Wall Street isn’t alone in suffering a steep downturn. A large-scale study in Australia’s Great Barrier Reef has revealed that the rate at which corals absorb calcium from seawater to calcify their hard skeletons has declined precipitously in the past 20 years, slowing coral growth. The report, on page 116, provides empirical data that fuels concerns that increased carbon dioxide in the air is putting these diverse marine ecosystems at risk (Science, 4 May 2007, p. 678). “This study has provided the first really rigorous snapshot of how calcification might be changing” as the ocean temperature and acidity rise, says marine biologist Ove Hoegh-Guldberg of the University of Queensland in Australia. “The results are extremely worrying.”
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Pennisi E., 2009. “CORAL REEFS: Calcification Rates Drop in Australian Reefs.” Science 323 (5910): 27. Full article (subscription required).
A paragraph of this article reads:
“However, the role of acidification in this decline is far from settled. In the laboratory, Alina Szmant, a coral physiological ecologist at the University of North Carolina, Wilmington, and her colleagues found that neither low pH nor a lowered calcium carbonate concentration (which results from increased acidity and is considered key to calcification) slowed coral growth. Instead, calcium bicarbonate proved key, her team reported at ICRS. She faults previous lab studies because they used hydrochloric acid, not carbon dioxide, to lower the pH of the water in the calcification studies. Hydrochloric acid and carbon diox- ide have different effects on seawater chemistry and bicarbonate concentration, she says. Her conclusion: “It’s not clear that carbon dioxide enrichment will have negative effects on calcification rates.”
This is incorrect as many perturbation experiments carried out on corals did use gas bubbling rather than acid addition. All of them indicate a decline of coral calcification at elevated pCO2.