ermal threshold and sensitivity of the only symbiotic editerranean gorgonian Eunicella singularis by orphometric and genotypic analyses uils et sensibilités thermiques de la seule gorgone symbiotique de ́ diterranée Eunicella singularis par analyses mophométriques et notypiques xis

The only symbiotic Mediterranean gorgonian, Eunicella singularis, has faced several mortality events connected to abnormal high temperatures. Since thermotolerance data remain scarce, heat-induced necrosis was monitored in aquarium by morphometric analysis. Gorgonian tips were sampled at two sites: Medes (Spain) and Riou (France) Islands, and at two depths: –15 m and–35 m. Although coming from contrasting thermal regimes, seawater above 28 8C led to rapid and complete tissue necrosis for all four populations. However, at 27 8C, the time length leading to 50% tissue necrosis allowed us to classify samples within three classes of thermal sensitivity. Irrespectively of the depth, Medes specimens were either very sensitive or resistant, while Riou fragments presented a medium sensitivity. Microsatellite analysis revealed that host and symbiont were genetically differentiated between sites, but not between depths. Finally, these genetic differentiations were not directly correlated to a specific thermal sensitivity whose molecular bases remain to be discovered. 2013 Académie des sciences. Published by Elsevier Masson SAS. All rights reserved.