How does rising atmospheric CO2 affect marine organisms?

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Slowdown in Rate of Caribbean Coral Decline: What's Causing It?
Buddemeier, R.W. and Ware, J.R.  2003.  Coral reef decline in the Caribbean.  Science 302: 391-392.

Gardner, T.A., Cote, I.M., Gill, J.A., Grant, A. and Watkinson, A.R.  2003b.  Response.  Science 302: 392-393.

In a meta-analysis published in Science, Gardner et al. (2003a) report a massive region-wide decline of corals across the entire Caribbean basin over the past three decades, noting, however, that "the rate of coral loss has slowed in the past decade compared to the 1980s."  In addition, they say "there is no convincing evidence yet that global stressors (e.g. temperature-induced bleaching and reduced rates of carbonation via enhanced levels of atmospheric CO2) are responsible for the overall pattern of these recent coral declines."  Instead, they lay the blame at the feet of "local factors originating both naturally (e.g. disease, storms, temperature stress, predation) and anthropogenically (e.g. over-fishing, sedimentation, eutrophication, habitat destruction)," which is pretty much the view we take of the subject.

What was done
Buddemeier and Ware take issue with Gardner et al.'s (2003a) assessment of the issue, stating "the possibility of recent amelioration and the inferences about the relative roles of climatic and local human factors should be viewed with caution," adding "we feel that climate-related factors are too casually dismissed."  In response to this challenge to their conclusions, Gardner et al. (2003b) reiterate their firm belief that "although factors directly related to climate change (e.g., bleaching) have affected Caribbean corals at subregional scales, their role in contributing to observed coral declines across the entire region is not yet detectable."  They go on to add, however, that "the ability of Caribbean coral reefs to cope with the threat of future climate change may be irretrievably compromised," obviously as a consequence of local anthropogenic factors that have severely weakened them, which is also our position on the topic.

What was learned
Different scientists often interpret the same evidence quite differently.  In the case in point, the issue is a highly controversial one, which tends to make agreement even more difficult to achieve.

What it means
In spite of the fact the Gardner et al. (2003a) meta-analysis was based on data obtained from a total of 263 sites described in 65 scientific studies, that massive body of evidence is insufficient to adequately rank the relative importance of the roles played by local and global anthropogenic factors in the historical reduction of Caribbean coral cover.  Hence, it is by no means a "stalling tactic" to say "more research is needed."  What is in hand is clearly insufficient to resolve the issue to the satisfaction of all concerned.

Gardner, T.A., Cote, I.M., Gill, J.A., Grant, A. and Watkinson, A.R.  2003a.  Long-term region-wide declines in Caribbean corals.  Science 301: 958-960.

Reviewed 10 December 2003