Heat And Acidity Ganging Up On Coral

"Human-caused emissions of carbon dioxide are starting to harm marine life with a one-two punch of rising temperatures and stronger ocean acidity. Now a study of a reef in the Red Sea confirms the impact of rising acidity and suggests that it could eventually make reefs across the globe dissolve. "This is a very significant and important result," says Ben McNeil of the University of New South Wales in Sydney. "We are finally moving towards a more complete picture of how coral reefs will respond to a high CO₂ and warmer ocean."

As the atmosphere warms, so does the ocean, and the extra heat can affect the metabolism of corals. Extreme temperatures can lead to so-called bleaching of coral. In addition, according to laboratory studies, these reef-builders and other organisms that construct skeletons out of calcium carbonate are affected by the increasing acidity created when the sea absorbs carbon dioxide.

Now, a study that began with marine geochemist Jacob Silverman's doctoral research at the Hebrew University of Jerusalem, Israel, has made a quantitative link between atmospheric levels of CO₂ and the fate of coral. Currently a postdoc at the Carnegie Institution Department of Global Ecology in Stanford, California, Silverman looked at how nutrients were affecting photosynthesis, respiration, and calcification on the kilometer-long Eilat reef in the Red Sea north of Egypt.

Silverman and his colleagues determined the relationship among the rate of calcification, water temperature, and the concentration of carbonate ions. Corals use these ions to build their skeletons, and the available amount falls with stronger acidity. They also showed how the calcification rate affected the amount of live coral on the reef. The resulting equations, or "rate law," is described in the current issue of Geophysical Research Letters. The group confirmed the equations with measurements from studies done at other reefs from the 1970s to 1990s."

ORIGINAL SOURCE: ScienceNOW