Tuesday, February 23, 2010

Will Coral Reefs Disappear? Results from AAAS Symposium

The Guardian has a short summary of some of the presentations in our Sunday symposium at AAAS organized by Joan Kleypas. The headline "World's coral reefs could disintegrate by 2100" comes out of field and modeling work presented by Jacob Silverman about the balance of calcium carbonate production through coral calcification of corals and dissolution through bio-erosion (fish, urchins) and higher CO2 levels. Silverman's work is described in this 2009 paper in Geophysical Research Letters.

The talks on the role different bioeroders, carbonate budgets, and a Bermuda case study, lent support Silverman's results. Aline Tribollet's work on "microborers" that erode reefs and Kim Yates work on carbonate sediments suggested that Silverman's model could be a bit conservative. Andreas Andersson's work showed that Bermuda's high latitude reefs may be one of the canaries in the carbonate coal mine.

The headline may give the mistaken impression that there could be absolutely no coral rock left on the planet in 2100. Under the high CO2 conditions, the results suggest reefs would be dissolving faster than they build, leading to reductions in habitat complexity ("flattening" of reefs) over time. Add in the warming-induced bleaching reducing the living coral cover, and by 750 ppm CO2, reached in 2100 in a business-as-usual scenario, the area of living, calcifying reef will be negligible. If theses projections are correct, there will still be dead reef - i.e. rock - but it will be on net weakening and dissolving.

In the Guardian article, I'm quoted as saying "Even if we froze emissions today, the planet still has some warming left in it. That's enough to make bleaching dangerously frequent in reefs worldwide". That line comes from the results of this study published in PLoS-One last year - it's open access, so anyone can download a copy. The important caveat is that acclimation and adaptation by corals could postpone the forecast. For more on those dynamics, I recommend reading this post or the article itself.

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