First around Fiji, then the Florida Keys, then Australia’s Great Barrier Reef, and now in the Indian Ocean. In the past year, anomalous ocean temperatures have left a trail of devastation for the world’s corals, bleaching entire reefs and threatening widespread coral mortality — and now, scientists with the National Oceanic and Atmospheric Administration and International Coral Reef Initiative say the world is experiencing its fourth global bleaching event, the second in the last decade. At least 53 countries and local regions have experienced mass bleaching across the Atlantic, Pacific and Indian oceans. Bleaching — which occurs when stressed coral turn white after expelling symbiotic algae that provide food and color — must be confirmed within each ocean basin to be declared a global bleaching event.

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