Thermal Performance of Seaweeds and Seagrasses Across a Regional Climate Gradient

Comparative patterns in thermal performance between populations have fundamental implications for a species sensitivity to warming and extreme events. Despite this, within-species variation is seldom measured. Here we compare both between-species, two of seagrass ( Posidonia oceanica Cymodocea nodosa ) seaweed Padina pavonica Cystoseira compressa across the Mediterranean Sea. Experimental from four locations representing 75 99% each distribution 6°C gradient summer temperatures, were exposed 10 temperature treatments 15 36°C. displayed greatest variability species, with optimal temperatures differing by over 10°C within same location. Within-species differences also important P. which large safety margins cool warm-edge small central populations. Our findings suggest seagrasses seaweeds retain deep “pre-Mediterranean” evolutionary legacies, suggesting marked benthic marine communities.