Background
The authors write that "reef-building corals have experienced global declines resulting from bleaching events sparked by pulses of warm-water exposure," but they note that "corals in naturally warm environments can have high resistance to bleaching temperatures and can survive heat exposure that would bleach conspecifics in cooler microclimates," citing Oliver and Palumbi (2009, 2011). And they add that the "recent discovery of populations of acidification-resistant corals show that physiological or evolutionary mechanisms of environmental accommodation exist," citing Fabricius et al. (2011) and Shamberger et al. (2014).

What was done
Working with corals in adjacent back-reef pools in the U.S. National Park of American Samoa on Ofu Island, where they sought "to determine the mechanisms of temperature tolerance," as they describe it, Palumbi et al. "reciprocally transplanted corals between reef sites experiencing distinct temperature regimes and tested subsequent physiological and gene expression profiles," in order to see how any newly-acquired temperature tolerance may have been obtained.

What was learned
The four U.S. researchers report that "local acclimatization and fixed effects, such as adaptation, contributed about equally to heat tolerance and are reflected in patterns of gene expression," with the result, as they continue, that "in less than two years, acclimatization achieves the same heat tolerance that we would expect from strong natural selection over many generations for these long-lived organisms."

What it means
Noting that the experimental results they obtained for the fast-growing shallow-water species they studied "show both short-term acclimatory and longer-term adaptive acquisition of climate resistance," which "allowed them to inhabit reef areas with water temperatures far above their expected tolerances," Palumbi et al. conclude that "adding these adaptive abilities to ecosystem models is likely to slow predictions of demise for coral reef ecosystems."

References
Fabricius, K.E., Langdon, C., Uthicke, S., Humphrey, C., Noonan, S., De'ath, G., Okazaki, R., Muehilehner, N., Glas, M.S. and Lough, J.M. 2011. Losers and winners in coral reefs acclimatized to elevated carbon dioxide concentrations. Nature Climate Change 1: 165-169.

Oliver, T.A. and Palumbi, S.R. 2009. Distributions of stress-resistant coral symbionts match environmental patterns at local but not regional scales. Marine Ecology Progress Series 378: 93-103.

Oliver, T.A. and Palumbi, S.R. 2011. Do fluctuating temperature environments elevate coral thermal tolerance? Coral Reefs 30: 429-440.

Shamberger, K.E.F., Cohen, A.L., Golbuu, Y., McCorkle, D.C., Lentz, S.J. and Barkley, H.C. 2014. Diverse coral communities in naturally acidified waters of a Western Pacific Reef. Geophysical Research Letters 41: 499-504.