Disentangling spatial variation in climate change impacts is a pressing challenge. Here we compared the performance of Posidonia oceanica seagrass populations to temperature, throughout a year-long translocation experiment across 2800 km in the Mediterranean Sea. Transplants in central and warm-edge locations experienced temperatures >29 ºC during summer, representing thermal anomalies >5ºC above long-term maxima for cool-edge populations, 1.5ºC for central and <1ºC for warm-edge populations. At the onset of the experiment, a highly selective herbivory event removed 75% of cool-to-warm transplant biomass but left adjacent central and warm-edge treatments intact. Despite big differences in thermal stress and acute herbivory, cool-edge populations recovered and matched warm-edge populations across all performance metrics. Central populations displayed significantly lower growth and survivorship in response to thermal stress. Our findings reveal that intraspecific variation in thermal performance does not necessarily reflect thermal geography and suggest greater resilience to warming for Posidonia oceanica than previously recognised.