How does rising atmospheric CO2 affect marine organisms?

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Early Life Stages of Shrimp and Mussels in Low pH Seawater
Bechmann, R.K., Taban, I.C., Westerlund, S., Godal, B.F., Arnberg, M., Vingen, S., Ingvarsdottir, A. and Baussant, T. 2011. Effects of ocean acidification on early life stages of Shrimp (Pandalus borealis) and mussel (Mytilus edulis). Journal of Toxicology and Environmental Health, Part A 74: 424-438.

What was done
Noting that "there is a particular need to study effects of OA [ocean acidification] on organisms living in cold-water environments due to the higher solubility of CO2 at lower temperatures," the authors maintained mussel (Mytilus edulis) and shrimp (Pandalus borealis) larvae under the OA scenario predicted for the year 2100 (pH 7.6) and compared them against batches of larvae held under the current oceanic pH of 8.1 (the control treatment), while water temperature was kept at a constant 10°C in the mussel experiment and 5°C in the shrimp experiment.

What was learned
Bechmann et al. report that, on the positive side, "there was no marked effect on fertilization success, development time, or abnormality to the D-shell stage, or on feeding of mussel larvae in the low-pH treatment," and they say that the M. edulis larvae "were still able to develop a shell in seawater under-saturated with respect to aragonite (a mineral form of CaCO3)." On the negative side, they found that after two months of exposure, the mussels were 28% smaller in the pH 7.6 treatment than in the control treatment. However, they say that "if only the larger larvae settle and survive in the field, the effects of OA on the mussel population may not be dramatic."

In the case of the shrimp study, which ran from day 1 through day 36 post-hatching, they report that survival of the larvae was not reduced at any time during the experiment, but that there was "a significant delay in zoeal progression (development time)," which "may increase the chance of loss by predation." However, they note that "a multi-generation experiment with the copepod Acartia tonsa showed that effects of OA observed in the first generation were no longer present in the second and third generation (Dupont and Thorndyke, 2009)," implying that such could also prove to be the case in the situation they were investigating.

What it means
In light of these several short-term findings and lack of long-term findings, the eight Norwegian researchers conclude their paper by saying "there are different opinions about how to extrapolate the effects of OA from a single species examined in relatively short-term experiments to the population and ecosystem level," while noting that "all agree that more data from relevant long-term experiments are needed to better predict effects at higher levels of biological organization," citing the work of Dupont et al. (2010a,b), Hendriks and Duarte (2010), Hendricks et al. (2010) and Widdicombe and Spicer (2008). So here's hoping more long-term OA studies -- similar to the multi-year free-air CO2-enrichment or FACE studies that have been conducted on trees -- will soon be initiated on various marine organisms.

Dupont, S. and Thorndyke, M.C. 2009. Impact of CO2-driven ocean acidification on invertebrates early life-history -- What we know, what we need to know, and what we can do. Biogeoscience Discussions 6: 3109-3131.

Dupont, S., Dorey, N. and Thorndyke, M. 2010a. What meta-analysis can tell us about vulnerability of marine biodiversity to ocean acidification? Estuarine, Coastal and Shelf Science 89: 182-185.

Dupont, S., Ortega-Martinez, O. and Thorndyke, M. 2010b. Impact of near-future ocean acidification on echinoderms. Ecotoxicology 19: 449-462.

Hendriks, I.E. and Duarte, C.M. 2010. Ocean acidification: Separating evidence from judgment -- A reply to Dupont et al. Discussion. Estuarine, Coastal and Shelf Science 86: 186-190.

Hendriks, I.E., Duarte, C.M. and Alvarez, M. 2010. Vulnerability of marine biodiversity to ocean acidification: A meta-analysis. Estuarine, Coastal and Shelf Science 86: 157-164.

Reviewed 27 July 2011