Long-Term Responses of Coccolithophores to Ocean Acidification
Hannisdal, B., Henderiks, J. and Liow, L.H. 2012. Long-term evolutionary and ecological responses of calcifying phytoplankton to changes in atmospheric CO2. Global Change Biology 18: 3504-3516.
In a study designed to determine how coccolithophores might perform in a CO2-enriched world of the future, Hannisdal et al. looked to the distant past, noting that "the last period of sustained high-CO2 (greenhouse) conditions in Earth history ended ~34 Ma [million years ago]." Thus, they combined a comprehensive 50-5 Ma fossil data set on coccolithophore cell size with what they call "a novel measure of ecological prominence" - i.e., the Summed Common Species Occurrence Rate (SCOR) - which parameter, in their words, "captures changes in the extent to which coccolithophores were common and widespread, based on global occurrences in deep-sea sediments," after which they compared the size and SCOR records to state-of-the-art data on climatic and environmental changes from 50 to 5 Ma.
The three Nordic researchers discovered what they called, "a striking relationship between macroevolutionary changes in the coccolithophores and estimated changes in atmospheric pCO2 over a period of 50 million years, spanning one of Earth's major climatic (greenhouse-icehouse) transitions," wherein "coccolithophores were globally more common and widespread, larger, and more heavily calcified in the pre-34 Ma greenhouse world, and declined in both ecological prominence and body size along with pCO2 during the Oligocene (34-23 Ma)."
Hannisdal et al. say their results suggest that "atmospheric pCO2 exerted an important long-term control on coccolithophores, either directly through its availability for photosynthesis or indirectly via weathering supply of resources for growth and calcification." In either event - or both - it is clear that their findings are, as they put it, "consistent with inferred coccolith mass increase with rising atmospheric pCO2 over the past two centuries (Halloran et al., 2008; Iglesias-Rodriguez et al., 2008)," as well as theoretical life-history modeling, which has been shown by Irie et al. (2010) "to predict an increase in coccolithophore size and calcification as an adaptive evolutionary response to ocean acidification".
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Halloran, P.R., Hall, I.R., Colmenero-Hidalgo, E. and Rickaby, R.E.M. 2008. Evidence for a multi-species coccolith volume change over the past two centuries: understanding a potential ocean acidification response. Biogeosciences 5: 1651-1655.
Iglesias-Rodriguez, M.D., Halloran, P.R., Rickaby, R.E.M., Hall, I.R., Colmenero-Hidalgo, E., Gittins, J.R., Green, D.R.H., Tyrrell, T., Gibbs, S.J., von Dassow, P., Rehm, E., Armbrust, E.V. and Boessenkool, K.P. 2008. Phytoplankton calcification in a high-CO2 world. Science 320: 336-340.
Irie, T., Bessho, K., Findlay, H.S. and Calosi, P. 2010. Increasing costs due to ocean acidification drives phytoplankton to be more heavily calcified: optimal growth strategy of coccolithophores. PLoS ONE 5: 313436.
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