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Often called the Galapagos of the Indian Ocean, Aldabra Island is one of the few areas in the world where a slow reptile, the giant tortoise, is the dominant land animal. With about 152,000 individuals, Aldabra has the largest population of these giant tortoises in the world. What’s more, this ecoregion is home to the very last known population of flightless birds in the western Indian Ocean, and it provides valuable breeding areas for both marine turtles and seabirds. This ecoregion is also an important refuge for the coconut crab and a vital stronghold for the remaining 100 to 250 pairs of Madagascar sacred ibis. One-fifth of the flowering plants here are endemic.
The rugged landscape of Aldabra Island includes limestone cliffs, coastal beaches, and sand dunes. Most of the surface of the island is the remains of an ancient coral reef. Over some 125,000 years, weathering has eroded the ancient limestone into pits and holes on much of the island’s surface. Four coral limestone islands form a ring around a large central lagoon, forming the world’s largest atoll. The islands are separated by narrow passes that lead to the sea, and the shores that face the lagoon support mangroves. Each year there is a wet season from November to April and a drier season from May to November. Occasionally, Aldabra is affected by cyclones.
Small shrubs, known as pemphis, form impenetrable thickets on the higher rocky areas. In flatter areas, a mixture of low trees, shrubs, herbs, and grasses provides the perfect habitat for giant tortoises seeking shade. It is not unusual to see as many as 60 tortoises together under a single shelter, often stacked two deep. The nests of green turtles and hawksbill turtles line the shores, while plump Aldabra white-throated rails, the last living representative of several species of Indian Ocean flightless birds, walk along the flat terrain, searching for edible vegetation. In summer, from November to March, the skies are filled with breeding seabirds such as red-tailed tropic birds, red-footed boobies, and greater and lesser frigate birds gathering food for their young. Several species of terns nest by the thousands on the atoll. Large fruit bats--the only native mammals of this ecoregion--spread seeds in their droppings as they move about in search of fruits. These seeds help regenerate fruit-bearing trees and shrubs throughout the island. At night, the gigantic coconut or "robber" crabs climb coconut trees and snip off the nuts with their large and powerful claws, then descend the tree to feed on the coconut in the safety of their burrow.
Not only is this one of the most isolated ecoregions of the world, but it is also one of the rare ecoregions that has no permanent human inhabitants. Unfortunately, alien animals such as rats, cats, and goats that were brought to the island by visiting humans have done considerable damage to the native wildlife and vegetation. Rats are thought to be one of the major contributing factors to the extinction of the Aldabra warbler in 1983. Another introduced species, the mealy bug, has caused a lot of damage to native vegetation. While populations of turtles and other animals have recovered from past hunting on the island, there is an ongoing illegal export of turtles. For more information on this ecoregion, go to the World Wildlife Fund Scientific Report. All text by World Wildlife Fund © 2001
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