Holobiont diversity in heterogeneous and anthropized marine environments
Résumé
Marine biodiversity is impacted by local and global anthropic pressures. In this context, it is crucial to better understand the adaptative abilities of ecologically key species facing heterogeneous and changing environments. We chose the yellow gorgonian, Eunicella cavolini, as a model species : this octocoral is an ecologically important species of benthic Mediterranean ecosystems which can be found in contrasted thermal conditions (different depths and regions) and can colonize sites near pollution sources in coastal areas. As other Mediterranean gorgonians, Eunicella cavolini is recurrently impacted by mass mortality events linked to marine heat waves. We studied the genetic variation of the gorgonian holobiont along depth (20-40 m) and pollution (a major sewage outfall) gradients, with two sampling seasons in each case. Our project took place at a local scale near the city of Marseille, in the area of the Calanques National Park. We considered different components of the holobiont to study their changes across diverse environmental conditions and the interactions between these components. Regarding microbial diversity we analysed the overall composition and structure of communities of viruses, bacteria and micro-eukaryotes associated with gorgonians from eight study sites. At the host level, we characterized the demographic structures of the studied population. We also analysed the genomic diversity of the gorgonian to precise species limits and to study the differentiation and connectivity among sites and environments. The findings will allow to address questions relating to holobiont structuring factors and to test for correlations between host diversity and environmental conditions or microbial diversity. We will present here the results obtained for the diversity of the host genome, inferred from RAD-sequencing, and of microbial communities, analysed with 16S metabarcoding.