Coral Face Death From Above

By Elizabeth Pennisi
ScienceNOW Daily News
5 July 2006

As worried as many researchers are about carbon dioxide's effects on global climate change, a cadre of oceanographers and marine biologists are most concerned about what the greenhouse gas is doing to the oceans. Since the industrial revolution, the oceans have absorbed 142 billion metric tons of carbon dioxide, enough to increase the water's acidity by 30% and to threaten coral and other organisms that depend on dissolved carbonate to build their skeletons, according to a U.S. government report released today.

Analyses of ice cores have shown that the ocean's chemistry has been stable for about 650,000 years. But in the past 150 years, excess carbon dioxide dissolving into the water has caused the average ocean pH to drop from 8.2 to 7.9. This change has decreased the concentration of carbonate ions, which corals, planktonic marine snails called pteropods, and other marine organisms need to make calcium carbonate shells and skeletons. Laboratory studies have shown that the fewer the number of carbonate ions, the slower these organisms grow. And if the pH gets too low, these shells may start to dissolve, says Joan Kleypas a marine ecologist from the National Center for Atmospheric Research in Boulder, Colorado, and a co-author of the report. Eventually, reefs could shrink, and pteropods--a key food for juvenile salmon and other fish--could disappear, she warns.

The new report is a joint product of the National Science Foundation, the U.S. Geological Survey, and the National Oceanic and Atmospheric Administration, which sponsored a 2005 workshop to assess these changes. The resulting 96-page document, "Impacts of Ocean Acidification on Coral Reefs and other Marine Calcifiers," compiles existing data on acidification and lays out a plan of action for the international oceanographic community. The problem "needs some pretty immediate attention," Kleypas told reporters at a teleconference today.

The North Pacific seems to be the most vulnerable, she and her colleagues report. There's 10% more carbon dioxide there than in the Atlantic, and the depth at which water becomes "corrosive" to calcium-carbonate organisms is shallower. The transition depth off Alaska is just 85 meters. By the end of the century, that depth is predicted to be shallow enough that cold water corals there could be in water that dissolves them. With time, the tropics, and the rest of the world's reefs, could be similarly affected.

The report calls for more research on the effects of reduced calcification on the organisms involved, on if and how organisms can adapt to the changing pH, and on what impact these effects will have on marine ecosystems. Large-scale, long-term, international studies are essential, Kleypas and her colleagues note.

Such studies, "are going to become extremely important," as the problem worsens, says Robert Byrne a University of South Florida marine chemist based in St. Petersburg. Because these organisms are part of the marine food web, "it's going to be a problem that you are eventually going to have on your dinner plate," he says. "The public needs to know about it."