How does rising atmospheric CO2 affect marine organisms?

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The Failing Frogs of Eastern Australia
Laurance, W.F. 2008. Global warming and amphibian extinctions in eastern Australia. Austral Ecology 33: 1-9.

What was done
The author tested the hypothesis -- put forward by Pounds et al. (2006) -- that "the dramatic, fungal pathogen-linked extinctions of numerous harlequin frogs (Atelopus spp.) in upland rainforests of South America mostly occurred immediately following exceptionally warm years, implicating global warming as a likely trigger for these extinctions." This he did "using temperature data for eastern Australia, where at least 14 upland-rainforest frog species have also experienced extinctions or striking population declines attributed to the same fungal pathogen [Batrachochytrium dendrobatidus, a waterborne chytrid-fungus], and where temperatures have also risen significantly in recent decades."

What was learned
Laurance reports that his analyses "provide little direct support for the warm-year hypothesis of Pounds et al." Instead, he says he "found stronger support for a modified version of the warm-year hypothesis," where frog declines were only likely to occur following three consecutive years of unusually warm weather; and he adds that such was observed "only at tropical latitudes, where rising minimum temperatures were greatest."

What it means
"Many researchers," according to Laurance, "remain unconvinced that ongoing disease-linked amphibian declines are being widely instigated by rising global temperatures or associated climatic variables, as proposed by Pounds et al." For one thing, he says that "chytrid-linked amphibian declines have been documented on several continents and at varying times," and that to date, "no single environmental stressor has been identified that can easily account for these numerous population crashes." In his personal view, as he describes it, "it stretches plausibility to argue that the chytrid pathogen is simply an opportunistic, endemic microparasite that has suddenly begun causing catastrophic species declines as a consequence of contemporary global warming."

We agree. As recently noted by Lips et al. (2008), "both field studies on amphibians and on fungal population genetics strongly suggest that Batrachochytrium dendrobatidus is a newly introduced invasive pathogen," which "spreads from its point of origin in a pattern typical of many emerging infectious diseases," and that just happens to have done so within a climatic context of increasing global warmth.

Lips, K.R., Diffendorfer, J., Mendelson III, J.R. and Sears, M.W. 2008. Riding the wave: Reconciling the roles of disease and climate change in amphibian declines. PLoS (Public Library of Science) Biology 6(3): e72. doi:10.1371/journal.pbio.0060072.

Pounds, J.A., Bustamante, M.R., Coloma, L.A., Consuegra, J.A., Fogden, M.P.L., Foster, P.N., La Marca, E., Masters, K.L., Merino-Viteri, A., Puschendorf, R., Ron, S.R., Sanchez-Azofeifa, G.A., Still, C.J. and Young, B.E. 2006. Widespread amphibian extinctions from epidemic disease driven by global warming. Nature 439: 161-167.

Reviewed 20 August 2008