Background
The authors write that "since the recruitment of fish seems to be determined during the early life stages (Koester et al., 2003; Houde, 2008), knowledge of the factors influencing growth and survival rates of these stages are of great importance in fisheries science." And they add, in this regard, that "early life history stages even of the more tolerant taxa are assumed to be most susceptible to ocean acidification (Raven et al., 2005; Melzner et al., 2009)." But is this latter assumption correct?

What was done
Seeking to answer this question for the case of the Atlantic herring (Clupea harengus L.), Franke and Clemmesen conducted a study in which eggs of the fish were fertilized and incubated in artificially acidified seawater corresponding to atmospheric CO2 concentrations of 1260, 1859, 2626, 2903 and 4635 ppm and compared to a control treatment of 480 ppm CO2 until the main hatch of the herring larvae occurred, after which they say that "the development of the embryos was monitored daily and newly hatched larvae were sampled to analyze their morphometrics."

What was learned
The two researchers from the Leibniz-Institute of Marine Sciences at Kiel (Germany) report that elevated CO2 "neither affected the embryogenesis nor the hatch rate," and they say "the results showed no linear relationship between CO2 and total length, dry weight, yolk sac area and otolith area of the newly hatched larvae."

What it means
Franke and Clemmesen conclude that "herring eggs can cope at current temperature conditions with an increase in CO2," even one "exceeding future predictions of CO2-driven ocean acidification."

References
Houde, E.D. 2008. Emerging from Hjort's Shadow. Journal of Northwest Atlantic Fishery Science 41: 53-70.

Koester, F.W., Hinrichsen, H.H., Schnack, D., St. John, M.A., Mackienzie, B.R., Tomkiewicz, J., Mollmann, C., Kraus, G., Plikshs, M., Makarchouk, A. and Aro, E. 2003. Recruitment of Baltic cod and sprat stocks: identification of critical life stages and incorporation of environmental variability into stock-recruitment relationships. Scientia Marina 67: 129-154.

Melzner, F., Gutowska, M.A., Langenbuch, M., Dupont, S., Lucassen, M., Thorndyke, M.C., Bleich, M. and Portner, H.O. 2009. Physiological basis for high CO2 tolerance in marine ectothermic animals: pre-adaptation through lifestyle and ontogeny? Biogeosciences 6: 213-2331.

Raven, J., Caldeira, K., Elderfield, H., Hoegh-Guldberg, O., Liss, P.S., Riebesell, U., Shepherd, J., Turley, C. and Watson, A.J. 2005. Ocean Acidification Due to Increasing Atmospheric Carbon Dioxide. Policy Document 12/05, The Royal Society, London, United Kingdom.