PhD thesis abstract:




       Global climate change leads significant reactions on marine ecosystems which, when dealing with sessile species, can drive to episodes of mass mortalities. In the north-western Mediterranean Sea, recent events of mortalities severely impacted gorgonian communities, threatening their survival, but also all the associated biodiversity. The implementation of strategies of preservations requires preliminary acquisitions of the knowledge at ecological, evolutionary, physiological, biochemical, genomic and genetics levels. In this ambitious framework, these doctoral studies aimed to better define the answers induced by thermal stress of two Mediterranean symbiotic Cnidarians: the white gorgonian Eunicella singularis and the sea anemone Anemonia viridis.

         A first part of the works was carried out on two populations of the white gorgonian, associated with their photosynthetic symbionts (zooxanthelles), collected at two geographical zones with contrasted thermal profiles. This study allowed us to identify the superior limits of thermal resistance of the populations and to estimate the possible links between the genetic varieties of the hosts and the symbionts, and their thermal resistance.

          Complementary studies then allowed identifying, on this symbiotic gorgonian, early molecular indicators induced by a hyperthermia, implying the global antioxidant defenses capacities and the degree of protein ubiquitination.

         Finally, our studies led on the sea anemone allowed to deepen our knowledge developed on this model concerning the antioxidant enzymes and in particular the glutathione peroxidases (GPx). The measures of the GPx activities in the different holobiont compartments did not reveal major modifications during the stress, but the appearance of one activity band induced by the hyperthermia could represent a new potential marker of stress.


Key-words: Global warming; Symbiotic Cnidarians; Mediterranean gorgonians; Thermotolerance; Biomarkers; Oxidative stress.