How does rising atmospheric CO2 affect marine organisms?

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A 35-Year History of Caribbean Coral Reefs
Schutte, V.G.W., Selig, E.R. and Bruno, J.F. 2010. Regional spatio-temporal trends in Caribbean coral reef benthic communities. Marine Ecology Progress Series 402: 115-122.

Climate alarmists are quick to contend that earth's coral reefs are headed to hell in a handbasket, as it were, with Pelejero et al. (2010) arguing that the oceanic changes we are facing today, in pCO2 and in pH, "are happening ~100-times faster than during glacial-interglacial transitions," and that "the average surface pH levels that oceans have reached today are already more extreme than those experienced by the oceans during the glacial-interglacial changes and beyond, probably being more extreme than at any time during the last 20 million years."

What was done
In a study designed to determine regional-scale trends in coral cover on Caribbean reefs over the last 35 years in each of seven sub-regions -- which effort could logically be expected to shed light on the impacts of the highly-hyped oceanic changes lamented by Pelejero et al. -- Schutte et al., as they describe it, "analyzed the spatio-temporal trends of benthic coral reef communities in the Caribbean using quantitative data from 3,777 coral cover surveys of 1,962 reefs from 1971-2006."

What was learned
Schutte et al. determined that from 1971 to 1980, annual Caribbean-wide coral cover averages were highest and without trend, with all but two values falling between 30 and 40%. Then came the largest one-year decline in coral cover of the entire record -- a precipitous drop from about 37% to 12% between 1980 and 1981 that corresponded in time, in their words, "with the beginning of the Caribbean-wide Acropora spp. white band disease outbreak," after which (from 1982 to 2006) they note that "coral cover has been relatively stable," with values ranging from about 15% to 22%.

What it means
Clearly, the temporal history of Caribbean coral cover change does not bear any resemblance to the gradual and continuous decline that could have been expected from the concomitant increase in oceanic pCO2 and decrease in pH. Indeed, after suffering the sharp one-year decline caused by the white band disease outbreak, coral cover once again stabilized, which phenomenon, in the words of Schutte et al., "could be interpreted as relatively good news" -- which it truly is -- although they state that this pattern "could also be a temporary plateau preceding a potential collapse in coral cover." Then, again, we could just as easily say it could also be a temporary plateau preceding a potential increase in coral cover. (Isn't speculation wonderful?)

Pelejero, C., Calvo, E. and Hoegh-Guldberg, O. 2010. Paleo-perspectives on ocean acidification. Trends in Ecology and Evolution: 10.1016/j.tree.2010.02.002.

Reviewed 9 June 2010