Background
The authors write that "copepods (Crustacea; Copepoda) are considered to constitute the most numerous multicellular organisms on earth (Mauchline, 1998)," and they say that they thus "play a vital role in marine food webs," while noting that "the copepod investigated in the present study, Calanus finmarchicus, seasonally dominates the zooplankton biomass in the surface waters of the northern North Sea and the North Atlantic," citing Conover (1988) and Planque and Batten (2000) in this regard.

What was done
As described by Pedersen et al., "the impact of medium-term exposure to CO2 acidified seawater on survival, growth and development was investigated in the North Atlantic copepod Calanus finmarchicus," where using a custom-developed experimental system, "fertilized eggs and subsequent development stages were exposed to normal seawater (390 ppm CO2) or one of three different levels of CO2-induced acidification (3300, 7300, 9700 ppm CO2)."

What was learned
The four Norwegian researchers report that (1) "following the 28-day exposure period, survival was found to be unaffected by exposure to 3300 ppm CO2, but significantly reduced at 7300 and 9700 ppm CO2," that (2) "the proportion of copepodite stages IV to VI observed in the different treatments was significantly affected in a manner that may indicate a CO2-induced retardation of the rate of ontogenetic development," and that (3) "morphometric analysis revealed a significant increase in size (prosome length) and lipid storage volume in stage IV copepodites exposed to 7300 ppm CO2."

What it means
In light of these several findings, Pedersen et al. write, in the concluding paragraph of their paper, that "the absence of any apparent reduction in the overall survival during the present medium-term exposure to 3300 ppm CO2, indicates that survival of Calanus eggs and nauplii may be robust against the direct effects of the worst-case CO2 scenario predicted for year 2300."

References
Conover, R.J. 1988. Comparative life histories in the genera Calanus and Neocalanus in high latitudes of the northern hemisphere. Hydrobiologia 167/168: 127-142.

Mauchline, J. 1998. The biology of calanoid copepods. In: Blaxter, J.H.S., Southward, A.J. and Tyler, P.A. (Eds.). Advances in Marine Biology. Academic Press, London, United Kingdom.

Planque, B. and Batten, S.D. 2000. Calanus finmarchicus in the North Atlantic; the year of Calanus in the context of interdecadal changes. ICES Journal of Marine Science 57: 1528-1535.