How does rising atmospheric CO2 affect marine organisms?

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Elevated CO2 and Warming: Not Always Detrimental
Gooding, R.A., Harley, C.D.G. and Tang, E. 2009. Elevated water temperature and carbon dioxide concentration increase the growth of a keystone echinoderm. Proceedings of the National Academy of Sciences, USA: 10.1073/pnas.0811143106.

What was done
The authors measured growth rates and feeding rates of juvenile sea stars (Pisaster ochraceus) maintained in 246-liter aquaria that were filled with re-circulating natural sea water maintained at temperatures ranging from 5 to 21C, and which were constantly bubbled with either ambient air of 380 ppm CO2 or CO2-enriched air of 780 ppm CO2.

What was learned
Gooding et al. report that "the relative growth (change in wet mass/initial wet mass) of juvenile P. ochraceus increased linearly with temperature from 5C to 21C," and that it also responded positively to atmospheric CO2 enrichment. More specifically, they state that "relative to control treatments, high CO2 alone increased relative growth by 67% over 10 weeks, while a 3C increase in temperature alone increased relative growth by 110%." They also state that increased CO2 "had a positive but non-significant effect on sea star feeding rates, suggesting CO2 may be acting directly at the physiological level to increase growth rates." Last of all, their data show that the percentage of calcified mass in the sea stars dropped from approximately 12% to 11% in response to atmospheric CO2 enrichment at 12C, but that it did not decline further in response to a subsequent 3C warming at either ambient or elevated CO2.

What it means
The three Canadian researchers say their findings demonstrate that "increased CO2 will not have direct negative effects on all marine invertebrates, suggesting that predictions of biotic responses to climate should consider how different types of organisms will respond to changing climatic variables." Indeed, they clearly state -- and without equivocation -- that "responses to anthropogenic climate change, including ocean acidification, will not always be negative," as is also indicated by the results of numerous studies archived under the headings of Calcification and Marine Biota in our Subject Index.

Reviewed 19 August 2009