How does rising atmospheric CO2 affect marine organisms?

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Aquatic Ecosystems of Arid and Semi-Arid Regions
Morrongiello, J.R., Crook, D.A., King, A.J., Ramsey, D.S. and Brown, P. 2011. Impacts of drought and predicted effects of climate change on fish growth in temperate Australian lakes. Global Change Biology 17: 745-755.

The authors write that "according to a range of modeled scenarios, many arid and semiarid regions across the world are likely to become warmer and drier over the next century due to human-induced climate change," citing the IPCC (2007) and Bates et al. (2008). And they note, in this regard, that the information reported in the review of Lake (2003) suggests that "more frequent and longer duration droughts will potentially have detrimental impacts on aquatic species."

What was done
Noting that such warmer and drier conditions "can already be found today in areas experiencing significant drought," the five researchers analyzed the width of the yearly growth increments laid down in the otoliths (earstones) of populations of a native fish species (the golden perch) living in two artificial impoundments (Lakes Mokoan and Eppalock) near their southerly distribution limits in central Victoria, Australia, over a 15-year period that both pre-dated and encompassed a significant supra-seasonal drought.

What was learned
Morrongiello et al. determined that "fish growth declined as water levels in the lakes dropped during the drought," but they say that "this effect was offset by increased growth in warmer years." In fact, it was more than offset; because based on the relationships they developed from their real-world data, they found that the 2070 mean annual growth of two-year-old golden perch in Lakes Mokoan and Eppalock, respectively, was estimated to increase by 14.9% and 17.2% under low CO2 emission and 56.5% and 58.6% under high CO2 emission scenarios compared with 1990 CO2 levels.

What it means
In discussing their findings, the Australian scientists conclude that "despite climatic models predicting significant declines in future water availability, fish growth may increase due to a disproportionate lengthening of the growing season." Thus, they predict that "golden perch growth rates in southerly [Australian] populations may increase as warmer conditions associated with climate change will lengthen the growing season and make these high [southern] latitude habitats more favorable."

Bates, B.C., Kundzewicz, Z.W., Wu, S. and Palutikof, J.P. (Eds.) 2008. Climate Change and Water. Technical Paper of the Intergovernmental Panel on Climate Change. IPCC Secretariat, Geneva, Switzerland.

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.

Lake, P.S. 2003. Ecological effects of perturbation by drought in flowing waters. Freshwater Biology 48: 1161-1172.

Reviewed 8 June 2011