How does rising atmospheric CO2 affect marine organisms?

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Juvenile Barnacles in a Significantly Warmed and Acidified Ocean
Pansch, C., Nasrolahi, A., Appelhans, Y.S. and Wahl, M. 2013. Tolerance of juvenile barnacles (Amphibalanus improvisus) to warming and elevated pCO2. Marine Biology 160: 2023-2035.

The authors say that Kiel Fjord in the western Baltic Sea "is characterized by strong fluctuations in water pCO2 and pH," and that annual mean pCO2 values of about 700 ľatm can be measured there today, "with occasional pCO2 peaks of up to ~2,300 ľatm (Thomsen et al., 2010)." And they therefore wondered how juvenile barnacles (Amphibalanus improvisus) would fare there in the future, as the air's CO2 content continues to rise and if temperatures rise along with it.

What was done
A. improvisus juveniles were collected by exposing transparent settlement panels to the subtidal zone of the inner Kiel Fjord for two weeks, after which the panels with the juvenile barnacles were distributed to the different treatment combinations Pansch et al. created in the laboratory: seawater of two temperatures (20 and 24°C) and three ocean acidification levels (mean pCO2 values of 700, 1000 and 2140 ľatm). There they were fed a mix of two marine diatoms every other day until day 24, after which they were additionally fed with specified amounts of brine shrimp until the end of the experiment on day 62.

What was learned
In the words of the four German scientists, they observed "reduced growth rates as well as weakening of barnacle shells only under very high pCO2 (>1930 ľatm)." However, they add that "even under these highly acidified conditions, and corroborating other recent investigations on barnacles (e.g., McDonald et al., 2009; Findlay et al., 2010a,b), these impacts were subtle and sub-lethal." And "furthermore," as they continue, "ocean warming as expected to occur in the future (IPCC, 2007) has the potential to mitigate the negative effects of ocean acidification (Brennand et al., 2010; Waldbusser, 2011; present study)."

What it means
In light of the findings of Pansch et al., as well as those of the other researchers they cite, it would appear that juvenile barnacles of the species they studied are already well equipped to meet the challenges of a significantly warmed and acidified ocean.

Brennand, H.S., Soars, N., Dworjanyn, S.A., Davis, A.R. and Byrne, M. 2010. Impact of ocean warming and ocean acidification on larval development and calcification in the sea urchin Tripneustes gratilla. PLoS ONE 5: 10.1371/journal.pone.0011372.

Findlay, H.S., Burrows, M.T., Kendall, M.A., Spicer, J.I. and Widdicombe, S. 2010a. Can ocean acidification affect population dynamics of the barnacle Semibalanus balanoides at its southern range edge? Ecology 91: 2931-2940.

Findlay, H.S., Kendall, M.A., Spicer, J.I. and Widdicombe, S. 2010b. Relative influences of ocean acidification and temperature on intertidal barnacle post-larvae at the northern edge of their geographic distribution. Estuarine, Coastal and Shelf Science 86: 675-682.

IPCC. 2007. Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge University Press, Cambridge, United Kingdom.

McDonald, M.R., McClintock, J.B., Amsler, C.D., Rittschof, D., Angus, R.A., Orihuela, B. and Lutostanski, K. 2009. Effect of ocean acidification over the life history of the barnacle Amphibalanus amphitrite. Marine Ecology Progress Series 385: 179-187.

Thomsen, J., Gutowska, M., Saphorster, J., Heinemann, A., Trubenbach, K., Fietzke, J., Hiebenthal, C., Eisenhauer, A., Kortzinger, 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.

Waldbusser, G.G. 2011. The causes of acidification in Chesapeake Bay and consequences to oyster shell growth and dissolution. Journal of Shellfish Research 30: 559-560.

Reviewed 18 December 2013