By Valerie Perini

As rising levels of atmospheric carbon dioxide dissolve into seawater, the world’s oceans are becoming more acidic—a trend that is expected to continue over the coming centuries. This ‘ocean acidification’ is just one of the many challenges facing marine life.  Thus, efforts to understand how changing ocean chemistry may interact with other stressors, such as rising ocean temperatures, to impact ocean organisms are becoming increasingly important. In support of these efforts, a new study by MSC Associate Professor Justin Ries investigates the impact of ocean acidification and warming on the spine composition of the tropical sea urchin Echinometra viridis.

In the study, appearing in the journal Chemical Geology, Ries and co-author Travis Courtney of the University of North Carolina raised sea urchins in controlled laboratory experiments under two temperature treatments to mimic winter and summer temperatures and at two seawater carbon dioxide levels to simulate current and predicted-end-of-century levels. The researchers then measured the oxygen and carbon isotope compositions of the urchin spines and culture solutions to determine the impact of the different environmental conditions on the urchins’ isotopic composition.

The researchers found that both oxygen and carbon isotopes in the urchin spines were impacted by temperature, with oxygen isotopes exhibiting a much stronger response than the carbon isotopes. Carbon isotopes, on the other hand, were strongly impacted by atmospheric carbon dioxide.

These results indicate that oxygen and carbon isotopes in urchin skeletons record past seawater temperatures and carbon dioxide levels, respectively.  Since urchins are particularly well preserved in the fossil record, these findings suggest that fossil urchins are a potentially valuable archive of ancient oceanic conditions.