Summary of model parameters and their sources.

Organism-level bioenergetics models (OBMs) are an emerging tool for predicting consequences of climate change on organism growth in ecological systems. Global changes in ocean and atmospheric temperature may affect organisms that experience both environments, such as those living in intertidal systems. The acorn barnacle, Balanus glandula, is prevalent throughout the intertidal zone in the Eastern Pacific, and laboratory experiments demonstrate that feeding rates and metabolic costs are sensitive to temperature. We hypothesized that, based on these thermal responses, aerial and aquatic warming will decrease B. glandula growth in a field environment because of increased costs and reduced feeding. We measure environmental conditions (aerial and aquatic temperature) at three intertidal heights over two 6-month intervals and compare observed growth to growth estimates based on a Numerical Scope for Growth model. Initial work indicates that growth is less sensitive to shore height than predicted by lab-based physiological rates alone, so we estimate a compensation factor (Z) that captures non-linear changes in feeding with shore height when fitting the model to all three elevations and the two intervals. This full model predicts that, in this environment, aquatic warming will counteract increased costs of aerial warming, by virtue of increased feeding at warmer temperatures. This work advances OBMs by combining the effects of multiple decoupled thermal responses (e.g., feeding, respiration) in multiple contexts (aerial, aquatic), drawing on established model selection and “divide and conquer” techniques, and identifying sources of uncertainty in the model. This work indicates that future intertidal OBMs may benefit from an improved characterization of feeding behavior, including empirical estimates of elevation-dependent feeding compensation.