Elevated levels of atmospheric CO2 have had the unintended effect of acidifying the world’s oceans by at least 0.1 pH unit since the beginning of the industrial revolution. Current models of the effects of continued CO2 release anticipate a further increase in ocean acidity by 0.14 to 0.4 pH units by the end of this century. Numerous marine organisms with calcareous shells or exoskeletons are expected to undergo deleterious effects, including shell or exoskeletal dissolution or calcification with increased metabolic costs. While many studies have documented potential effects of ocean acidity on adult calcareous organisms, less work has focused on embryonic or developmental changes. Alterations in ocean biochemistry can affect metabolic processes beyond calcification, and our investigations into the development of the local intertidal mudsnail, Nassarius obsoletus, led us to hypothesize that rising ocean acidity would increase incidents of larval shell decalcification, decrease larval growth rates, and induce precocious metamorphosis. As an initial study of potential effects of future acidic conditions on larval N. obsoletus, we raised larvae in seawater adjusted to lower than normal pH levels with hydrochloric acid (HCl), measured larval growth every 5 days in 15 randomly selected individuals from each culture, and conducted experiments on larval metamorphosis in physiologically competent larvae. We found no major trend in growth patterns of larvae from pH 8.2 to 7.7. However, results from a number of pharmacological experiments demonstrated that larvae grown in acidic conditions metamorphose more readily than controls. Our investigations are far from a definitive exploration of the effects of oceanic acidity on the development of this marine mollusc, but our data suggest that key developmental processes in marine invertebrates may be influenced in unexpected ways by continued climatic changes.
Leise E. M., Washburn J. T., Long J., Bridgewater B. & Shah N., 2014. Acidic seawater can promote larval metamorphosis in the marine mud snail, Nassarius obsoletus. Journal of North Carolina Academy of Science 130(2):65-71. Article (subscription required).
It is unfortunate that the terminology used here is misleading. The definition of “acidic” in the Oxford English dictionary is “having the properties of an acid; having a pH of less than 7″. Despite the process of ocean acidification, the oceans are alkaline (pH higher than 7) and will not become acidic in the foreseeable future. Hence, the “acid” or “acidic” should not be used when referring to seawater. Note that there are few exceptions, seawater can be acidic in the immediate vicinity of CO2 vents or in purposeful perturbation experiments.