How does rising atmospheric CO2 affect marine organisms?

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The Resiliency of the Reef-Flat Corals of Ko Phuket, Thailand
Brown, B.E., Clarke, K.R. and Warwick, R.M.  2002.  Serial patterns of biodiversity change in corals across shallow reef flats in Ko Phuket, Thailand, due to the effects of local (sedimentation) and regional (climatic) perturbations.  Marine Biology 141: 24-29.

Brown et al. note that "the scientific literature contains relatively few truly long-term studies of coral communities (Connell, 1997; Connell et al., 1997; Hughes and Connell, 1999)," and that, as a result, "our ability to predict the response of reef communities to either acute or chronic disturbances is rather limited, particularly since there is generally much more focus on immediate impacts rather than on processes involved in damage and recovery (Hughes and Connell, 1999)."  Hence, they did what they could to improve this situation by conducting a long-term study of the type they say is sorely needed.

What was done
The authors conducted a 17-year study of coral reef flats at Ko Phuket, Thailand, in which they assessed coral reef changes in response to elevated sea temperatures in 1991, 1995, 1997 and 1998.

What was learned
"Many corals bleached," in the words of the authors, "during elevated sea temperatures in May 1991 and 1995, but no bleaching was recorded in 1997."  In addition, they report that "in May 1998 very limited bleaching occurred although sea temperatures were higher than previous events in 1991 and 1995 (Dunne and Brown, 2001)."  And when bleaching did take place, they say "it led only to partial mortality in coral colonies, with most corals recovering their color within 3-5 months of initial paling."

What it means
As Adjeroud et al. (2002) have written about their own study, the results of Brown et al. (2003) demonstrate "the importance of understanding the ecological history of reefs (i.e., the chronology of disturbances) in interpreting the specific impacts of a particular disturbance."  For example, Brown et al.'s findings, like those of Adjeroud et al., could readily be interpreted to suggest, in the words of Adjeroud et al., that "most of the coral colonies in place in [1997 and 1998] were those that survived the [1991 and 1995] event[s] or were young recruits derived from those colonies," and that "one may assume that these coral colonies and/or their endosymbiotic zooxanthellae were phenotypically (acclimation) and possibly genotypically (adaptation) resistant to bleaching events (Rowan et al., 1997; Hoegh-Guldberg, 1999)," perhaps as a result of symbiont shuffling [see Symbiont Shuffling in our Subject Index], which phenomenon could well be an effective means for coral colonies to adapt to rising sea temperatures.

What it means
Adjeroud, M., Augustin, D., Galzin, R. and Salvat, B.  2002.  Natural disturbances and interannual variability of coral reef communities on the outer slope of Tiahura (Moorea, French Polynesia): 1991 to 1997.  Marine Ecology Progress Series 237: 121-131.

Connell, J.H.  1997.  Disturbance and recovery of coral assemblages.  Coral Reefs 16: 101-113.

Connell, J.H., Hughes, T.P. and Wallace, C.C.  1997.  A 30-year study of coral abundance, recruitment and disturbance at several sites in space and time.  Ecological Monographs 67: 461-488.

Duane, R.P. and Brown, B.E.  2001.  The influence of solar radiation on bleaching of shallow water reef corals in the Andaman Sea, 1993-98.  Coral Reefs 20: 201-210.

Hoegh-Guldberg, O.  1999.  Climate change, coral bleaching and the future of the world's coral reefs.  Marine and Freshwater Research 50: 839-866.

Hughes, T.P. and Connell, J.H.  2000.  Multiple stressors on coral reefs: a long-term perspective.  Limnology and Oceanography 44: 932-940.

Rowan, R., Knowlton, N., Baker, A. and Jara, J.  1997.  Landscape ecology of algal symbionts creates variation in episodes of coral bleaching.  Nature 388: 265-269.

Reviewed 31 December 2003