How does rising atmospheric CO2 affect marine organisms?

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Ocean Warming and Acidification Impacts on Western Australian Coral Reefs
Cooper, T.F., O'Leary, R.A. and Lough, J.M. 2012. Growth of Western Australian corals in the Anthropocene. Science 335: 593-596.

What was done
Focusing their attention on coral reefs spanning an 11° latitudinal range in the southeast Indian Ocean, the authors collected 27 long cores from massive Porites coral colonies at six locations covering a north-south distance of about 1000 km off the coast of Western Australia; and from these cores they developed 1900-2010 histories of "annual extension (linear distance between adjacent density minima, cm/year), skeletal density (g/cm3), and calcification rate (the product of skeletal density and annual extension, g/cm2/year)," based on gamma densitometry data.

What was learned
Cooper et al. report that at the Houtman Abrolhos Islands - where a relatively large sea surface temperature (SST) increase had occurred (0.10°C/decade) - calcification rates rose by 23.5%, and that at Coral Bay and Tantabiddi, SST increases of 0.8 and 0.6°C/decade were associated with 8.7 and 4.9% increases in decadal calcification rates, respectively, while smaller and non-significant positive trends in calcification rates were apparent at Clerke and Imperieuse Reefs, where the increase in SST was only 0.2°C/decade.

What it means
In discussing their observations, the three Australian researchers indicate that their latter non-significant findings are consistent with those of Helmle et al. (2011), who they say "found a similar non-correlation for the massive coral Montastraea faveolata in the Florida Keys between 1937 and 1996, when there was no significant SST warming." And they write - with respect to the large increases in calcification rates that they documented at the rapidly warming Houtman Abrolhos Islands - that "Lough and Barnes (2000) documented a similar positive correlation, suggesting that calcification rates may, at least initially, increase with global warming." Thus, they conclude that "the rate of change in the thermal environment of coral reefs is currently the primary driver of change in coral calcification rates," driving them ever higher as temperatures rise ever higher, and that "the large-scale phenomenon of ocean acidification is not currently limiting calcification on coral reefs uniformly at a global scale."

Helmle, K.P., Dodge, R.E., Swart, P.K., Gledhill, D.K. and Eakin, C.M. 2011. Growth rates of Florida corals from 1937 to 1996 and their response to climate change. Nature Communications 2: 10.1038/ncomms1222.

Lough, J.B. and Barnes, D.J. 2000. Environmental controls on growth of the massive coral Porites. Journal of Experimental Marine Biology and Ecology 245: 225-243.

Reviewed 23 May 2012