Current and future ocean chemistry negatively impacts calcification in predatory planktonic snails

Planktonic gastropods mediate an important flux of carbonate from the surface to the deep ocean. However, we know little about the response of atlantid heteropods, the only predatory, aragonite shelled zooplankton, to ocean acidification (OA), and they are not incorporated in any carbonate flux models. Here we quantify the effects of OA on calcification and gene expression in atlantids across three pH scenarios: mid-1960’s, ambient, and future 2050 conditions. Atlantid calcification responses to decreasing pH were negative, but not uniform, across the three scenarios. Calcification was reduced from mid-1960s to ambient conditions, and longer shells were grown under 2050 conditions. Differential gene expression indicated a stress response at both ambient and future conditions, with down-regulation of growth and biomineralization genes with decreasing pH. Our results suggest that ocean chemistry in the South Atlantic is already limiting atlantid calcification, and that exposure to near-future OA triggers rapid shell growth under stress.