Diversity of gorgonian-associated bacterial communities in Northwestern Mediterranean Sea
Résumé
Associations between marine invertebrates and microbial communities are increasingly studied as it becomes apparent that bacteria can have a major role in host health and disease. In Northwestern Mediterranean Sea, recurrent mass mortalities have been observed affecting benthic macroinvertebrate species during anomalous high-temperature conditions in summer. Among cnidarians, the gorgonians were the most affected organisms. We previously reported the involvment of a thermodependent Vibrio in disease and mortality of the red seafan Paramuricea clavata, indicating a role of bacterial-hots interactions in gorgonian health status. To improve our understanding of gorgonian-bacteria relationships, microbial communities of four sympatric species, Paramuricea clavata, Corallium rubrum, Eunicella cavolinii and Eunicella singularis, were analyzed. As a first step, we aimed to establish a baseline for composition and dynamics of the bacterial assemblages associated with P. clavata in different locations. T-RFLP profiles were highly similar between three populations separated by hundreds of kilometers. No particular seasonal pattern was observed, but a deep and reversible shift in bacterial composition occurred in summer 2007. Except for this particular summer, all samples were dominated by a Gammaproteobacteria related to the Hahellaceae family. The associated communities in C. rubrum, E. cavolinii and E. singularis also harboured Hahellaceae members sharing highly related 16S rDNA sequences in each studied host. In the context of recurrent gorgonian mass mortalities in Mediterranean, the understanding of bacterial communities structure will be helpful to monitor the effects of thermal anomalies on these assemblages, and to assess their potential role in gorgonian health and resilience.