Predicting the effect of short and long-term thermal body temperature on the energy balance of intertidal speciesMacroecology

Romina Barbosa¹, Cedric Bacher², Fred Jean³, Yoann Thomas⁴

¹University of Victoria, Canada - ²Ifremer, France - ³LEMAR, IUEM,France - ⁴IRD, France

In this study, we evaluated how microhabitats’ thermal differences, driven by microhabitat conditions, affect the short and long-term energy balance of M. galloprovincialis and ultimately potential population fitness. Specifically, we tested two hypotheses: 1) individuals inhabiting the intertidal gradient are restricted to areas below the upper intertidal where maintenance overpasses the energy acquired from assimilated food, and 2) energetic demand for metabolic maintenance tends to decrease the potential population fitness in microhabitats oriented to the south and at higher intertidal positions. To reach of goal, we estimated the mussels’ body temperature living in aggregations considering the effect of microscale (20 cm) solar radiation, wind shear, and air temperature, as well as cloud cover and the surrounding topography in an entire rocky shore. We classified and aggregated the predicted body temperature by microhabitat type (depending on its substrate slope, orientation, and intertidal height position) and used these, together with food availability along the intertidal gradient as input for a DEB model. Our results quantitatively demonstrated the main effect of food availability on the short-term energy balance of the species, which determined the upper limit of distribution of mussels in our study site, besides affecting the individual’s traits such as size. Thus, microhabitats at different intertidal positions drive the main differences in mussels’ performance in the short term. In the long term, both food availability and body temperature history across microhabitats determined differences in reproductive capacity and growth, and survival due to shrinking periods. Mussels inhabiting microhabitats oriented to the south were predicted to have a higher contribution to the population fitness than mussels inhabiting north-oriented microhabitats. These results explicitly demonstrate how microhabitat differences in combined intertidal height and orientation features could determine the contribution of individuals to the population fitness.