How does rising atmospheric CO2 affect marine organisms?

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Responses of Sea-Ice Algae to Projected Ocean Acidification Levels
McMinn, A., Muller, M.N., Martin, A. and Ryan, K.G. 2014. The response of Antarctic sea ice algae to changes in pH and CO2. PLOS ONE 9: e86984.

The authors write that "sea ice microbial communities are a critical component of polar marine ecosystems, contributing 10-50% of the annual primary production of polar seas (Arrigo and Thomas, 2004), supporting overwintering zooplankton species, especially Antarctic krill, and seeding spring phytoplankton blooms." They state, however, that "brine channel and surface communities have only limited access to the underlying water column and consequently their CO2 supply becomes severely restricted," such that "under these circumstances, restricted CO2 supply limits microalgae growth (McMinn et al., 1999)," so that "unlike planktonic ecosystems where CO2 is rarely in short supply, in sea ice brine systems the shortage is often acute." And, therefore, they opine that "the addition of CO2 as a result of ocean acidification may partially alleviate this stress."

What was done
To assess the likelihood of this possibility, McMinn et al. incubated brine algae - dominated by the unique ice dinoflagellate Polarella glacialis that they had collected from McMurdo Sound (Antarctica) sea ice - under various carbonate chemistry conditions which they manipulated to produce pCO2 and pH ranges stretching from 238 to 6066 ľatm and 7.19 to 8.66, respectively.

What was learned
Brief and to the point, the four researchers from "down under" report that "elevated pCO2 positively affected the growth rate of the brine algal community."

What it means
In the words of McMinn et al., "projected increases in seawater pCO2 associated with ocean acidification, will not adversely impact brine algal communities." In fact, they suggest that such communities may actually "benefit from the associated increases in CO2" that "are likely to be experienced by the end of the century."

Arrigo, K.R. and Thomas, D.N. 2004. Large scale importance of sea ice biology in the Southern Ocean. Antarctic Science 16: 471-486.

McMinn, A., Skerratt, J., Trull, T., Ashworth, C. and Lizotte, M. 1999. Nutrient stress gradient in the bottom 5 cm of fast ice, McMurdo Sound, Antarctica. Polar Biology 21: 220-227.

Reviewed 23 April 2014