Spatial and temporal variability of biofouling communities during early development in three French harbors of the...

Biofouling, the colonization of submerged surfaces by marine organisms, causes major economic losses in maritime activities. Although non-biocidal surface coatings are promoted as environmentally friendly antifouling solutions, the respective roles of surface properties and environmental conditions in shaping biofouling stages remain unclear. We hypothesized that coating surface properties primarily control early biofilm formation, whereas local environmental conditions govern subsequent macrofouling development. To test this hypothesis, we studied biofouling on two non-biocidal coatings - an anticorrosion epoxy and a fluoropolymer foul-release coating (FRC) - immersed under static conditions in three French harbors along the English Channel during the spring bloom. Early biofilm formation was assessed after 2 weeks in April, May, and June 2023 using chlorophyll a and the carbohydrate/protein ratio of extracellular polymeric substances (EPS). Macrofouling development over 3 months was evaluated through biomass, surface coverage rate, taxonomic composition, and microorganism abundances. Metagenomic analyses complemented the visual observations in Cherbourg during April and May 2023. The FRC showed a higher EPS carbohydrate/protein ratio, indicating greater resistance to initial microbial colonization, but exhibited significantly lower macrofouling intensity than the epoxy. This decoupling supports the hypothesis that surface properties and settlement processes operate at different spatial and temporal scales. Spatial variability in biofouling patterns may largely be associated with differences in nutrient availability and anthropogenic pressure. These findings demonstrate that early biofilm metrics alone cannot predict long-term fouling and highlight that antifouling performance depends on both material properties and environmental context. Integrating surface physicochemistry with site-specific ecological drivers can improve both coating design and antifouling evaluation strategies.