The role of preconditioning in ocean acidification experiments: a test with the intertidal isopod Paradella dianae

Environmental alterations are accelerating worldwide and the rate of change in ocean chemistry is predicted to happen so rapidly that it is unclear how marine ecosystems will respond. It is hypothesized that the phenotypic plasticity or acclimation capacity of an individual provides a buffer against environmental change; however, this plasticity depends on the speed at which the change occurs. Ocean acidification studies have found direct and acute responses from organisms exposed to elevated CO2 levels. Now, the challenge lies in integrating acclimation into experimental design in short-term studies, requiring proper preconditioning setups. Here we experimentally show that different preconditioning approaches produce different physiological and behavioral responses in the intertidal isopod Paradella dianae. Isopods were impaired when immediately exposed to elevated CO2 levels relative to individuals that were gradually acclimated to high CO2 concentrations. Abruptly introducing organisms to severe changes in CO2 conditions can produce confounding effects of short-term stress with acclimated responses to long-term shifts in ocean chemistry. By exposing organisms to sudden changes in CO2 concentrations, we are forcing immediate physiological stress reactions that could be independent of exposure to specific CO2 levels. We discuss how integrating acclimation in experimental design can help provide more accurate predictions about the impact of ocean acidification on marine ecosystems.