Coral reefs off the Sumatran island of Pulau Weh, Indonesia, before (left) and after a bleaching event triggered by a large pool of warm water swept into the Indian Ocean. Coral reefs in Southeast Asia and the Indian Ocean are dying from the worst bleaching effect in more than a decade. The bleaching is caused by warm water sweeping over the reefs, shocking the corals and causing them to shed the algae which nourish them. If corals fail to regain their algae, they starve to death. The UNEP warns that climate change, if unchecked, could see surface sea temperatures rise by 2100 with important implications for coral reefs and other temperature-sensitive marine organisms

Photograph: ARC Centre Of Excellence/AFP