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An Arctic Copepod is Unaffected by Ocean Acidification

Paper Reviewed
Bailey, A., Thor, P., Browman, H.I., Fields, D.M., Runge, J., Vermont, A., Bjelland, R., Thompson, C., Shema, S., Durif, C.M.F. and Hop, H. 2017. Early life stages of the Arctic copepod Calanus glacialis are unaffected by increased seawater pCO2. ICES Journal of Marine Science 74: 996-1004.

Writing as background for their study, Bailey et al. (2017) note that the Arctic seas "are expected to experience the largest pH decrease in the future because cold, low-salinity waters have greater uptake of CO2, lower buffering capacity, and thus larger decreases in pH for a given pCO2 than lower latitude seas." It is therefore anticipated that the impacts of future ocean acidification will be among the most severe in these waters than perhaps any other location.

Against this backdrop of concern this team of eleven researchers set out to investigate the impacts of increased pCO2 on a key Arctic copepod, Calanus glacialis. C. glacialis constitutes up to 90% of zooplankton biomass in the shelf regions of the Arctic and it is an important source of food to predators in the Arctic marine ecosystem. Therefore, Bailey et al. felt it important to study the response of this species to predictions of future pH decline.

To accomplish their objective, the researchers exposed wild-caught C. glacialis eggs to four pH/pCO2 levels (pH 8.05/320 µatm, pH 7.90/530 µatm, pH 7.70/800 µatm and pH 7.50/1700 µatm) for a period of two months, measuring and tracking their development through the six naupliar stages of development. It was their hypothesis that low seawater pH would "impose and energetic cost on developing C. glacialis, resulting in slowed development, reduced growth, and increased respiration."

In describing their findings, Bailey et al. report that "the early life stages (N1-N6) of C. glacialis were unaffected by increased pCO2 levels predicted for the year 2300: naupliar developmental rate, growth (dry weight, carbon body mass, C:N ratio), and metabolic rate were indistinguishable over the range of 320-1700 µatm pCO2." Such results, in the words of the authors, "do not support our original hypothesis of increased energetic costs of pCO2 during early development" and "indicate that C. glacialis will maintain normal development, growth, and metabolic rate in a high pCO2 ocean."

With respect to why this positive outcome is the case, Bailey et al. say it is likely due to the natural variability experienced by C. glacialis in its environment, writing that "organisms inhabiting coastal areas, where pH varies on diurnal and seasonal scales, or those migrating horizontally and/or vertically through water masses of variable pH, may be adapted to perform well over a range of pHs." Thus, they conclude that "C. glacialis may already be adapted to tolerate variable pH and pCO2 due to the seasonal and spatial variability of its natural Arctic habitat."

Posted 26 July 2017