Abstract
The ability of an organism to alter its physiology in response to environmental conditions offers a short-term defense mechanism in the face of weather extremes resulting from climate change. These often manifest as multiple, interacting drivers, especially pH and temperature. In particular, decreased pH can impose constraints on the biological mechanisms which define thermal limits by throwing off energetic equilibrium and diminishing physiological functions (e.g., in many marine ectotherms). For many species, however, we do not have a detailed understanding of these interactive effects, especially on short-term acclimation responses. Here, we investigated the metabolic plasticity of a tropical subtidal gastropod ( Trochus maculatus ) to increased levels of CO 2 (700 ppm) and heating (+3°C), measuring metabolic performance ( Q 10 coefficient) and thermal sensitivity [temperature of maximum metabolic rate (T MMR ), and upper lethal temperature (ULT)]. Individuals demonstrated metabolic acclimation in response to the stressors, with T MMR increasing by +4.1°C under higher temperatures, +2.7°C under elevated CO 2 , and +4.4°C under the combined stressors. In contrast, the ULT only increased marginally in response to heating (+0.3°C), but decreased by −2.3°C under CO 2 , and −8.7°C under combined stressors. Therefore, although phenotypic plasticity is evident with metabolic acclimation, acute lethal temperature limits seem to be less flexible during short-term acclimation.