Effects of ocean acidification and elevated temperature on shell plasticity and its energetic basis in an intertidal gastropod

Phenotypic plasticity is a mechanism by which organisms can alter their morphology, life history or behaviour in response to environmental change. Here, we investigate shell plasticity in the intertidal gastropod Littorina littorea in response to the ocean acidification and elevated temperature values predicted for 2100, focusing on shell traits known to relate to protection from predators (size, shape and thickness) and resistance to desiccation (aperture shape). We also measured and desiccation rates (measured as percentage water loss). Ocean acidification was simulated by bubbling carbon dioxide into closed-circuit tanks at concentrations of 380 and 1000 ppm, giving respective pH levels of 8.0 and 7.7; temperatures were set at 15 or 20 C. Both low pH and elevated temperature disrupted the overall investment in shell material; snails in acidified seawater and elevated temperature in isolation or in combination had lower shell growth rates than control individuals. The percentage increase in shell length was also lower for individuals kept under combined acidified seawater and elevated temperature, and the percentage of shell thickness increase at the growing edge was lower under acidified and combined conditions. Shells were also more globular (i.e. had lower aspect ratios) under elevated temperature and lower pH. Desiccation rates were lower at low pH and high temperature. Counter to predictions, water loss did not relate to shell biometric measures but was negatively correlated with adenosine triphosphate (ATP) concentrations. Finally, ATP concentration was positively correlated with shell thickening and weight, confirming the idea that negative effects of exposure to elevated pCO(2)/low pH and elevated temperature on shell morphology may occur (at least in part) through metabolic disruption.