How does rising atmospheric CO2 affect marine organisms?

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Adaptive Evolution in the Sea's Most Abundant Primary Producer
Volume 16, Number 18: 1 May 2013

In a paper published in Nature Geoscience back in May of 2012, Lohbeck et al. wrote that "our present understanding of the sensitivity of marine life to ocean acidification is based primarily on short-term experiments, in which organisms are exposed to increased concentrations of CO2," which protocol of expediency leaves no time to observe what could happen in the real world of nature, where given sufficient time evolutionary forces may play a crucial role in determining whether or not the species involved could survive the environmental change expected to result from projected increases in anthropogenic CO2 emissions. So what's the real story here?

The four German researchers began their analysis of the situation by noting that phytoplankton species with short generation times "may be able to respond to environmental alterations through adaptive evolution." And, therefore, they examined the ability of the world's most important calcifying organism, the coccolithophore Emiliania huxleyi, to evolve in response to ocean acidification in two 500-generation selection experiments, where they "exposed E. huxleyi populations founded by single or multiple clones to increased concentrations of CO2," and where 500 generations later they assessed their fitness to both photosynthesize and calcify. And what did they learn?

Lohbeck et al. report that "compared with populations kept at ambient CO2 partial pressure, those selected at increased partial pressure exhibited high growth rates, in both the single- and multi-clone experiment, when tested under ocean acidification conditions." And they also found that "calcification was partly restored." More specifically, they say that "rates were lower under increased CO2 conditions in all cultures, but were up to 50% higher in adapted compared with non-adapted cultures." And in light of these observations, they went on to suggest that "contemporary evolution could help to maintain the functionality of microbial processes at the base of marine food webs in the face of global change."

Writing about this development in a News & Views item in the same issue of Nature Geoscience, Collins (2012) also highlighted the fact that "marine microbes, with their large population sizes and fast division rates, are certainly going to evolve over a timeframe of decades," and that "we can expect that future cocolithophore populations will be shaped by a combination of species succession and adaptive evolution," both of which phenomena bode well, indeed, for the future of earth's marine biosphere.

Sherwood, Keith and Craig Idso

Collins, S. 2012. Evolution on acid. Nature Geoscience 5: 310-311.

Lohbeck, K.T., Riebesell, U. and Reusch, T.B.H. 2012. Adaptive evolution of a key phytoplankton species to ocean acidification. Nature Geoscience 5: 346-351.