A little good news on the climate change front, for a change: some marine organisms may be able to adapt surprisingly well to ocean acidification caused by carbon dioxide from burning fossil fuels.

As the oceans become more acidic, many marine animals will have a harder time extracting the calcium from seawater that they need to build their skeletons. Marine biologists fear an ecological catastrophe could be imminent unless animals evolve to take up calcium more efficiently.

Melissa Pespeni, an evolutionary biologist at Indiana University in Bloomington, and her colleagues decided to find out to what extent evolution can keep pace with the changing environment. In their lab, they reared larvae of the purple sea urchin in water of normal or elevated acidity, corresponding to atmospheric CO₂ levels of 400 and 900 parts per million. To their surprise, they found that the more acidic water had no apparent negative effect on the development of the larval skeletons.

Behind that apparent stability, though, was a lot of genetic change. When Pespeni used gene sequencing to study the developing larvae, she found that gene frequencies had shifted dramatically during that time. In particular, genes related to growth, lipid metabolism and the movement of ions into and out of cells showed significantly more changes in urchins reared under high-acidity conditions. All these types of genes help cells cope with increased acidity – a strong hint that the changes are the result of natural selection.

“If there’s any organism we would expect to be able to adapt to something like this, it would be the purple sea urchin, because they have evolved in such a variable environment,” says Pespeni. The urchins live on the Pacific coast of North America, where they often experience upwellings of CO₂-rich water from the deep ocean.

Earlier studies had shown that the urchins had unusually high levels of genetic variability. Pespeni’s new study shows that evolution can rapidly select the gene variants needed to adapt to more acid conditions, saysJennifer Sunday, a climate change ecologist at Simon Fraser University in Burnaby, Canada.

Last year, researchers in Germany reported similar adaptation to acid conditions in a single-celled alga. It remains to be seen, however, whether other species can evolve quickly enough to cope with ocean acidification. Most likely some will and others will not, says Sunday, “so we’re looking at a future ocean that could be quite different”.

Journal reference: PNAS, DOI:10.1073/pnas.1220673110