How does rising atmospheric CO2 affect marine organisms?

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To the Big Bleaching and Back Again
Kayanne, H., Harii, S., Ide, Y. and Akimoto, F.  2002.  Recovery of coral populations after the 1998 bleaching on Shiraho Reef, in the southern Ryukyus, NW Pacific.  Marine Ecology Progress Series 239: 93-103.

What was done
Coral cover within the reef flat of Shiraho Reef, Ishigaki Island (situated at the southernmost end of the Ryukyus Islands of Japan) was assessed just before, during, and six times subsequent to the unprecedented bleaching event that began in early July of 1998 and ended in early October of that year.

What was learned
Different corals responded differently. The authors report that "massive Porites were susceptible to bleaching, but regained their algae after the bleaching and sustained their coverage."  On the other hand, they say that branching Porites, Montipora and Acropora corals experienced significant mortality of 41.1%, 55.4% and 82.4%, respectively, and that approximately two-thirds of the surviving corals were completely or partly bleached.  Nevertheless, coverage of large patches of the branching Montipora coral, which were initially reduced by 66%, recovered to pre-bleaching levels after just two years.

What it means
The authors note that "the recovery of corals to their pre-bleaching levels has been inferred to take from 10 to 30 years for damaged coral populations and from 5 to 10 years for bleached corals that do not die (Hoegh-Guldberg, 1999; Wilkinson et al., 1999)."  However, Shiraho Reef, as they report, "is recovering at an unexpectedly fast rate," which is almost an understatement, considering the fact that massive Porites corals recovered within but a matter of months after cessation of bleaching and that the highly- decimated branching Montipora corals recovered within a mere two years.

It would appear from these observations and others (Normile, 2000) that, in the words of the authors, "even susceptible species have a high potential to regain zooxanthellae after bleaching or to recover after mortality," and, we might add, at a much faster rate than many marine biologists had once thought possible.

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

Normile, D.  2000.  Some coral bouncing back from El Niņo.  Science 288: 941-942.

Wilkinson, C., Linden, O., Cesar, H., Hodgson, G., Rubens, J. and Strong, A.E.  1999.  Ecological and socioeconomic impacts of 1998 coral mortality in the Indian Ocean: an ENSO impact and a warning of future change?  Ambio 28: 188-196.

Reviewed 13 November 2002