Carbon dioxide build-up threatens coral reefs

By mid-century, increasing levels of atmospheric carbon dioxide are expected to reduce the carbonate ion concentration of the surface ocean by 30%. When researchers at Columbia University’s Biosphere 2 Center changed the carbonate concentration in the Biosphere 2 ocean to that level they observed a significant reduction in calcification rates for coral and coralline algae. Furthermore, the team found no evidence that reef organisms are able to acclimatise after prolonged exposure to the reduced carbonate levels.

“This is the first real evidence that increasing atmospheric carbon dioxide levels have a negative impact on a major ecosystem,” says the leader of the team, Dr. Christopher Langdon, whose research will be published in the June edition of Global Biogeochemical Cycles.

Langdon believes the results of his research have important implications. Coral reefs are natural breakwaters protecting tropical islands and other coastal areas from beach erosion. “While some terrestrial ecosystems may actually benefit from elevated carbon dioxide levels, that does not appear to be the case for shallow marine ecosystems like a coral reef,” says Langdon. The impacts are much greater than previously believed, leading to increasing vulnerability of many reefs to other man-caused sources of stress, like over-fishing or pollution, he says.

The project is underway in the ocean ecosystem at Columbia’s Biosphere 2 laboratory in Arizona. The 700,000-gallon (2,649,000 litres) aquarium of artificial seawater, with its community of coral reef life, mimics key aspects of real world coral reef ecosystems.