Variation in the behavioral tolerance of congeneric marine snails to low-pH exposure

Abstract

The ocean is acidifying, with multiple consequences for coastal organisms. However, species may differ in their sensitivities. Some taxa may find future conditions mildly stressful or even advantageous, while others will persist only through acclimatization or genetic adaptation. An open question is whether such variation in the sensitivity of species to ocean acidification relates to their evolutionary histories of exposure to reduced pH. Here, we explored this unknown through an investigation of differences in pH tolerance of 2 shoreline gastropods, the black turban snail Tegula funebralis and its congener, the brown turban snail T. brunnea. These species occupy distinct vertical distributions on rocky shores, each subject to different extremes in low pH. We assayed the extent to which low pH degrades the flight behavior of each species in response to the predatory sea star Pisaster ochraceus. Across a range of pH, the tidepool-inhabiting T. funebralis exhibited less behavioral disruption than T. brunnea at any given pH value but also experienced impairment at a pH characteristic of the present-day minimum in its habitat (7.1 pH). The latter pattern suggests T. funebralis operates near what may be a fixed tolerance limit to low pH. T. funebralis also exhibited hints of elevated intraspecific variation in its behaviors, which could imply scope for selection to act. Deeper-dwelling T. brunnea, in contrast, showed little sensitivity to present-day pH minima found where it lives (7.6 pH) and displayed less variation upon which selection might operate. These results provide a initial framework for investigations into the capacity of species of differing evolutionary histories to cope with future ocean acidification.