"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."
Source: UNESCO World Heritage List
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.
Source: UNESCO World Heritage List
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.
