Microhabitat temperature variation combines with physiological variation to enhance thermal resilience of the intertidal mussel Mytilisepta virgata

1. Predicting the effects of rising temperature entails measuring both habitat thermal characteristics and the physiological variation of the species as it relates to this microhabitat variation; these two types of measurements can generate what is termed a 'physiological landscape' for the species. Mapping the micro-scale physiological landscape across space and time, rather than relying on large-scale averages of temperature and means of thermal limits in a species, can allow more accurate estimates of an organism's sensitivity to temperature change and support development of more refined models of the impacts of anthropogenic climate change that have higher predictive power. 2. We thus continually monitored the body (operative) temperature of the intertidal mussel Mytilisepta virgata in both sun-exposed and shaded microhabitats and determined the seasonal variations of cardiac performance of field-acclimatized and laboratory-acclimated mussels from different microhabitats for calculating the thermal sensitivity, as indicated by the difference between the maximum ambient temperature and an individual's upper thermal limit (thermal safety margin, TSM), in each microhabitat and each month. 3. The mussels experienced divergent thermal stress, in average temperature, acute and chronic thermal stress and thermal predictivity among different microhabitats, and presented high spatial-temporal variations of cardiac function as results of seasonal acclimatization and inter-individual variations. Results of TSMs indicated that the thermal sensitivities of the mussels to high temperature were season- and microhabitat specific, and the mussels in the shaded microhabitats were predicted to survive the hottest summer temperatures; however, some individuals in the sun-exposed microhabitats experienced temperatures above their sublethal temperature. 4. With the large, high-resolution dataset of thermal environmental characteristics and the cardiac performances with high variations, we were able to integrate the effects of synchronized changes in microenvironmental temperatures and cardiac thermal responses and thereby characterize the physiological landscape of thermal sensitivity. The complex physiological landscape that exists in the intertidal zone must be taken into account when predicting the effects of changes in environmental temperature, such as those occurring with global climate change.