Aldabra Atoll
The atoll is comprised of four large coral islands which enclose a shallow lagoon; the group of islands is itself surrounded by a coral reef. Due to difficulties of access and the atoll's isolation, Aldabra has been protected from human influence and thus retains some 152,000 giant tortoises, the world's largest population of this reptile.
The atoll is comprised of four large coral islands which enclose a shallow lagoon; the group of islands is itself surrounded by a coral reef. Due to difficulties of access and the atoll's isolation, Aldabra has been protected from human influence and thus retains some 152,000 giant tortoises, the world's largest population of this reptile.
Outstanding Universal Value
Brief synthesis
Located in the Indian Ocean, the Aldabra Atoll is an outstanding example of a raised coral atoll. Due to its remoteness and inaccessibility, the atoll has remained largely untouched by humans for the majority of its existence. Aldabra is one of the largest atolls in the world, and contains one of the most important natural habitats for studying evolutionary and ecological processes. It is home to the largest giant tortoise population in the world. The richness and diversity of the ocean and landscapes result in an array of colours and formations that contribute to the atoll's scenic and aesthetic appeal.
Criterion (vii): Aldabra Atoll consists of four main islands of coral limestone separated by narrow passes and enclosing a large shallow lagoon, providing a superlative spectacle of natural phenomena. The lagoon contains many smaller islands and the entire atoll is surrounded by an outer fringing reef. Geomorphologic processes have produced a rugged topography, which supports a variety of habitats with a relatively rich biota for an oceanic island and a high degree of endemism. Marine habitats range from coral reefs to seagrass beds and mangrove mudflats with minimal human impact.
Criterion (ix): The property is an outstanding example of an oceanic island ecosystem in which evolutionary processes are active within a rich biota. Most of the land surface comprises ancient coral reef (~125,000 years old) which has been repeatedly raised above sea level. 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. The top of the terrestrial food chain is, unusually, occupied by an herbivore: the giant tortoise. The tortoises feed on grasses and shrubbery, including plants which have evolved in response to its grazing patterns. The atoll's isolation has also allowed the evolution of endemic flora and fauna. Due to minimal human interference, these ecological processes can be clearly observed in their full complexity.
Criterion (x): Aldabra provides an outstanding natural laboratory for scientific research and discovery. The atoll constitutes a refuge for over 400 endemic species and subspecies (including vertebrates, invertebrates and plants). These include a population of over 100,000 Aldabra Giant Tortoise. The tortoises are the last survivors of a life form once found on other Indian Ocean islands and Aldabra is now their only remaining habitat. The tortoise population is the largest in the world and is entirely self-sustaining: all the elements of its intricate interrelationship with the natural environment are evident. There are also globally important breeding populations of endangered green turtles, and critically endangered hawksbill turtles are also present. The property is a significant natural habitat for birds, with two recorded endemic species (Aldabra Brush Warbler and Aldabra Drongo), and another eleven birds which have distinct subspecies, amongst which is the White-throated Rail, the last remaining flightless bird of the Western Indian Ocean. There are vast waterbird colonies including the second largest frigatebird colonies in the world and one of the world's only two oceanic flamingo populations. The pristine fringing reef system and coral habitat are in excellent health and distinguished by their intactness and the sheer abundance and size of species contained within them.
Integrity
The property includes the four main islands which form the atoll plus numerous islets and the surrounding marine area. It is sufficiently large to support all ongoing biological and ecological processes essential for ensuring continued evolution in the atoll. The remoteness and inaccessibility of the atoll limit extensive human interference which could otherwise jeopardize ongoing processes. As such, Aldabra displays an almost intact ecosystem, sustaining naturally viable populations of all key species.
Protection and management requirements
The property is legally protected under national legislation and is managed by a public trust, the Seychelles Islands Foundation, with daily operations guided by a management plan. Boundaries are ecologically viable but the extension of the seaward boundary some 20 km into the sea would provide additional protection to the marine fauna. While the remoteness of the property has limited human interference, thus contributing for the protection of the biological and ecological processes, it also poses tremendous logistical challenges. Tourism is limited and carefully controlled. Whilst the property displays an almost intact ecosystem, protection and management need to address the constant threats posed by invasive alien species, climate change and oil spills, particularly in the event that oil exploration increases in the wider region.
Long Description
The least-disturbed large island in the Indian Ocean, Aldabra is of outstanding scientific interest. It is the only place in the world where a reptile is the dominant herbivore; some 150,000 giant tortoises (more than on the Galápagos Islands) feed on tie grasses and shrubbery, including plants that have evolved to take advantage of tortoise grazing patterns. The tortoises are the last survivors of a life form once found on many Indian Ocean islands; slow-moving and vulnerable, the giant land tortoises on all other Indian Ocean islands have been driven to extinction by human exploitation, leaving Aldabra as their only remaining stronghold. The island's isolation has allowed the evolution of a distinct fauna, with two endemic birds (Aldabra arush warbler and Aldabra drongo) and another 11 birds that have distinct subspecies (showing evolution in action); among the most interesting is the Aldabran white-throated rail, the last representative of the western Indian Ocean flightless birds - all others have gone the way of the dodo.
Aldabra is a classic coral atoll which has been built up from the seabed. It consists of four main islands of coral limestone separated by narrow passes and enclosing a large shallow lagoon. Most of the land surface consists of ancient coral reef (about 125,000 years old) now raised above sea level, the rest being even older reef limestones. The lagoon contains many smaller islands and the entire atoll is surrounded by an outer reef. Geomorphological processes have produced a varied topography, generally rugged, which supports a variety of habitats with a relatively rich biota for an oceanic island, and a high degree of endemism. Over much of the surface of the islands, weathering has led to dissection of the limestones into holes and pits, although at the eastern end the surface is more continuous on upraised lagoonal sediments. Along the coast are undercut limestone cliffs, with a perched beach and sand dunes on the southern (windward) coast. Marine habitats range from coral reefs to mangrove mudflats with minimal human impact. Tidal range is more than 3 m, which can lead to strong channel currents.
The terrestrial flora is exceptionally rich for a small coral island, with 273 species of flowering plant and fern. Much of the land is covered with dense Pemohis acidula thicket and other shrubs. There are 19 endemic species, a further 22 species are shared only with neighbouring islands. Many of these plants are considered to be threatened. Mangroves surround the lagoon, and inshore waters also support seagrass meadows.
This island group is one of the few areas of the world where reptiles dominate the terrestrial fauna, with the largest world population of giant tortoise, which appears to be self-sustaining. Green turtle breed here, with approximately 1,000 females laying annually. There are 13 species of terrestrial bird including the last representative of the western Indian Ocean flightless birds - Aldabran rail with two endemic Aldabran forms. The Aldabra warbler has not been seen for several years and might be naturally extinct. Previously restricted to 10 ha of coastal tall scrub, this was considered possibly the most endangered bird in the world, as only five birds have been seen since its discovery in 1968. Aldabran drongo and some endemic subspecies are also found. There is a population of about 8,000 birds of this flightless race, which does not seem seriously threatened by the feral cats. The islands are important breeding grounds for thousands of seabirds, including several thousand each of red-tailed tropic bird and white-tailed tropic bird, hundreds of masked booby, several thousand red-footed booby, some Abbott's booby, and thousands each of greater frigate bird and lesser frigate bird. There are also thousands of nesting terns. The only endemic mammal is a flying fox. So far about 1,000 species of insect have been recorded, many' of them new and endemic forms.
There is no permanent settlement. The resident population is composed of Foundation employees and visiting scientists.
Source: UNESCO/CLT/WHC
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