Bleached coral. The colour in the coral is lost due to the expulsion of symbiotic unicellular algae called zooxanthellae that live within its tissues. In this case, the zooxanthellae have been expelled due to high water temperature. Some of the coral here appears brown as it still contains the zooxanthellae, which is needed to provide the coral with nutrients and thus maintain its colour. Photographed in the Maldives, Indian Ocean.