Shear stress controls prokaryotic and eukaryotic biofilm communities together with EPS and metabolomic expression in a semi-controlled coastal environment in the NW Mediterranean Sea.

While waves, swells and currents are important drivers of the ocean, their specific influence on the biocolonization of marine surfaces has been little studied. The aim of this study was to determine how hydrodynamics influence the dynamics of microbial communities, metabolic production, macrofoulers and the associated vagile fauna. Using a field device simulating a shear stress gradient, a multi-scale characterization of attached communities (metabarcoding, LC-MS, biochemical tests, microscopy) was carried out for one month each season in Toulon Bay (northwestern Mediterranean). Shear stress appeared to be the primary factor influencing biomass, EPS production and community structure and composition. Especially, the transition from static to dynamic conditions, characterized by varying shear stress intensities, had a more pronounced effect on prokaryotic and eukaryotic beta-diversity than changes in shear stress intensity or seasonal physico-chemical parameters. In static samples, mobile microbe feeders such as arthropods and nematodes were predominant, whereas shear stress favored the colonization of sessile organisms and heterotrophic protists using the protective structure of biofilms for growth. The increase in shear stress resulted in a decrease in biomass but an overproduction of EPS, specifically exopolysaccharides, suggesting an adaptive response to withstand shear forces. Metabolite analysis highlighted the influence of shear stress on community dynamics. Specific metabolites associated with static conditions correlated positively with certain bacterial and algal groups, indirectly indicating reduced grazer control with increasing shear stress.