Assessing the effect of salmon aquaculture on fungal diversity in seawater and sediments through eDNA metabarcoding

Fungi have been found to play important roles in marine ecosystems, e.g., symbionts of plants and animals, and as decomposers of organic materials. The fungal communities, however, are often considered less studied and their functional and taxonomic diversity in aquatic environments remains poorly understood. Since the 1970s the Norwegian salmon industry developed from a small-scale industry to becoming the world’s leading producer of Atlantic salmon (Salmo salar L.). To investigate the impact of aquaculture on fungal diversity, fungal DNA was extracted and amplified from environmental samples collected at an active commercial scale aquaculture facility in Arctic Norway. In this study, environmental samples from water and sediment surrounding the aquaculture were collected and investigated for the determination of fungal community diversity and composition variance. Through 18S metabarcoding, a high-level fungal diversity was revealed by 4,554 Molecular Operational Taxonomic Units (MOTUs) that spanned nine phyla. Over a grid of 12 sampling points at increasing distance from the farm, all effected the fungal diversity, and combined with known physical factors (season), provided evidence that fungal community diversity and composition are highly influenced by seasonal variations. To distinguish the patterns of impact, alpha and beta diversity for each sampling point were analyzed. Analysis showed that the aquaculture only affected the alpha diversity within 250m from the farm in water samples. Although, alpha diversity suggested impact in water, no such observations were observed for sediments. The study also finds that the beta diversity indicated a higher spatial variation in fungal diversity in water samples compared to sediments. These findings support the hypothesis that the fungal diversity decreases with increased distance from the aquaculture cages for water samples but is rejected for sediment samples. The discoveries highlight the capability of 18S metabarcoding to assess the spatiotemporal trends of fungal community diversity and composition, encouraging the need for further biodiversity assessments