How does rising atmospheric CO2 affect marine organisms?

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The Impacts of Business-As-Usual Projected Altered Temperature, Salinity and pCO2 on Filamentous Cyanobacteria of the Baltic Sea
Karlberg, M. and Wulff, A. 2013. Impact of temperature and species interaction on filamentous cyanobacteria may be more important than salinity and increased pCO2 levels. Marine Biology 160: 2063-2072.

The authors were curious about the ramifications of potential future increases in the air's CO2 content on the productivity of two dominating filamentous cyanobacteria species of the Baltic Sea (Nodularia spumigena and a mix of Aphanizomenon sp.) during the summer bloom of the Baltic Proper; so they decided to experimentally determine their responses to changes in that region's environment that were predicted to occur in response to the IPCC's business-as-usual A1FI scenario described by Meehl et al. (2007): a temperature increase of 4°C, an atmospheric pCO2 increase from 380 to 960 ppm, and a reduction in salinity from 7 to 4.

What was done
Working in the laboratory, Karlberg and Wulff measured numerous responses of the two species of cyanobacteria - growing both separately and together - to different combinations of these various environmental changes.

What was learned
The two researchers report that (1) "increased temperature, from 12 to 16°C, had a positive effect on the biovolume and photosynthetic activity of both species," that (2) "compared when growing separately, the biovolume of each species was lower when grown together," and that (3) "decreased salinity, from 7 to 4, and elevated levels of pCO2, from 380 to 960 ppm, had no effect on the biovolume, but on [the photosynthetic activity] (Fv/Fm) of N. spumigena with higher Fv/Fm in salinity 7."

What it means
Karlberg and Wulff say their results suggest that "the projected A1FI scenario might be beneficial for the two species dominating the extensive summer blooms in the Baltic Proper." But they caution that their results "further stress the importance of studying interactions between species." And they thus conclude by stating that "long-term studies together with multifactorial and mesocosm/field experiments are needed to elucidate the future impact of climate change effects on Baltic filamentous cyanobacteria.".

Meehl, G.A., Stocker, T.F., Collins, W.D., Friedlingstein, P., Gaye, A.T., Gregory, J.M., Kitoh, A., Knutti, R., Murphy, J.M., Noda, A., Raper, S.C.B., Watterson, I.G., Weaver, A.J. and Zhao, Z.-C. 2007. In: IPCC Climate Change 2007: The Physical Science Basis: Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change (Solomon, S., Qin, D., Manning, M., Chen, Z., Marquis, M., Averyt, K.B., Tignor, M. and Miller, H.L., Eds.). Cambridge University Press, Cambridge, United Kingdom, pp. 747-846.

Reviewed 20 November 2013