How does rising atmospheric CO2 affect marine organisms?

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Marine Coccolithophore Photosynthesis in a CO2-Enriched Warmer World
Feng, Y., Warner, M.E., Zhang, Y., Sun, J., Fu, F.-X., Rose, J.M. and Hutchins, A. 2008. Interactive effects of increased pCO2, temperature and irradiance on the marine coccolithophore Emiliania huxleyi (Prymnesiophyceae). European Journal of Phycology 43: 87-98.

What was done
The authors grew the marine coccolithophore Emiliania huxleyi, which they isolated from the Sargasso Sea, by semi-continuous culture methods at two different (low, high) light intensities (50 and 400 Ámol photons/m2/sec), two different (low, high) temperatures (20 and 24░C), and two different (low, high) CO2 concentrations (375 and 750 ppm).

What was learned
Feng et al. report that in the low-light environment, the chlorophyll a-normalized photosynthetic rates of the coccolithophores in all four temperature/CO2 treatments attained maximum values at an irradiance of approximately 200 Ámol photons/m2/sec, where the maximum rate was lowest in the low-temperature, low-CO2 or ambient treatment, but was significantly increased by 55% by elevated temperature alone and by 95% by elevated CO2 alone, while in the high-temperature, high-CO2 or greenhouse treatment it was increased by 150% relative to the ambient treatment. In the high-light environment, on the other hand, the chlorophyll a-normalized photosynthetic rates did not max out below the maximum irradiance tested (900 Ámol photons/m2/sec) for any but the ambient treatment. Hence, the equations fit to the data of the other treatments were extrapolated to their respective photosynthetic maxima, which produced corresponding maximum photosynthetic rate increases of 58%, 67% and 92% for the elevated temperature alone, elevated CO2 alone and greenhouse treatments, respectively. Last of all, in the high-light greenhouse treatment characteristic of the future, the maximum photosynthetic rate was found to be 178% greater than what it was in the low-light ambient treatment characteristic of the present.

What it means
In the words of the seven researchers, "these results suggest that future trends of CO2 enrichment, sea-surface warming and exposure to higher mean irradiances from intensified [surface water] stratification will have a large influence on the growth of Emiliania huxleyi." And, of course, that "large influence" will be positive.

Reviewed 25 June 2008