What was done
The authors discovered "dense clusters of the vent mussel Bathymodiolus brevior in natural conditions of pH values between 5.36 and 7.29 on the northwest Eifuku volcano, Mariana arc, where liquid carbon dioxide and hydrogen sulfide emerge in a hydrothermal setting," which they studied along with mussels from "two sites in the southwestern Pacific: Hine Hina in the Lau backarc basin and Monowai volcano on the Kermadec arc," where "the same mussel species nestles in cracks and rubble where weak fluid flow emerges."

What was learned
Tunnicliffe et al. identified four-decade-old mussels that had learned to cope with the extreme acidity of these hellish conditions, although their shell thickness and daily shell growth increments were "only about half those recorded from mussels living in water with pH > 7.8." Nevertheless, the mussels were alive and doing what most climate alarmists have claimed such creatures should not be able to do in such conditions. And the six researchers note that the mussels were accompanied by "many other associated species," as reported in the study of Limen and Juniper (2006).

What it means
Tunnicliffe et al. conclude that these several findings attest to "the extent to which long-term adaptation can develop tolerance to extreme conditions." And just how extreme were the conditions in which the mussels lived? Caldeira and Wickett (2003) have calculated the maximum level to which the air's CO2 concentration might rise due to the burning of earth's post-21st century fossil-fuel reserves (2000 ppm), the point in time when that might happen (AD 2300), and the related decline that might be expected to occur in ocean-surface pH (0.7 unit). These results give a time frame of 300 years for organisms to adapt to a pH decline from about 8.1 to 7.4; and considering the much lower pH range in which the mussels studied by Tunnicliffe et al. and the many species studied by Limen and Juniper were living (5.36 to 7.29), there is ample reason to believe that even the worst case atmospheric CO2-induced acidification scenario that can possibly be conceived would not prove a major detriment to most calcifying sea life. Consequently, what will likely happen in the real world should be no problem at all, as is additionally suggested by the many items we have archived in our Subject Index under the headings of Calcification and Evolution.

References
Caldeira, K. and Wickett, M.E. 2003. Anthropogenic carbon and ocean pH. Nature 425: 365.

Limen, H. and Juniper, S.K. 2006. Habitat controls on vent food webs at NW Eifuku Volcano, Mariana Arc. Cahiers de Biologie Marine 47: 449-455.