Coral atolls

The Tuamotu Islands in French Polynesia are the largest chain of coral atolls on the planet. Once high, volcanic peaks, they have eroded completely over millennia leaving only a fringing reef around a central lagoon. Coral rubble and sand have built up in places to form motus, low, palm covered islands. The 78 Tuamotu Islands are spread across a swathe of the Pacific Ocean the size of Western Europe – with just 18,000 inhabitants. (Gabi Mocatta)