How does rising atmospheric CO2 affect marine organisms?

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Long-Term Responses of Emiliania huxleyi to Ocean Acidification
Benner, I., Diner, R.E., Lefebvre, S.C., Li, D., Komada, T., Carpenter, E.J. and Stillman, J.H. 2014. Emiliania huxleyi increases calcification but not expression of calcification-related genes in long-term exposure to elevated temperature and pCO2. Philosophical Transactions of the Royal Society B 368: 10.1098/rstb.2013.0049.

In introducing their recent study, the authors write that "earlier studies tested the response of E. huxleyi to elevated pCO2 in short-term experiments (less than 20 generations)," and they go on to say that "this is potentially problematic, because organisms with short generation times and large population size, such as E. huxleyi, have high potential for acclimation and adaptation to natural environmental change (Elena and Lenski, 2003; Tatters et al., 2013)," adding that "adaptation to future ocean conditions might change calcification responses compared with short-term acclimation."

What was done
"To explore the long-term effect of future ocean conditions on E. huxleyi," in the words of Benner et al., they "grew strain CCMP 371 in continuous culture under simultaneously elevated pCO2 and temperature: 'present' ocean conditions (383 ± 43 µatm pCO2 and 20.0 ± 0.1°C average across all generation points) and 'future' ocean conditions (833 ± 68 µatm pCO2 and 24.0 ± 0.2°C average across all generation points."

What was learned
The seven scientists report that (1) "genome-wide profiles of gene expression using RNA-seq revealed that genes thought to be essential for calcification are not those that are most strongly differentially expressed under long-term exposure to future ocean conditions," and it was consequently not too surprising that they found that (2) "cells increased inorganic carbon content and calcification rate under warm and acidified conditions compared with ambient conditions."

What it means
Once again quoting the researchers who did the work, they say that "in contrast to findings from short-term experiments, our results suggest that long-term acclimation or adaptation could change, or even reverse, negative calcification responses in E. huxleyi and its feedback to the global carbon cycle," which change would tend to temper the rate of rise of the atmosphere's CO2 concentration.

Elena, S.F. and Lenski, R.E. 2003. Evolution experiments with microorganisms: the dynamics and genetic bases of adaptation. Nature Reviews Genetics 4: 457-469.

Tatters , A.O., Roleda, M.Y., Schnetzer, A., Fu, F., Hurd, C.L., Boyd, P.W., Caron, D.A., Lie, A.A.Y., Hoffmann, L.J. and Hutchins, D.A. 2013. Short- and long-term conditioning of a temperate marine diatom community to acidification and warming. Philosophical Transactions of the Royal Society B 368: 10.1098/rstb.2012.0437.

Reviewed 23 April 2014