How does rising atmospheric CO2 affect marine organisms?

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Responses of Juvenile Mussels to Experimentally Acidified Seawater
Fernandez-Reiriz, M.J., Range, P., Alvarez-Saldago, X.A., Espinosa, J. and Labarta, U. 2012. Tolerance of juvenile Mytilus galloprovincialis to experimental seawater acidification. Marine Ecology Progress Series 454: 65-74.

The authors write that "coastal ocean acidification is expected to interfere with the physiology of marine bivalves." In fact, they state that CO2-induced changes in pH are expected by some scientists to negatively affect the physiology of all marine life. But since bivalves dominate the macrofauna of many estuaries and coastal embayments, they decided to target the mussel Mytilus galloprovincialis for further study, since it is a species that is distributed worldwide and that dominates the extensive cultures of the Galician rias (bays and inlets) of northwest Spain.

What was done
Working with juvenile M. galloprovincialis specimens that were obtained from a mussel raft in the Ria de Ares-Betanzos, and that were reared in an experimental bivalve hatchery in Tavira, Portugal, Fernandez-Reiriz et al. tested the effects of three levels of seawater acidification caused by increasing concentrations of atmospheric CO2: a natural control level plus two lesser levels of pH, one reduced by 0.3 pH unit and another reduced by 0.6 pH unit. This they did by measuring several responses of the mussels after 78 days of exposure to the three sets of pH conditions, focusing on clearance and ingestion rate, absorption efficiency, oxygen consumption, ammonia excretion, oxygen to nitrogen ratio, and scope for growth.

What was learned
The five researchers report that significant differences among treatments were not observed for clearance, ingestion and respiration rates. However, they say that the absorption efficiency and ammonium excretion rate of the juvenile mussels were inversely related to the 0.6 pH reduction, while the maximal scope for growth and tissue dry weight were also observed in the mussels exposed to the pH reduction of 0.6 unit.

What it means
Fernandez-Reiriz et al. conclude their report by stating that their results suggest that Mytilus galloprovincialis "could be a tolerant ecophysiotype to CO2 acidification, at least in highly alkaline coastal waters," while noting that "mytilids are also able to dominate habitats with low alkalinity and high pCO2," citing the work of Thomsen et al. (2010) in this regard. And so it would indeed appear that juvenile mussels may well be able to survive - and possibly even thrive - in a CO2-enriched world of the future.

Thomsen, J., Gutowska, M.A., 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 Discussions 7: 5119-5156.

Reviewed 9 January 2013