Background
Writing of corals, the authors say "it has been shown that it is possible for colonies to acclimatize to increased temperatures and high irradiance levels so that they are able to resist bleaching events when they occur." And they note, in this regard, that "threshold temperatures that induce coral bleaching-related mortality vary worldwide -- from 27°C in Easter Island (Wellington et al., 2001) to 36°C in the Arabian Gulf (Riegl, 1999) -- according to the maximum water temperatures that are normal in the area, implying a capacity of corals and/or zooxanthellae to acclimatize to high temperatures depending on their environment."

What was done
In further exploration of this phenomenon, Grimsditch et al. examined "bleaching responses of corals at four sites (Nyali, Mombasa Marine Park, Kanamai and Vipingo) representing two distinct lagoon habitats on the Kenyan coast (deeper and shallower lagoons)." This was done for the coral community as a whole, while zooxanthellae densities and chlorophyll levels were monitored for three target species (Pocillopora damicornis, Porites lutea and Porites cylindrica) during a non-bleaching year (2006) and a mild bleachig year (2007).

What was learned
The four researchers report that "during the 2007 bleaching season, corals in the shallow lagoons of Kanamai and Vipingo were more resistant to bleaching stress than corals in the deeper lagoons of Mombasa Marine Park and Nyali," which suggests, in their words, that "corals in the shallower lagoons have acclimatized and/or adapted to the fluctuating environmental conditions they endure on a daily basis and have become more resistant to bleaching stress."

What it means
These results bear further witness to the fact that earth's corals have the ability to evolve in such a way as to successfully adjust to changing environmental conditions that when first encountered may prove deadly to a significant percentage of their populations. Those individuals genetically blessed to better withstand various stresses weather the storm, so to speak, to grow and widely proliferate another day.

References
Riegl, B. 1999. Corals in a non-reef setting in the southern Arabian Gulf (Dubai, UAE): Fauna and community structure in response to recurring mass mortality. Coral Reefs 18: 63-73.

Wellington, G.M., Glynn, P.W., Strong, A.E., Nauarrete, S.A., Wieters, E. and Hubbard, D. 2001. Crisis on coral reefs linked to climate change. EOS, Transactions, American Geophysical Union 82: 1,7.