Does thermal history influence the tolerance of temperate gorgonians to future warming?

To date, several studies have provided evidence that thermal stress affects the growth, survival and physiology of tropical and temperate macroinvertebrate species. However, few studies have focused on subtidal temperate species and the potential differential thermal tolerances of populations dwelling under contrasting temperature conditions. To assess the role that environmental history has on the response of the temperate gorgonian Eunicella singularis to thermal stress, we compared populations dwelling in the coldest and warmest areas of the NW Mediterranean Sea. Our results show that E. singularis populations from both areas exhibited a high resistance to thermal stress; however, populations from warmer areas had an increased tolerance to thermal stress. Specifically, the upper thermal limits found for cold and warm populations were 28 and 29 °C, respectively. The higher resistance of E. singularis colonies to thermal stress found in this study compared to the field temperature conditions during recent mass mortality events highlights that performing further thermotolerance experiments under contrasting levels of feeding is necessary to fully assess the tolerance thresholds displayed by both study populations. To our knowledge, this study provides the first evidence for the role of thermal history in shaping the thermotolerance responses of Mediterranean marine invertebrates dwelling under contrasting temperature environments.