Background
The authors note that ocean acidification due to rising atmospheric carbon dioxide is claimed by many to be a threat to calcifying marine organisms; and they state that when ocean acidification is combined with physiological stress caused by concomitantly rising sea surface temperatures, "shifts in community structure and accelerating degradation of coral reef ecosystems may result." Well so they may; but do they? That is the question Helmle et al. address in their enlightening new paper.

What was done
Coral cores were collected in May of 1997 and June of 1998 from seven Montastraea faveolata colonies located in the upper Florida Keys (USA), where they "were drilled at the location of maximum vertical growth of the colony." Then, chronologies were constructed from the annual density bands found in the cores; and it was determined that all of them had a 60-year common period from 1937 to 1996. And for these cores, annual extension, density and calcification rates were obtained and analyzed, to see how they varied over this period of intensifying warming and acidification of the global ocean.

What was learned
The five U.S. scientists report that their data show "no evidence of significant age effects" over the 1937-1996 period for either extension, density or calcification.

What it means
In discussing their findings, Helmle et al. say they demonstrate that "the measured corals have historically been able to maintain rates of extension and calcification over the 60-year period from 1937 to 1996 under the combination of local environmental and climatic changes." They also note that calcification rates were positively related to sea surface temperature, "similar to results for Porites corals from Tahiti (Bessat and Buigues, 2001) and the Great Barrier Reef (Lough and Barnes, 1997)," but they say that the Florida results only explained about 7% of the annual calcification variability as opposed to ~30% at the Pacific locations.

As for why the Florida Keys corals have fared so well, when climate alarmists claim "we're on the eve of destruction," Helmle et al. write that the answer could be that "massive reef-building corals are not as susceptible to declines in Ωarag [aragonite saturation state] as demonstrated by laboratory experiments; local processes, such as high seasonal variation in Ωarag in the Florida Keys, may be temporarily enabling these corals to maintain their historical rates of calcification; the role of Ωarag in controlling calcification is masked amidst considerable natural inter-annual variability; or the actual in situ reef-site carbonate chemistry is decoupled from the oceanic values, which could occur as a result of shifts in benthic community metabolism, mineral buffering and/or coastal biogeochemical processes."

And, we would add, Mother Nature likely has a lot more tricks than these up Her sleeves.

References
Bessat, F. and Buigues, D. 2001. Two centuries of variation in coral growth in a massive Porites colony from Moorea (French Polynesia): a response of ocean-atmosphere variability from south central Pacific. Palaeogeography, Palaeoclimatology, Palaeoecology 175: 381-392.

Lough, J.M. and Barnes, D.J. 1997. Several centuries of variation in skeletal extension, density and calcification in massive Porites colonies from the Great Barrier Reef: A proxy for seawater temperature and a background of variability against which to identify unnatural change. Journal of Experimental and Marine Biology and Ecology 211: 29-67.