How does rising atmospheric CO2 affect marine organisms?

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Calcifying Marine Invertebrates "Living in the Future"
Volume 14, Number 18: 4 May 2011

Many are the doom-and-gloom prognostications for earth's calcifying marine invertebrates -- based on what Thomsen et al. (2010) describe as "short to intermediate (days to weeks) CO2 perturbation experiments" -- if the air's CO2 content continues to rise and the pH values of the world's ocean waters concomitantly decline, in a phenomenon that has come to be known by the fright-inducing moniker of ocean acidification. However, the eleven German researchers note that "as most laboratory experiments cannot account for species genetic adaptation potential, they are limited in their predictive power," and that "naturally CO2-enriched habitats have thus recently gained attention, as they could more accurately serve as analogues for future, more acidic ecosystems."

Taking this latter course, Thomsen et al. studied the macrobenthic community in Kiel Fjord -- a naturally-CO2-enriched site in the Western Baltic Sea -- that is dominated by calcifying marine invertebrates, where they determined that in 34%, 23% and 9% of the 42 weeks they were there, the partial pressure (p) of CO2 in the water exceeded pre-industrial pCO2 (280 ppm) by a factor of three (>840 ppm), four (>1120 ppm) and five (>1400 ppm), respectively. And what did they find under these conditions?

The team of German scientists reports that "the macrobenthic community in Kiel Fjord is dominated by calcifying invertebrates," such as the blue mussel (Mytilus edulis), the barnacle Amphibalanus improvisus and the echinoderm Asterias rubens; and they say that "juvenile mussel recruitment peaks during the summer months, when high water pCO2 values of ~1000 ppm prevail." In addition, they say their short-term laboratory research indicates that "blue mussels from Kiel Fjord can maintain control rates of somatic and shell growth at a pCO2 of 1400 ppm." At 4000 ppm pCO2, however, they say that both shell mass and extension rates were significantly reduced; but they found that "regardless of the decreased rates of shell growth at higher [1400] pCO2, all mussels increased their shell mass at least by 150% during the 8-week trial, even at Ωargcalc) as low as 0.17 (0.28)," where Ω is the calcium carbonate saturate state of either aragonite (arg) or calcite (calc).

In concluding the report of their field and laboratory work, as well as their mini-review of the pertinent scientific literature, Thomsen et al. state that it is likely that "long-term acclimation to elevated pCO2 increases the ability to calcify in Mytilus spp.," citing the studies of Michaelidis et al. (2005) and Ries et al. (2009) in addition to their own. And they say that they could find "no causal relationship between the acid-base status and metabolic depression in this species at levels of ocean acidification that can be expected in the next few hundred years (IPCC, 2007)," after discovering in the waters of Kiel Fjord (and demonstrating in the laboratory) that "communities dominated by calcifying invertebrates can thrive in CO2-enriched coastal areas."

Sherwood, Keith and Craig Idso

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

Michaelidis, B., Ouzounis, C., Paleras, A. and Portner, H.O. 2005. Effects of long-term moderate hypercapnia on acid-base balance and growth rate in marine mussels Mytilus galloprovincialis. Maring Ecology Progress Series 293: 109-118.

Ries, J.B., Cohen, A.L. and McCorkle, D.C. 2009. Marine calcifiers exhibit mixed responses to CO2-induced ocean acidification. Geology 37: 1131-1134.

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 7: 3879-3891.