Increasing Carbon Dioxide Threatens Coral Reefs

The team found no evidence that reef organisms are able to acclimate 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 Earth ecosystem," says Langdon, whose research will be published in the June edition of Global Biogeochemical Cycles, an American Geophysical Union journal that covers global environmental change.

Langdon's team is investigating the impact of changing seawater chemistry on coral reef calcification rates. By mid-century, increasing levels of atmospheric carbon dioxide, caused primarily by the burning of fossil fuels, are expected to reduce by 30 percent the carbonate ion concentration of the surface ocean. When Langdon changed the carbonate concentration in the Biosphere 2 ocean to that projected level, he observed significant reduction in calcification rates for the coral and coralline algae.

Langdon believes the results of his research have some 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 near Oracle, Arizona. The 700,000-gallon aquarium of artificial seawater with its community of coral reef life mimics key aspects of real world coral reef ecosystems. Biosphere 2 President and Executive Director William Harris says the ability to control precisely the chemical environment and accurately measure changes in the system offers a unique opportunity to conduct research of this kind.