As aquaculture production continues to increase, there has followed increasing concerns on the environmental impact from aquaculture. Blue mussels grown in a co-culture with fish aquaculture has been recommended to extract particulate waste from fish production. It is however, debated if significant mitigation can be obtained by direct waste assimilation, as studies have shown minimal mitigation by this method. Mussels can instead be used on a regional ecosystem scale, by controlling phytoplankton biomass, to avoid nutrient over-enrichment of the waters and eutrophication. The aim of this study was to evaluate how many nutrients can be harvested in blue mussel biomass in Faroese conditions, compared to what is emitted from a commercial Atlantic salmon farm. The aim is to fix nutrients into mussel biomass, and when the biomass is harvested, the nutrients are removed from the environment. A mussel growth experiment in Sørvágsfjørður, Faroe Islands and production data from a commercial salmon farm were used for this. The study showed that the salmon farm released 40 ton of dissolved inorganic nitrogen during summer, which could possibly increase phytoplankton biomass. Harvesting mussels containing 40 ton of nitrogen would require a biomass harvest of 2920 ton of mussel. The area needed to grow this biomass depends highly on the blue mussel density on the lines and the blue mussel farming strategy. Mussel spat settlement, density and growth varies greatly in different countries and regions, which is important for the nutrient harvest potential of an area.
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