Realised thermal anomalies
The western Mediterranean Sea experienced marine heatwave conditions during 2018 summer, coinciding with the translocation experiment. Maximum daily cool-edge temperatures were 24.9 ºC, 1.3 ºC above long term summer maximum (averaged 1981-2019). Maximum daily temperatures in central sites were 29.1ºC, also 1.3 ºC above long term summer maximum and the second highest temperature on record. Maximum daily temperatures at P. oceanica’s warm-edge in the eastern Mediterranean were more typical at 29.3 ºC and 0.18 ºC above long term maximum.
As a result of the marine heatwave in the western Mediterranean, thermal anomalies experienced by cool-edge and central transplants were similar in central and warm-edge locations. The highest anomalies were experienced by cool-centre and cool-warm fragments, which experienced maximum anomalies of 5.4 ºC and 5.7 ºC above long-term maximum temperatures in the cool-edge, respectively. Positive thermal stress anomalies lasted for 130 days for cool-warm fragments and 102 days for cool-centre fragments over the course of the experiment (Fig. 2, Table S1). Centre-warm and centre-centre fragments experienced maximum anomalies of 1.53 ºC and 1.3 ºC, respectively for a duration of 37 and 33 days above long-term summer maxima in P. oceanica’s range centre. Warm-warm transplants experienced equally high temperatures to cool-warm and centre-warm transplants, but the smallest relative anomaly (0.18 ºC for 2 days) above long-term summer maxima. The coolest daily temperatures recorded throughout the course of the experiment ranged from 10.5 ºC in the cool-edge, 13.9 ºC in the centre and 16.2 ºC in the warm-edge.