Carbon Levels "Threaten Coral"

Researchers in the US suspect rising carbon dioxide (CO2) levels in the atmosphere could reduce coral growth by almost half. The researchers, from Columbia University, are investigating the impact of changing seawater chemistry on coral reef calcification rates. They have found no evidence that reef organisms are able to acclimatize to the impacts of higher CO2 levels. And they say the impacts, which are much greater than previously believed, will expose the coral to further stresses. The team, led by Dr. Christopher Langdon, is conducting its research in the ocean ecosystem constructed at Columbia's Biosphere 2 laboratory near Oracle, Arizona.

The results are to be published in Global Biogeochemical Cycles, an American Geophysical Union journal. The Oracle ecosystem comprises a 700,000-gallon aquarium of artificial seawater, with a community of coral reef life which mimics key aspects of real reef ecosystems. Dr. Langdon says the research suggests that coral growth could be reduced by up to 40 per cent from pre-industrial levels over the next 65 years. He said: "This is the first real evidence that increasing atmospheric CO2 levels have a negative impact on a major Earth ecosystem." By the middle of this century, the team believes, rises in CO2 levels, caused mainly by the burning of fossil fuels, will reduce by 30 per cent the carbonate ion concentration of the surface ocean.

When Dr. Langdon changed the carbonate concentration in the Biosphere 2 tank to the projected level, he observed a significant reduction in calcification rates for the coral and coralline algae. He believes his research has some significant implications, for example over the role of reefs as natural breakwaters which can give protection against beach erosion. Dr. Langdon is also concerned that reefs stressed by higher CO2 levels, which could be beneficial on land, will be more vulnerable to other threats, like over-fishing or pollution. He said: "While some terrestrial ecosystems may actually benefit from elevated CO2 levels, that does not appear to be the case for shallow marine ecosystems like a coral reef."