The gradual acidification of the oceans through increasing absorption of atmospheric carbon dioxide is thought to be potentially bad news for coral reefs. As seawater pH falls, the saturation level of carbonate ions in the water also declines. Since reefs are made up of calcium carbonate (from coral skeletons and other sources) they should be slower to form and faster to fall apart.
That is the thinking, anyway. But given that ocean pH is changing very slowly, and reefs form over millennia, it’s difficult to see any effects in the real world.
There is an area of the eastern Pacific off Central America, however, where the water is more acidic than elsewhere, thanks to the upwelling of carbon-dioxide-rich waters. Coral reefs in this region are poorly developed and tend to erode rapidly.
Derek P. Manzello of the University of Miami and colleagues have analyzed the water chemistry and reef samples from the area. They report in The Proceedings of the National Academy of Sciences that the carbonate saturation level is indeed low and that there is relatively little inorganic calcium carbonate “cement” that helps bind the coral skeletons together.
The region, the researchers say, may serve as a model in further studies to help understand what reef systems elsewhere will encounter in a higher-CO2 environment.
Henry Fountain, The New York Times, 29 July 2008. Article.