How does rising atmospheric CO2 affect marine organisms?

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Getting the Baseline Right
Greenstein, B.J., Curran, H.A. and Pandolfi, J.M.  1998.  Shifting ecological baselines and the demise of Acropora cervicornis in the western North Atlantic and Caribbean Province: a Pleistocene perspective.  Coral Reefs 17: 249-261.

The authors broach the problem of the "shifting base line syndrome," stating the obvious - but oft-neglected - truth that "it must be demonstrated that the classic reef coral zonation pattern described in the early days of coral reef ecology, and upon which 'healthy' versus 'unhealthy' reefs are determined, are themselves representative of reefs that existed prior to any human influence."

What was done
Systematic censuses of life and death assemblages were conducted on healthy modern patch reefs in the Florida Keys and the Bahamas, and the results were compared to censuses of ancient reef assemblages preserved in Pleistocene limestones in close proximity to the modern reefs.

What was learned
Living patch reefs of the Florida Keys were found to be "representative of patch reefs that flourished prior to any human influence in that area."  In the Bahamas, however, the authors observed a recent rapid decline of A. cervicornis that they describe as "a unique event that contrasts with the long-term persistence of this taxon during Pleistocene and Holocene time."

What it means
The recent "complete die-off of once-dominant Acropora cervicornis and subsequent replacement by Porites porites," which "does not have a Pleistocene precedent," argues strongly against global warming or El Niņo warming as being its cause, since the Pleistocene record is replete with climatic changes of large magnitude - reaching significantly greater warmth than currently prevails on earth - that had almost no effect on this long-term dominant of Caribbean coral reefs.  Consequently, whereas "the lack of long-term data on coral community composition has confounded attempts to determine whether these faunal replacements are natural components of long term ecological cycles or an unprecedented phenomenon resulting from primarily anthropogenic disturbances," it now seems clear that the latter direct assaults of humanity are what have brought about the demise of this particular Caribbean coral.  Global warming, by itself, does not appear to be implicated.

Reviewed 1 July 1999