MIcrobial biodiversity of sediments under Atlantic salmon (Salmo salar)  aquaculture farms

Abstract

In recent years, the industry of salmon farming has grown significantly, and in the Faroe Islands it has become a major industry with an annual production of over 80,000 tons. However, the environmental impact on the surroundings and its biota, in specific the microorganisms, is mostly unknown. The aim of this study is to assess the impact of Atlantic salmon farming on benthic microbial communities in Sørvágsfjord in the Faroe Islands. With a kayak corer, 14 sediment samples were collected along a transect from right beneath
the salmon cages to a background reference site. Two sets of samples were collected. The first set was collected after a three month fallowing period just before the salmon were put into the cages and the second set was collected just before the salmon were harvested (the biomass at its highest). Each sample was divided into depth layers of surface, 3 cm depth and 10 cm depth. Samples were split into three replicates, and the microbial 16S rRNA (V4-V5) was sequenced
on an Illumina MiSeq. Shifts in microbial community composition were significant between low and high biomass and between depth layers. Microbial diversity increased with increasing distance from the cages and was at its highest during low salmon biomass. Predominant taxa at high impact sites were Clostridia, Spirochaetia, Bacteroidetes and Epsilonbacteraeota, and all showed an increase in abundance with salmon biomass. Most dominant taxa at all sites were Delta- and Gammaproteobacteria, where Gammaproteobacteria mostly dominated less impacted sites. Samples directly beneath the cages during high-salmon biomass had some indication of pollution, in specific an elevated abundance of Clostridia and Spirochaetaceae and the lowest overall richness. In contrast to the environmental assessment the results from this study show a clear impact on the microbial communities from the salmon aquaculture.
Concluding that microorganisms respond quickly to environmental changes, which underlines the importance of studying benthic microbial communities as a tool to assess the impact of salmon aquaculture activities on the surrounding environment.

Date of Award	23 Sept 2021
Original language	English
Awarding Institution	Aalborg University
Supervisor	Niels Madsen (Supervisor), Svein-Ole Mikalsen (Supervisor), Eyðfinn Magnussen (Supervisor) & Anni Djurhuus (Supervisor)