Nine sampling sites (SN1–SN9) were equally distributed along the SN transect, approximately one at each 150 km segments (Fig. 1A–B). At each sampling site along the SN transect, individual thalli were collected at three sub-sites, one central sub-site and two sub-sites about 2 km away (in opposite directions) from the central sub-site, for a maximal distance of 4 km from the two most distant sub-sites