How does rising atmospheric CO2 affect marine organisms?

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Effects of Elevated CO2 on the Growth of Marine Algae
Moazami-Goudarzi, M. and Colman, B. 2012. Changes in carbon uptake mechanisms in two green marine algae by reduced seawater pH. Journal of Experimental Marine Biology and Ecology 413: 94-99.

From pre-industrial times to the present, the atmosphere's CO2 concentration has risen well in excess of 100 ppm, leading to a drop of 0.1 pH unit in earth's seawater, while anticipated CO2 increases to the end of the current century are suggestive of a further drop of 0.3-0.5 pH unit, according to Caldeira and Wickett (2003, 2005). So what do these projections portend for the productivity of the world's marine algae?

What was done
In a study of two such green marine algae (Stichococcus cylindricus and Stichococcus minor), Moazami-Goudarzi and Colman measured their growth rates while growing them in artificial seawater - as per Berges et al. (2001) - within 125-ml Erlenmeyer flasks at pH values of 5.0, 6.0, 7.0, 8.2, 9.0 and 9.5, as well as at a variety of salinity levels (25, 50, 100, 200 and 470 mM).

What was learned
The two Canadian researchers report that "both species were found to have similar growth rates and grew over the range of pH 5.0 to 9.5 with optimal rates at pH 8.2," with cells grown at pH 5.0, 6.0 and 7.0 showing no significant difference in growth rates. Likewise, they similarly report that "both species were found to have similar growth rates and to grow over a range of salinities at sodium chloride concentrations of 25, 50, 100, 200 and 470 mM."

What it means
With Moazami-Goudarzi and Colman determining that S. minor and S. cylindricus "were able to tolerate a broad range of pH from pH 5.0 to 9.5," as well as the broad range of salinities they investigated, it would appear that even the worst nightmare of the world's climate alarmists would not be a great impediment to the continued wellbeing of these two green marine algae, even without the positive influence of evolutionary forces that would likely come into play over the timespan involved in the seawater transformations envisioned by Caldeira and Wickett. See Evolution in our Subject Index.

Berges, J.A., Franklin, D.J. and Harrison, P.J. 2001. Evolution of an artificial seawater medium: improvements in enriched seawater, artificial water over the last two decades. Journal of Phycology 37: 1138-1145.

Caldeira, K. and Wickett, M.E. 2003. Anthropogenic carbon and ocean pH. Nature 425: 365.

Caldeira, K. and Wickett, M.E. 2005. Ocean model predictions of chemistry changes from carbon dioxide emissions to the atmosphere and ocean. Journal of Geophysical Research 110: 10.1029/2004JC002671.

Reviewed 27 June 2012