Low temperature exposure determines performance and thermal microhabitat use in an intertidal gastropod (Littorina scutulata) during the winter

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Small-scale spatial variation in temperature is an important attribute of many habitats, as spatial thermal refugia may allow organisms to avoid some negative consequences of thermal extremes. Although the ecological importance of thermal refugia in intertidal habitats is well-known in summer, the relative availability, effectiveness, and ecological relevance of thermally benign microhabitats in the winter is poorly understood. Here, we explored small-scale thermal variability on a temperate rocky coastline during winter, and the relevance of these thermal patterns to Littorina scutulata, a common intertidal gastropod. Sheltered microhabitats, including crevices, undersides of boulders, and areas beneath algal canopy, were all warmer than surrounding exposed areas during winter low tides. L. scutulata was able to recover relatively quickly from exposure to low temperatures down to -3°C, but performance costs began to accrue at lower temperatures. However, the presence of a refuge habitat buffered the negative effects of cold temperatures, and sheltered L. scutulata regained mobility more quickly than conspecifics on exposed surfaces. Further experiments demonstrated that L. scutulata were more frequently found in thermal refugia when previously exposed to low temperatures, but not when exposed to milder temperatures. Our results suggest that realistic low temperatures can impose important costs on intertidal species such as L. scutulata, but the availability of thermal refugia coupled with behavioural adaptations can allow species to reduce many such costs. Just as in summer, thermal refugia in winter may be important for the distribution and abundance of intertidal species and the diversity and function of coastal ecosystems.