantation houses and office buildings. As Aldabra had no freshwater resources, large rectangular-shaped water storage structures were built adjoining each building. A two-roomed jail was also built in the village, a remnant of which is extant.

The exploitation of tortoises for commercial purposes at that time is illustrated by the remnants of a crushing mill at

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.[11] 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.^[12]

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 mid-1970s.^[9]

Aldabra, along with

After an international protest by scientists (known as 'the Aldabra Affair'),[13] however, the military plans were abandoned and the atoll instead received full protection.^[10] The "Environmental lobbyists" under the leadership of Julian Huxley, with the support of MPs Tam Dalyell and Robin Cook,^[14] got the British venture torpedoed.^[15][16] In 1966, British Defence Minister Denis Healey had observed: "As I understand it, the island of Aldabra is inhabited - like Her Majesty's Opposition Front bench - by giant turtles, frigate birds and boobies."^[17]

Subsequent to the thwarting of plans to establish a military station at Aldabra (which instead focused on

Around the rim of the lagoon are the larger islands of the atoll. The total land area of the atoll is 155.4 square kilometres (60.0 sq mi).[21] The size including the lagoon is 380 square kilometres (150 sq mi). The outside rim of the atoll has three passages which connect to the lagoon, which is 6–10 kilometres (3.7–6.2 mi) in width where it opens to the sea. The water depth in the lagoon averages about 5 metres (16 ft); however, the passages that open to the sea are up to 20 metres (66 ft) deep and strongly affected by tidal currents.

List of islands

Aldabra atoll has, besides the four larger islands, some 40 smaller islands and rocks,

The atoll reflects both fossil and geomorphological features, the former is the source of the biodiversity seen today.^[25] The atoll consists of reef limestone of Pleistocene age (with irregular coral formations called "champignon",^[26] made up of two layers of varying stages of crystallization ^[27]) and this extends over an average width of 2 kilometres (1.2 mi) rising to a height of 8 metres (26 ft) above sea level, and forming the rim line (low cliffs with "deep notches, preceded by jagged pinnacles") of the shallow central lagoon.^{[17][11][25][21]} Geologically the limestone beds have been subjected to striation, sink holes and pits with prominent and continuous limestone bed on the eastern side above the sediment deposits.

The coastline has undercut

Aldabra is situated in the dry zone of the south-west Indian Ocean. The northwest monsoon season is from November to March and brings the heaviest rainfall. In the remaining months, the south-easterly trade winds are dominant. Aldabra receives an annual average rainfall of 960 millimetres (38 in).^[21] Cyclones are rare in the Seychelles due to its nearness to the Equator.^[28] The reported monthly mean maximum air temperature recorded in December is 31 °C (88 °F). The mean minimum temperature recorded in August is 22 °C (72 °F).

The hydrodynamics of Aldabra's lagoon are dominated by the tides. The maximum tidal range at Aldabra is around 2.7m, which is exceptionally large for an atoll. Flow between the lagoon and open ocean is only possible through a small number of narrow channels, generating tidal currents of over 3 m/s at Passe Gionnet, and over 1 m/s at most other channels. Due to the restriction of water exchange through these channels, tides within the lagoon are lagged compared to the open ocean, and the tidal range varies across the lagoon.^[29]

Aldabra sits in the path of the Indian Ocean's westward-flowing South Equatorial Current. Eddies are generated in the wake of Aldabra as the South Equatorial Current passes it, driving upwelling of deep waters that bring nutrients to the surface, and drive phytoplankton growth.^[30]

Wildlife

Left: coral "mushrooms". Right: nesting male great frigatebird.

The earliest study of the flora and fauna, and also the

The higher areas of Aldabra are covered in

The lagoon is bordered by mangrove forests, and has large inland seagrass meadows as well as areas of coral reef and sand flats.^[7] The mangroves, which thrive in tidal mudflat areas and saline conditions, are seen on the shores of the lagoon and are integral to the coastal ecosystem. There are seven species of mangrove on Aldabra, three of which are rarely occurring species. These include 'Mangliye blan' or white mangrove (Avicennia marina) which grows to 12 metres (39 ft), 'Mangliye lat' or black mangrove (Bruguiera gymnorhiza) which grows to 18 metres (59 ft) in a conical shape, 'Mangliye zonn' (Ceriops tagal) which grows to 7 metres (23 ft) with a buttressed trunk, and 'Mangliye rouz' or red mangrove (Rhizophora mucronata) which is the tallest species up to 20 metres (66 ft) in height.^[36]

Fauna

The atoll has distinctive

Alipore Zoological Gardens

on 24 March 2006.

Aldabra is a breeding ground for the

butterflies also flutter around Aldabra.^[43]

Endemic birds include the

Comoros blue pigeon, Malagasy kestrel, Malagasy coucal, Madagascar nightjar, Malagasy bulbul and souimanga sunbird.^{[45][46][47][48]}

At least 13 species of

cetaceans, including dolphins, orcas, and especially humpback whales,^[49][50] have been identified in the waters.^[51][52] Dugongs, thought to be regionally extinct in the 18th century,^[53] have been confirmed multiple times in recent years.^[54][55][56]

Conservation

Conservationists feared a major threat to the atoll's biodiversity in the 1960s when, as part of the British Indian Ocean Territory, the British made plans to set up a military establishment on the atoll. Due to national and international opposition this plan was cancelled in 1967. This incident became known as the 'Aldabra Affair' in England.

Invasive alien species such as

Aldabra also accumulates large amounts of plastic pollution on its coastline and, despite a major clean-up effort in 2019, over 500 tonnes is thought to remain on the atoll, with significant impacts on wildlife.^[57] Most of this pollution originates from the regional fishing industry, although a significant proportion is also transported from southeast Asia through ocean currents.^[58]

The coral reefs at Aldabra were severely affected by the 2016 El Niño event. Although thermal stress was not exceptionally high (less than 4 Degree Heating Weeks), hard coral cover on Aldabra's seaward-facing reefs was reduced by over 50% (35% in the lagoon), and soft coral cover fell by over 90%.^[59] Fortunately, there are some signs of recovery, as the abundance of juvenile corals has since increased significantly, particularly within the lagoon,^[60] although Aldabra's reefs of course remain critically threatened by climate change.

Protection

Aldabra atoll was designated a UNESCO World Heritage Site on 19 November 1982. It is one of the two UNESCO World Heritage Sites in the Seychelles;,^[61] and is managed by the Seychelles Islands Foundation (SIF).^[62] The marine protected area extends 1 kilometre (0.62 mi) into the sea to ensure preservation of its marine fauna.^[7][26] Eco tourism is controlled and introduction of invasive species is restricted.^[7]

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;^[7] 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;^[7] 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 harboring viable populations of a range of rare and endangered species of plants and animals, including 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.^[7][63]

BirdLife International declared Aldabra as an Important Endemic Bird Area (IBA) in 2001 due to 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.^[26][64]

Aldabra became a Ramsar Wetland Site of International Importance in 2010.^[17] Covering 25,100 ha (over half the area of the whole atoll) the wetland ecosystem of Aldabra includes 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, 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.

Aldabra was designated as a site under the Indian Ocean South East Asia (IOSEA) turtle network, in their 2014 convention.

Demography

A small scientific research station of the SIF is based in La Gigi village on Picard Island. The permanent staff (currently 12^[65]) conduct research to study Aldabra's biodiversity.

Transport

Aldabra is not easily accessed. No airstrips, helipads or landing jetties have been permitted on the atoll. The nearest airfield is on Assumption is 50 kilometres (31 mi) south-east of Picard Island. Bi-monthly supply ships operating from Mahé provide essentials to the research station.^[11]

Tourism

Cruises are operated by several companies ^[66][67] along with dive boats which may visit the atoll on expedition tours. Visits to the island by people other than the scientists and staff of the SIF are strictly controlled and only guided tours are provided with prior permission.^[66] As of 2012^[update], a yearly average of 900 tourists visit the atoll. Within the atoll, paved walking paths exist from the village of La Gigi, which leads to a promontory from where scenic views of the large lagoon (during low tides) and the mangrove species are seen.^[66]

Image gallery

• 
  Map 1
• 
  District Map
• 
  Map 2
• 
  Map 3
• 
  Map 4
• 
  NASA photo of Aldabra Atoll
• 
  Aldabra and Assumption Island

References

Bibliography

• Coe, Malcolm James (1998). A Fragile Eden: Portraits of the Endemic Flowering Plants of the Granitic Seychelles. Princeton University Press. pp. 11–.
  ISBN 978-0-691-04817-8
  . Retrieved 23 March 2013.
• Mair, Lyn; Beckley, Lynnath (2012). Seychelles. Bradt Travel Guides. pp. 126–.
  ISBN 978-1-84162-406-8
  . Retrieved 23 March 2013.
• Swingland, Ian Richard; Klemens, Michael W. (1989). The Conservation Biology of Tortoises. IUCN. pp. 105–.
  ISBN 978-2-88032-986-0
  . Retrieved 27 March 2013.

External links

Wikimedia Commons has media related to Aldabra Atoll.

• Aldabra islands
• "Expedition Aldabra" (Gordon, Ethan, Fathoms Online, Issue #8)
• Photos of Aldabran wildlife
• WCMC Natural Site Data Sheet
• Save Our Seas Foundation Promotional Video for Aldabra
• Pictures of Russian Robinson Radio expedition to Aldabra
• Island guide 1 Archived 2020-10-02 at the Wayback Machine
• National Bureau of Statistics
• 2010 Sailing directions
• UNEP World Conservation Monitoring Center: Aldabra fact sheet
• Gallery