Biofouling on aquaculture mesh: disentangling seasonal and environmental effects with DNA metabarcoding

Biofouling presents ecological and economic challenges for marine industries, yet patterns of community development in relevant environments remain underexplored. In this study, we investigated seasonal (winter vs. summer) and spatial (sheltered vs. exposed) patterns of eukaryotic biofouling across six coastal sites in New Zealand. Using standardised mesh substrates and DNA metabarcoding with the 18S rRNA gene, we characterised over 10,000 amplicon sequence variants (ASVs) across 216 samples, revealing 541 species from 249 taxonomic classes. Exposed sites exhibited marked seasonal contrasts: winter communities were dominated by hydroids (e.g. Coryne eximia), whereas summer assemblages were rich in amphipods (e.g. Jassa slatteryi). Sheltered sites showed more stable biomass and diversity but greater site-level variability, especially in summer. Temperature and wind fetch were strongly associated with community variation, with larger seasonal fluctuations observed under high-exposure conditions. Notably, several dominant species were non-native, underscoring the importance of early detection and tailored antifouling strategies.