How does rising atmospheric CO2 affect marine organisms?

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N Fixation and Growth of Cyanobacteria in CO2-Enriched Sea Water

Paper Reviewed
Hutchins, D.A., Walworth, N.G., Webb, E.A., Saito, M.A., Moran, D., Mcllvin, M.R., Gale, J. and Fu, F.-X. 2015. Irreversibly increased nitrogen fixation in Trichodesmium experimentally adapted to elevated carbon dioxide. Nature Communications: 10.1038/ncomms9155.

Atmospheric nitrogen (N2) fixation by marine cyanobacteria -- also known as blue-green algae -- is a globally-dominant source of this important nutrient for the world's oceanic biosphere (Zehr, 2011); and it is also known that the colony-forming Trichodesmium genus may produce as much as one half of the total N2 fixed in the world's tropical oceans (Sohm et al., 2011). Consequently, in the intriguing study here reviewed, Hutchins et al. (2015) grew six replicate cell lines of the Trichodesmium erythraeum strain IMS 101 for four and a half years in special bottles through which air containing either 380 ppm CO2 (for about 570 generations) or 750 ppm CO2 (for about 850 generations), after which they evaluated changes in their reproductive fitness using growth rate measurements, as well as changes in their physiological rates of N2 fixation.

This work revealed, in the words of the eight U.S. scientists, that "experimental evolution under extended selection at projected future elevated CO2 levels results in irreversible, large increases in nitrogen fixation and growth rates, even after being moved back to lower present-day CO2 levels for hundreds of generations."

In light of these amazing findings, Hutchins et al. go on to state that their results represent "an unprecedented microbial evolutionary response, as reproductive fitness increases acquired in the selection environment are maintained after returning to the ancestral environment." And they further add that the "high CO2-selected cell lines also exhibit increased phosphorus-limited growth rates, suggesting a potential advantage for this keystone organism in a more nutrient-limited, acidified future ocean."


Sohm, J.A., Webb, E.A. and Capone, D.G. 2011. Emerging patterns of marine nitrogen fixation. Nature Reviews Microbiology 9: 499-508.

Zehr, J.P. 2011. Nitrogen fixation by marine cyanobacteria. Trends in Microbiology 19: 162-173.

Posted 16 February 2016