Coral reefs are havens for marine biodiversity and underpin the economies of many coastal communities. But they are very sensitive to changes in ocean chemistry resulting from greenhouse gas emissions, as well as to pollution, warming waters, overdevelopment, and overfishing. Reefs use a mineral called aragonite, a naturally occurring form of calcium carbonate, CaCO3, to make their skeletons. When carbon dioxide, CO2, from the atmosphere is absorbed by the ocean, it forms carbonic acid—the same stuff that makes soda fizz--making the ocean more acidic and thus more difficult for many marine organisms to grow their shells and skeletons and threatening coral reefs globally.
Ken Caldeira and colleagues have looked at several aspects of coral reef decline. In one study they calculated ocean chemical conditions that would occur under different future scenarios and determined that if we continue on our current emissions path, by the end of the century there will be no areas of the ocean with the chemical properties that have supported coral reef growth in the past. In another study at Australia’s Great Barrier Reef, the researchers found that carbonate accumulation is 44% lower than 40 years ago and that the reef dissolves nearly three times more at night than in the 1970s. They suspect that sea cucumbers are a factor in this nightly activity as they feed.