Paper Reviewed
Duarte, C., Navarro, J.M., Acuña, K., Torres, R., Manriquez, P.H., Lardies, M.A., Vargas, C.A., Lagos, N.A. and Aguilera, V. 2015. Intraspecific variability in the response of the edible mussel Mytilus chilensis (Hupe) to ocean acidification. Estuaries and Coasts 38: 590-598.

In the words of Duarte et al. (2015), "recent studies have shown that the responses of [marine calcifying organisms] to ocean acidification can vary significantly among species," yet they note that "much less is known concerning the intraspecific variability." Thus, in an effort to fill this knowledge void, the team of nine Chilean researchers set out to examine the impacts of ocean acidification on individuals of two populations of Mytilus chilensis, an edible mussel that is widely cultivated in Chile

M. chilensis inhabits a wide range of environmental conditions across a large geographic region (from 37°S to 73°S off the coast of Chile), where populations are "naturally exposed to highly variable pH conditions." For their study, Duarte et al. collected juvenile mussels from Yaldad and Huelmo bays, the former of which receives a steady input of freshwater from a terminating river. The mussels were transferred into a laboratory setting and subjected to different seawater pH treatments (8.1, 7.9 and 7.7) for a period of 20 days after which they were evaluated for net calcification, growth rate and shell dissolution.

With respect to their findings, the authors report there was "no significant effect of CO2 concentrations on net calcification" for individuals from Yaldad Bay. In contrast, net calcification was significantly higher at the control pH compared to specimens in the two reduced pH treatments from Huelmo Bay. Similar findings were reported for growth rate, which was not significantly different among the three pH treatments for Yaldad Bay mussels. There was, however, a significant reduction among specimens in the lowest pH treatment compared with the highest for Huelmo Bay. With respect to shell dissolution, which was measured using shells from deceased specimens, the scientists say it "was not affected by CO2 concentrations." However, dissolution was larger in magnitude among the Huelmo Bay mussels than those from Yaldad Bay. Lastly, they note there was an "absence of mortality" among all treatments.

In commenting on their findings, the Chilean researchers opine that the "lower susceptibility of the net calcification to ocean acidification recorded in the Yaldad Bay mussels could have resulted from an adaptation of these organisms to the freshwater inputs (from Yaldad River), which may produce naturally lower pH values and low carbonate ion contents" to which these organisms were exposed in the laboratory. Nevertheless, as they concluded, "the results of this study corroborate the increasing evidence that shows that substantial intraspecific variation in response to increments of CO2 levels may also occur, which warns [of] the danger of generalizing the results obtained even within the same species." Acidification alarmists take note!