Beneath the surface: DNA metabarcoding reveals shifting biofouling patterns on marine artificial structures across season, depth, and substrate

Spatially and temporally varying environmental conditions, together with settlement substrate type, drive variation in marine biofouling communities and limit prediction of fouling pressure in marine systems. This study investigated biofouling community dynamics in relation to season, deployment length, water depth and settlement substrate using a replicated experimental design conducted over two four-month seasonal periods (summer and winter) to measure seasonal succession and monthly recruitment patterns. Two synthetic materials (Dyneema® mesh and UHMWPE-TPU composite fabric) were deployed at three depths (surface, 5 m, and 10 m). DNA metabarcoding of 432 samples using the 18S rRNA gene identified 10,214 amplicon sequence variants assigned to 245 taxonomic classes across the complete dataset, including 540 identified species. Season explained the largest share of variation in biomass, alpha and beta diversity, and community composition, whereas substrate and depth had smaller but significant effects, particularly for monthly recruitment communities. Winter assemblages were characterized by dense and persistent communities dominated by Hydrozoa, whereas summer communities showed rapid but more removable accumulation dominated by Oligohymenophorea and Malacostraca, likely reflecting seasonal differences in temperature, light availability, storm exposure, and larval supply. Depth effects were found in both seasons, with Caprella equilibra more abundant in deeper waters. Substrate effects showed lower biomass but higher relative abundances of Phyllopharyngea on composite fabric compared to mesh. Site-level variation was minimal compared with other factors. Temperature was influenced mainly by season, with only minor differences among depths. By contrast, light availability varied with both season and depth. Together, these findings show that biofouling dynamics are shaped by interacting environmental factors and substrate type, but that predictable patterns associated with season, depth, and substrate can still be identified. Effective antifouling and maintenance strategies should therefore account for these interacting factors to improve performance, reduce fouling pressure, and support more targeted management of submerged marine structures.