How does rising atmospheric CO2 affect marine organisms?

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The Distant Past is a Key to the Recent Past
Greenstein, B.J., Harris, L.A. and Curran, H.A.  1998.  Comparison of recent coral life and death assemblages to Pleistocene reef communities: Implications for rapid faunal replacement on recent reefs.  Carbonates & Evaporites 13: 23-31.

What was done
The authors compared the taxonomic structure of live and dead coral communities on a modern patch reef, which is currently undergoing a community transition, to late Pleistocene fossil coral assemblages.

What was learned
The data revealed a recent decline in thickets of Acropora cervicornis, as evidenced by their abundance in the "death assemblage," and a concurrent increase in Porites porites, as evidenced by their abundance in the "life assemblage."  In comparing these results with those obtained from the "fossil assemblage," they concluded that "the present Caribbean-wide decline of A. cervicornis is without historical precedent" and that it "contrasts with the long-term persistence of this taxon during Pleistocene and Holocene Optimum time," even during periods of "intensifying cycles in climate and sea level" that recurred again and again throughout a roughly one-million-year time period.

What it means
This study suggests that if little change in coral community structure occurred over Holocene and earlier times, when we know it was often warmer than it is now, the current die-off of A. cervicornis must not be due to global warming.  Instead, it must be a direct consequence of some human-induced alteration of the physical or chemical characteristics of the reef environment.  In the words of the authors, "although the A. cervicornis-dominated coral association persisted during Pleistocene climatic fluctuations, it is apparently vulnerable to the array of perturbations currently being inflicted on it."

Reviewed 1 July 1999