Discussion
Improving predictions for how species and communities will be affected by climate change and extreme events is an urgent challenge. Here we examined how populations of the functionally important seagrassPosidonia oceanica could be affected by heat stress, by conducting a translocation experiment across its range. Cool-edge, central and warm-edge populations displayed clear differences in thermal performance when grown under common conditions, but patterns contrasted with a priori expectations based on their thermal geography. Cool-edge populations performed equally well to warm-edge populations under common conditions and significantly better than central populations in terms of growth rates and survivorship. The strong performance of cool-edge populations was remarkable given they experienced thermal anomalies of >5ºC above long term summer maxima, compared to 1.5ºC for central populations and <1ºC for warm-edge populations. Moreover, cool-edge transplants suffered and subsequently recovered from severe overgrazing at the warmest site that removed >75% of aboveground biomass, highlighting remarkable resilience of cool-edge populations to combined effects of thermal stress and herbivory – two pervasive impacts of climate change in marine ecosystems.