Background
The authors say "it has been suggested that organisms presently surviving in highly variable environments are likely to be more robust to ocean acidification," citing Moulin et al. (2011) and Raven (2011); and they suggest that if this be the case, "the ability of organisms to tolerate significant pH/pCO2 fluctuations may be a result of adaptation (a genetic trait shared by the population) and/or acclimation (owing to phenotypic plasticity of the individual)."

What was done
"To test this hypothesis," in the words of Egilsdottir et al., "the effect of elevated pCO2 was investigated in the articulated coralline red alga Corallina elongata from an intertidal rock pool on the north coast of Brittany (France), where pCO2 naturally varied daily between 70 and 1000 ľatm." This was done by growing the algae at four different pCO2 values (380, 550, 750 and 1000 ľatm) in laboratory mesocosms and measuring several different physiological responses of the coral.

What was learned
The French and Icelandic researchers report that "algae grown under elevated pCO2 formed fewer new structures and produced calcite with a lower mMg/Ca ratio relative to those grown under 380 ľatm." However, they also report that "respiration, gross primary production and calcification in light and dark were not significantly affected by increased pCO2."

What it means
As a result of their several findings, Egilsdottir et al. conclude that their study "supports the assumption that C. elongata from a tidal pool, where pCO2 fluctuates over diel and seasonal cycles, [are] relatively robust to elevated pCO2." And they also thus state that these observations portend "a greater resilience" of such organisms to the projected "highly variable pH/pCO2 environments of future ocean acidification."

References
Moulin, L., Catarino, A.I., Claessens, T. and Dubois, P. 2011. Effects of seawater acidification on early development of the intertidal sea urchin Paracentrotus lividus (Lamarck 1816). Marine Pollution Bulletin 62: 48-54.

Raven, J.A. 2011. Effects on marine algae of changed seawater chemistry with increasing atmospheric CO2. Biology and Environment Proceedings of the Royal Irish Academy 111B: 1-17.