Rethinking climate change sensitivity: Drivers of spatial variation in thermal safety margins

Scott Bennett (1,2,3) , Thomas Wernberg (1), Francois Dufois (4), Nuria Marba (3), Teresa Alcoverro (5), Bijo Arackal- Joy (1), Thibaut de Bettignies (1), Alexandra Campbell (6,7), Carlos Duarte (8), Dorte Krause-Jensen (9)

1 UWA Oceans Institute (M470) and School of Plant Biology, University of Western Australia, Crawley 6009 WA, Australia

2 Department of Environment and Agriculture, Curtin University, Bentley, WA 6102, Australia

3 Institut Mediterrani d’Estudis Avançats/Department of Global Change Research, CSIC, Mallorca, Spain

4 Centre for Environment and Life Sciences, CSIRO Marine and Atmospheric Research, Floreat, Western Australia, 6014

5 Centre d’Estudis Avançats de Blanes, CSIC, Girona, Spain

6 Evolution and Ecology Research Centre; Centre for Marine Bio-Innovation, School of Biological, Earth and Environmental Sciences, University of New South Wales, Sydney, 2052, Australia

7 Sydney Institute of Marine Sciences, Chowder Bay, NSW, 2088, Australia

8 Red Sea Research Centre, Division of Biological and Environmental Sciences and Engineering, King Abdullah University of Science and Technology, Thuwal, Saudi Arabia

9 Department of Bioscience, Århus University, Denmark

Thermal safety margins describe the buffer between an organism’s thermal-tolerance limit and the maximum temperatures it experiences in its environment. A critical question for climate change science is whether spatial, broad taxonomic or trait based generalities determine the size of thermal safety margins. Answers would enable a more accurate identification of regions and populations at risk of climate change impacts. For instance, if a population living in a region of rapid warming thrives in conditions beyond the projected level of warming (i.e. large thermal safety margin) then the relative vulnerability that population may be low. In contrast, if a population living within a region of low rates of warming lives on the cusp of their thermal thresholds (i.e. small thermal safety margin) then even small changes to the climate could have catastrophic impacts. Using examples from a severe marine heatwave, a broad scale translocation experiment of a range contracting species and global oceanographic modelling of climate variability, we examine how thermal safety margins can vary throughout species’ geographical ranges and discuss how local and regional scale climatic variation can influence the sensitivity of organisms to warming.  Our findings highlight the importance of integrating intra-specific variation in thermal tolerance limits with the local climatological context of an area to more accurately understand spatial variability in climate change sensitivity in coastal marine ecosystems.