The Heat Is Online

CO2 Implicated in Coral Deaths

CARBON DIOXIDE COULD BE KILLING CORAL, STUDY SAYS

April 6, 1999

By Maggie Fox, Health and Science Correspondent

WASHINGTON - Scientists said they had found another potential threat to delicate coral reefs, coming from carbon dioxide dissolved in seawater.

Excess carbon dioxide from burning coal, gas and other fossil fuels has long been blamed for helping raise global temperatures through the greenhouse effect, and such higher temperatures have been blamed for helping kill coral reefs.

Joan Kleypas of the National Centre for Atmospheric Research in Boulder, Colorado, and colleagues in France, Australia, Kansas and California, found that the excess carbon can also dissolve in the ocean and disrupt complex chemical reactions that the coral uses to build its reef colonies.

"This does not mean the end of reefs," Kleypas said in a telephone interview. "It simply indicates that this could effect some changes in reefs over the next 50 to 100 years. We just don't know what those effects are yet."

Coral reefs are a cornerstone of ocean life. Corals are tiny, soft-bodied organisms that form huge colonies that gradually build up into into rock-like growths as generations of the animals die and skeletonize.

There is much evidence that coral reefs, which shelter a huge variety of sea life, are starting to die off all over the world. Changes in ocean temperatures, pollution, and physical assaults by boat anchors are all key factors in the decline.

But the chemical balance of the sea is also important, Kleypas's team found.

Coral uses carbon in the form of carbonate, which it combines with calcium to make its skeleton. "It's like the way we would form bone," Kleypas, a marine scientist, said.

"If you think of adding carbon dioxide to water - and that's what we are doing (by burning fossil fuels) - we are driving more carbon dioxide into the surface of the water, that makes carbonic acid" she said.

This carbonic acid uses up more of the carbon that should be available to the coral, depriving it of the carbonate it needs.

"It's counterintuitive - you'd think if you are adding carbon dioxide to water there would be more carbonate available, but because you are forming an acid you are shifting that carbon away from the carbonate ion," she said.

The idea first came from amateur aquarium enthusiasts, who found that when the carbonate balance was off, their coral changed, she said.

Writing in the journal Science. Kleypas and colleagues said careful experiments showed this was indeed the case - adding carbon changed the way coral grows.

"So far all the data show a good correlation between how much calcium carbonate there is in the ocean and how much organisms are laying down in their skeletons," she said.

The effects are not always obvious to the eye. "Sometimes you can't tell the difference by looking at the coral," Kleypas said. "But if you weighed two pieces of coral, one might weigh more than another."

This might in turn weaken the coral, although Kleypas said this has not been demonstrated on a real, living coral reef yet. "There could be changes out there already but we haven't gone out to look at those changes," she said.

"I hope we're wrong," she added. "We really think that the major threats to reefs are still direct human destruction of reefs and overfishing."

(C) Reuters Limited 1999.