Images of corals in white in the waters of the Gulf of Thailand around Koh Tao as coral reefs experience the world's fourth global bleaching event. Coral polyps are animals that depend on an algae to provide most of their food. These algae also generally give the reef its colour. But when the sea is too warm, the polyps expel the algae. The reef turns white and the coral begins to starve. Coral bleaching has been recorded in over 60 countries since early 2023, threatening reefs that are key to ocean biodiversity and support fishing and tourism industries globally. STOCKSHOTS