In the Northern Hemisphere, the summer of 2023 was the hottest on record. In the Caribbean, coral reefs sat in sweltering water for months—stewing in a dangerous marine heat wave that started earlier, lasted longer, and climbed to higher temperatures than ever recorded in some locations. For many Caribbean corals, last year’s heat proved too much to bear. But even now, several months after the water has cooled to temperatures that no longer stress corals.