A study published in the journal PLoS One (Open Access: download here) discusses the role of a coral's thermal history and previous exposure to temperature stress as increasing the resistance of corals to future temperature stress events. (You can read a nice PR right-up from the University of British Columbia, here).
The study used corals in the Gilbert Islands in the Republic of Kiribati, and found that corals subject to large changes in temperature were more resilient to bleaching than those corals in areas where temperature stress was less common, or the environment was less thermally variable. This is very interesting! What it suggests is that corals exposed to variable conditions (or greater periods of warming) are able to tolerate this warming better than those corals in what we would characterize as ideal, non-stressed conditions.
In the context of global warming, we are anticipating a 1-3 degree Celsius increase in ocean temperature. A big talking point in coral biology (and many other arenas) are whether organisms will simply go extinct or have much reduced populations, or can organisms adapt to rapid man-made climate change. A key to this "adaptation" (the evolutionary changes in an organism that are passed on to subsequent generation and driven by natural selection) may be the ability for corals to acclimate or acclimatize to stressful conditions. So, what this study shows us is that corals are able to acclimatize to environmental stress--i.e., change their metabolism, concentrate compounds, alter gene expression--and this short-term process allows corals to be resilient to stressful conditions. In a way this can be likened to "cross training" for an event, like a marathon. If you have been exposed to stressful conditions and your body has turned on its physiological, biochemical, and genetic machinery to respond to period of stress then the organisms may be able to out perform those organisms that have not had the pre-exposure.
A great quote from the first author Dr. Jessica Carilli here: “Even through the warming of our oceans is already occurring, these findings give hope that coral that has previously withstood anomalously warm water events may do so again. While more research is needed, this appears to be good news for the future of coral reefs in a warming climate.”
...and I can stand behind that.