Aldabra Atoll In Seychelles is the important seascape. Aldabra Atoll, 1,150 km southwest of Mahe, is the largest raised coral atoll in the world, encompassing more than a dozen islands bordering a vast lagoon.The atoll’s islands nurture an array of both unique flora and fauna, as well as the world’s largest population of 150,000 giant tortoises. Its lagoon boasts the most vibrant marine life of the entire archipelago.