When the coral dies, the entire ecosystem around it transforms. Fish that feed on the coral, use it as shelter, or nibble on the algae that grows among it die or move away. The bigger fish that feed on those fish disappear too. But the cascading effects don’t stop there. Birds that eat fish lose their energy source, and island plants that thrive on bird droppings can be depleted. And, of course, people who rely on reefs for food, income or shelter from waves – some half a billion people worldwide – lose their vital resource.