Coral reefs are undoubtedly in crisis. Scientists have documented concerning coral bleaching events, dramatic declines in coral cover, fish and shark populations across the Caribbean over recent decades. But a critical question has remained unanswered: has the way energy flows through reef ecosystems also changed? A new study led by scientists at the Smithsonian Tropical Research Institute (STRI) and published in Nature reveals that it has, profoundly. Food chains on modern Caribbean reefs are 60-70% shorter than they were 7,000 years ago, and individual fish have lost the dietary specialisation that once sustained a complex web of energy pathways.