Effects of salmon farming on the benthic ecosystem of coastal shallow- and deep-water sites: towards a DNA-based environmental impact assessment

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Aquaculture is among the fastest growing food production sectors worldwide, with Atlantic salmon (Salmo salar) being among the most important marine aquaculture species. The rapid annual growth of this industry has yielded in significant socio-economic benefits but is accompanied by increasing environmental impact. In the first funding period of DFG project (sign removed) I could show that DNA metabarcoding of microbial benthic communities in combination with supervised machine learning (SML) is a very powerful method to (a) assess stress factors affecting benthic coastal ecosystems through aquaculture and (b) to quantify the environmental quality of coastal ecosystems under the influence of salmon farming. The obtained results suggested that this technology may in the future replace the much more expensive, lengthy, error-prone and tedious traditional biomonitoring based on the microscopic identification of benthic macroinvertebrates as bioindicators. However, project (sign removed) has also shown what crucial basic ecological knowledge about the impact of aquaculture stressors on benthic coastal ecosystems is still missing at this stage. The aim of the proposed continuation project is to fill this knowledge gap to the extent that the new technology can be implemented in routine environmental monitoring programmes. Specifically, the proposed project aims to investigate the spatial and temporal response of benthic microbial communities to different levels of stress exerted on coastal ecosystems by salmon farming. The proposed follow-up project should clarify which changes in benthic microbial communities are due to natural seasonal succession patterns and which are specifically caused by aquaculture stressors. Results from (sign removed) suggest that in shallower coastal waters natural seasonal influences may be a significantly stronger co-factor for structuring benthic communities under aquaculture stress than in deep coastal waters. The expected findings from this basic ecological research are of high relevance for the identification of specific DNA bioindicators in shallow- and deep-water aquaculture sites worldwide. Therefore, comparative studies will be carried out in both coastal systems. In a subsequent DFG knowledge transfer project, these new findings could then be tested with the aim of implementing the DNA metabarcoding/SML technology in official regulations for the ecological monitoring of coastal waters under the influence of aquaculture. Such a scientific concept and methodological approach will be widely applicable, including environmental impact assessments of offshore drilling, seabed mining, offshore wind farms, bottom trawling and various other types of industrial and recreational activities in coastal waters.