That foundation is no longer solid. Corals build colonies that secrete calcium carbonate to form ocean reefs. When they’re healthy, coral reefs provide shelter and food for animals all along the food chain, including the top: us. Across the planet, half a billion people rely, directly and indirectly, on corals for their living. That’s why what happens to the 9,000-year-old Great Barrier Reef, as well as to other reefs worldwide, is critical. The recent Queensland floods were most notably tragic for the lives lost and property destroyed. But they have also hurt the Great Barrier Reef by funneling into the ocean vast plumes of freshwater and agricultural runoff that could severely damage the coral.