Background
The authors write that future scenarios of ocean acidification or OA "do not reflect patterns described for most coastal areas (Wootton et al., 2008; Feely et al., 2010; Melzner et al., 2013)," noting that "in coastal regions, river runoff, upwelling, eutrophication and biological activity modify the effects of atmospherically driven OA (Duarte et al., 2013)." And they say that "in highly productive areas, this leads to severe fluctuations in the carbonate system at frequencies from hours to months and produces local levels of acidification that can greatly exceed average projections for the end of this century," citing Caldeira and Wickett (2003), Wootton et al. (2008), Miller et al. (2009), Feely et al. (2010) and Duarte et al. (2013).

In the Western Baltic Sea's Kiel Fjord, for example, Pansch et al. report that "annual mean surface seawater pCO2 is typically ca. 800 µatm, and peak values of 2400 µatm occur during upwelling events," citing Thomsen et al. (2010, 2013), Melzner et al. (2013) and Saderne et al. (2013). And these huge OA values led them to wonder how marine invertebrates ever survived there.

What was done
In a long-term study designed to explore this situation, the four scientists say they investigated the effects of food availability and elevated pCO2 (ca. 400, 1000 and 3000 µatm) on the growth of newly settled barnacles (Amphibalanus improvisus) all the way to reproduction, and on their offspring, which they did for "two different populations, which were presumed to differ in their sensitivity to pCO2 due to differing habitat conditions" - Kiel Fjord, as noted above, and the Tjarno Archipelago, Sweden (Skagerrak), which has far lower fluctuations in seawater pH.

What was learned
Pansch et al. report that over a period of 20 weeks, the survival, growth, reproduction and shell strength of Kiel barnacles "were all unaffected by pCO2, regardless of food availability," and that "larval development and juvenile growth of the F1 generation were tolerant to increased pCO2, irrespective of parental treatment." In contrast, they report that "elevated pCO2 had a strong negative impact on survival of Tjarno barnacles," with specimens from this population being "able to withstand moderate levels of elevated pCO2 over five weeks when food was plentiful," but which "showed reduced growth under food limitation." In addition, they found that "severe levels of elevated pCO2 negatively impacted the growth of Tjarno barnacles in both food treatments."

What it means
In discussing their findings, Pansch et al. say they indicate that "populations from fluctuating pCO2 environments are more tolerant to elevated pCO2 than populations from more stable pCO2 habitats." And so they conclude that "considering the high tolerance of Kiel specimens and the possibility to adapt over many generations, near future OA alone does not seem to present a major threat for A. improvisus."

References
Caldeira, K. and Wickett, M.E. 2003. Anthropogenic carbon and ocean pH. Nature 425: 365.

Duarte, C.M., Hendriks, I.E., Moore, T.S., Olsen, Y.S., Steckbauer, A., Ramajo, L., Carstensen, J., Trotter, J.A. and Mcculloch, M. 2013. Is ocean acidification an open-ocean syndrome? Understanding anthropogenic impacts on seawater pH. Estuaries and Coasts 36: 221-236.

Feely, R.A., Alin, S.R., Newton, J., Sabine, C.L., Warner, M., Devol, A., Krembs, C. and Maloy, C. 2010. The combined effects of ocean acidification, mixing, and respiration on pH and carbonate saturation in an urbanized estuary. Estuarine, Coastal and Shelf Science 88: 442-449.

Melzner, F., Thomsen, J., Koeve, W. Oschlies, A., Gutowska, M.A. and Bange, H.W. 2013. Future ocean acidification will be amplified by hypoxia in coastal habitats. Marine Biology 8: 1875-1888.

Miller, A.W., Reynolds, A.C., Sobrino, C. and Riedel, G.F. 2009. Shellfish face uncertain future in high CO2 world: influence of acidification on oyster larvae calcification and growth in estuaries. PLOS ONE 4: e5661.

Saderne, V., Fietzek, P. and Herman, P.M.J. 2013. Extreme variations of pCO2 and pH in a macrophyte meadow of the Baltic Sea in summer: evidence of the effect of photosynthesis and local upwelling. PLOS ONE 8: e62689.

Thomsen, J., Gutowska, M., Saphorster, J. A. Heinemann, A., Trübenbach, K., Fietzke, J., Hiebenthal, C., Eisenhauer, A., Körtzinger, A., Wahl, M. and Melzner, F. 2010. Calcifying invertebrates succeed in a naturally CO2-rich coastal habitat but are threatened by high levels of future acidification. Biogeosciences 7: 3879-3891.

Thomsen, J., Casties, J., Pansch, C., Kortzinger, A. and Melzner, F. 2013. Food availability outweighs ocean acidification effects in juvenile Mytilus edulis: laboratory and field experiments. Global Change Biology 19: 1017-1027.

Wootton, J.T., Pfister, C.A. and Forester, J.D. 2008. Dynamic patterns and ecological impacts of declining ocean pH in a high-resolution multi-year dataset. Proceedings of the National Academy of Sciences USA 105: 18,848-18,853.