How does rising atmospheric CO2 affect marine organisms?

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A 16-Year History of Coral Bleaching in Moorea, French Polynesia
Volume 17, Number 2: 8 January 2014

Pratchett et al. (2013) recently developed a history of variations in coral bleaching among four key genera of reef-building corals (Acropora, Montipora, Pocillopora and Porites) in Moorea, French Polynesia, wherein they focused on four mass-bleaching events that occurred there in 1991, 1994, 2002 and 2007, documenting the history of the bleaching susceptibility of each of the four coral genera in each of the four events in order to see what they could learn in so doing.

In describing their findings, the four researchers reported that "Acropora and Montipora consistently bleached in far greater proportions than Pocillopora and Porites." However, they say there was "an apparent and sustained decline in the proportion of colonies that bleached during successive bleaching events, especially for Acropora and Montipora." In 2007, for example, only 77% of Acropora colonies bleached compared with 98% in 1991. And although they acknowledge that "temporal variation in the proportion of coral colonies bleached may be attributable to differences in environmental conditions among years," they say that "alternately, the sustained declines in bleaching incidence among highly susceptible corals may be indicative of acclimation or adaptation."

"One possible explanation for these findings," in the words of Pratchett et al., "is that gradual removal of highly susceptible genotypes (through selective mortality of individuals, populations, and/or species) is producing a coral assemblage that is more resistant to sustained and ongoing ocean warming," and that "there is some capacity for adaptation, which will delay devastating effects of global climate change."

Concomitantly, however, they note that outbreaks of crown-of-thorns starfish (Acanthaster placi) "may have altogether different selective forcing on coral population and communities." And, therefore, they say that although "the capacity for scleractinian corals to adjust to, and cope with, ongoing increases in ocean temperatures may be appreciable," citing Glynn (1991), Maynard et al. (2008) and Guest et al. (2012), they add that "in order to maximize adaptive capacity to climate change it will continue to be important to minimize the diversity, frequency and severity of other anthropogenic disturbances that also affect coral reef organisms."

This is good advice, indeed, for if species-specific, genetically-determined, and life-sustaining processes in corals are capable of enabling them to satisfactorily cope with various aspects of climatic change, mankind has only its own disturbing of local coastal environments with which it needs to deal. If we can refrain from our local environment-degrading actions, nature can well take care of itself.

Sherwood, Keith and Craig Idso

Glynn, P.W. 1991. Coral reef bleaching in the 1980s and possible connections with global warming. Trends in Ecology and Evolution 6: 175-179.

Guest, J.R., Baird, A.H., Maynard, J.A., Muttaqin, E., Edwards, A.J., Campbell, S.J., Yewdall, K., Affendi, Y.A. and Chou, L.B. 2012. Contrasting patterns of coral bleaching susceptibility in 2010 suggest an adaptive response to thermal stress. PLOS ONE 7: e33353.

Pratchett, M.S., McCowan, D., Maynard, J.A. and Heron, S.F. 2013. Changes in bleaching susceptibility among corals subject to ocean warming and recurrent bleaching in Moorea, French Polynesia. PLOS ONE 8: e70443.

Maynard, J.A., Anthony, K.R.N., Marshall, P.A. and Masiri, I. 2008. Major bleaching events can lead to increased thermal tolerance in corals. Marine Biology 155: 173-182.