How does rising atmospheric CO2 affect marine organisms?

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A Coccolithophore's Response to Ocean Acidification

Paper Reviewed
Liu, Y.-W., Eagle, R.A., Aciego, S.M., Gilmore, R.E. and Ries, J.B. 2018. A coastal coccolithophore maintains pH homeostasis and switches carbon sources in response to ocean acidification. Nature Communications 9: 2857, DOI: 10.1038/s41467-018-04463-7.

Although many people believe that ocean acidification will harm or inhibit calcification of marine species, Liu et al. (2018) write that "the response of the most prolific ocean calcifiers, coccolithophores, to this perturbation remains under characterized." Therefore, hoping to provide additional insight on this important topic, this team of five scientists conducted a controlled laboratory experiment to investigate the impact of CO2-induced ocean acidification on a widely distributed coccolithophore species, Ochrosphaera neapolitana.

The range of seawater pCO2 examined to deduce such impacts included values pertaining to glacial (226 µatm), present day (339 µatm) and a predicted future (521 µatm) under ocean acidification. Samples of O. neapolitana were cultured under these three pCO2 conditions at the University of North Carolina, Chapel Hill, from 11 January 2012 to 30 January 2012, where the central objective of the scientists was to study this species' ability to "regulate calcifying fluid pH using boron isotopes and a proxy of calcifying fluid pH."

And what did the study reveal?

According to Liu et al., "boron isotopes within the algae's extracellular calcite plates show that this species maintains a constant pH at the calcification site, regardless of CO2-induced changes in pH of the surrounding seawater." What is more, they report that "carbon and oxygen isotopes in the algae's calcite plates and carbon isotopes in the algae's organic matter suggest that O. neapolitana utilize carbon from a single internal dissolved inorganic (DIC) pool for both calcification and photosynthesis, and that a greater proportion of dissolved CO2 relative to HCO3- enters the internal DIC pool under acidified conditions." Consequently, they conclude that "these two observations may explain how O. neapolitana continues calcifying and photosynthesizing at a constant rate under different atmospheric-pCO2 conditions."

The positive results of this study add to the many encouraging findings published by multiple other researchers on this topic (see the multiple reviews we have posted in our Subject Index under the topic of Ocean Acidification). And given these many positive and encouraging findings, it appears that the widespread negative projections of an ocean acidification-induced disaster are themselves dissolving away.

Posted 14 December 2018