Bimodal distribution of seafloor microbiota diversity and function are associated with marine aquaculture.

The aim of the current work was to investigate the impact of marine aquaculture on seafloor biogeochemistry and diversity from pristine environments in the northern part of Norway. Our analytical approach included analyses of 182 samples from 16 aquaculture sites using 16S and 18S rRNA, shotgun analyses, visual examination of macro-organisms, in addition to chemical measurements. We observed a clear bimodal distribution of the prokaryote composition and richness, determined by analyses of 16S rRNA gene operational taxonomic units (OTUs). The high OTU richness cluster was associated with non-perturbed environments and farness from the aquaculture sites, while the low OTU richness cluster was associated with perturbed environments and proximity to the aquaculture sites. Similar patterns were also observed for eukaryotes using 18S rRNA gene analyses and visual examination, but without a bimodal distribution of OTU richness. Shotgun sequencing showed the archaeum Nitrosopumilus as dominant for the high OTU richness cluster, and the epsilon protobacterium Sulfurovum as dominant for the low OTU richness cluster. Metabolic reconstruction of Nitrosopumilus indicates nitrification as the main metabolic pathway. Sulfurovum, on the other hand, was associated with sulfur oxidation and denitrification. Changes in nitrogen and sulfur metabolism is proposed as a potential explanation for the difference between the high and low OTU richness clusters. In conclusion, these findings suggest that pollution from elevated loads of organic waste drives the microbiota towards a complete alteration of respiratory routes and species composition, in addition to a collapse in prokaryote OTU richness.

Simulating particle organic matter dispersal beneath Atlantic salmon fish farms using different resuspension approaches.

An accurate representation of the particle organic matter (POM) footprint is necessary in order to effectively predict impacts upon benthic communities and the risk of excessive organic enrichment beneath aquaculture sea-cages. Consequently, bottom-related processes such as particle resuspension must be adequately parametrized and evaluated in the available numerical models. We implemented two approaches to model POM resuspension in a Lagrangian particle tracking model and compared their influence on footprint extension and gradients of depositional flux against a no-resuspension scenario. We performed simulations in both exposed and protected aquaculture locations, and at different stages of the Atlantic Salmon (Salmo salar) production cycle in Norway. Our results indicate that the use of sediment-dependent thresholds for resuspension has the potential to regulate the high levels of erosion produced when selecting a low critical value in constant-threshold approaches, particularly in dynamic environments with mixed sediment types.

Accurate assessment of the impact of salmon farming on benthic sediment enrichment using foraminiferal metabarcoding.

Assessing the environmental impact of salmon farms on benthic systems is traditionally undertaken using biotic indices derived from microscopic analyses of macrobenthic infaunal (MI) communities. In this study, we tested the applicability of using foraminiferal-specific high-throughput sequencing (HTS) metabarcoding for monitoring these habitats. Sediment samples and physico-chemical data were collected along an enrichment gradient radiating out from three Chinook salmon (Oncorhynchus tshawytscha) farms in New Zealand. HTS of environmental DNA and RNA (eDNA/eRNA) resulted in 1,875,300 sequences that clustered into 349 Operational Taxonomic Units. Strong correlations were observed among various biotic indices calculated from MI data and normalized fourth-root transformed HTS data. Correlations were stronger using eRNA compared to eDNA data. Quantile regression spline analyses identified 12 key foraminiferal taxa that have potential to be used as bioindicator species. This study demonstrates the huge potential for using this method for biomonitoring of fish-farming and other marine industrial activities.