How does rising atmospheric CO2 affect marine organisms?

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Microzooplankton in an Acidifying Arctic Ocean
Aberle, N., Schulz, K.G., Stuhr, A., Malzahn, A.M., Ludwig, A. and Riebesell, U. 2013. High tolerance of microzooplankton to ocean acidification in an Arctic coastal plankton community. Biogeosciences 10: 1471-1481.

The authors write that "the predicted drop in pH, in the following referred to as 'ocean acidification (OA),' is considered to affect a variety of biological and biogeochemical processes in the oceans with potentially far-reaching consequences on the community and ecosystem level," citing Riebesell et al. (2007); and they say that they "wanted to test whether Arctic coastal plankton communities will be in any way affected by high pCO2/low pH and thus susceptible to ocean acidification."

What was done
To investigate the impact of OA on a natural Arctic plankton community, Aberle et al. state that "a mesocosm experiment was conducted in Kongsfjorden, Svalbard, over a period of about one month in June/July 2010," where nine polyethylene mesocosms were deployed and moored, and where CO2-enriched seawater was injected into them to achieve three different degrees of CO2 equilibrium concentrations - low (175-250 ppm), intermediate (340-600 ppm) and high (675-1085 ppm) - and where 13 days later, nutrients were added to all three mesocosm treatments to ensure a sufficient nutrient supply for bloom development."

What was learned
The six scientists report that they "found almost no direct effects of OA on microzooplankton composition and diversity," and that "both the relative shares of ciliates and heterotrophic dinoflagellates as well as the taxonomic composition of microzooplankton remained unaffected by changes in pCO2/pH."

What it means
In the concluding paragraph of their paper, Aberle et al. state that their hypothesis that a high CO2 concentration would alter microzooplankton community structure, carrying capacity or phenology must be rejected on the basis of their mesocosm experiment, while noting that the findings of their study point to "a relatively high robustness of microzooplankton towards elevated CO2 in coastal waters."

Riebesell, U., Schulz, K., Bellerby, R., Botros, M., Fritsche, P., Meyerhofer, M., Neill, C., Nondal, G., Oschlies, A., Wohlers, J. and Zollner, E. 2007. Enhanced biological carbon consumption in a high CO2 ocean. Nature 450: 545-548.

Reviewed 23 October 2013