Analysis of Arabian Gulf biofouling communities using environmental DNA metabarcoding with COI

Ports and marinas are recognized as global hotspots for non-indigenous species (NIS), yet data from the Arabian Gulf, a region of strategic maritime and ecological importance, remain limited. Here, we provide one of the most spatially extensive assessments of biofouling communities along the Saudi Arabian Gulf coastline, surveying 12 sites across ~300 km using both DNA (COI-based) metabarcoding and image-based analyses. We characterized early-stage (settlement panels) and mature (pontoons and docks) assemblages, capturing a wide taxonomic spectrum, including native, cryptogenic, and non-indigenous taxa. Community composition was primarily structured at the site level, shaped by substrate type, orientation, and local environmental conditions, rather than by broader geographic location or environmental risk category. DNA metabarcoding of COI genes detected significantly more taxa, including 57 cryptogenic and NIS, many of which were undetectable by visual surveys. Industrial and commercial ports showed higher NIS richness and abundance than recreational marinas, indicating localized invasion risk. Despite the advantages of DNA-based methods, species-level identifications require cautious interpretation due to limited reference databases for the region. Our results emphasize the need for site-specific monitoring and integrated multi-method approaches, and they establish a critical baseline for marine biosecurity efforts in the underrepresented ROPME Sea Area.