Mussel production as a nutrient mitigation tool for improving marine water quality

Longline mussel farming has been proposed as a tool to remove nutrients and counteract the negative effects of eutrophication in coastal waters. In this study, we use coupled 3D hydrodynamic and ecological modelling in combination with measurements from a full-scale mitigation farm to assess the environmental effects of mitigation cultures in Skive Fjord, Denmark, a shallow eutrophic estuary. The results show that mitigation cultures decrease chl a concentration and increase Secchi depth especially in the surroundings of the farms but also on a basin scale. Fecal production by the mussels increases sedimentation below the farms but reduces ambient sedimentation, resulting in a net decrease in sedimentation of organic material on a basin scale. Comparisons with nutrient load reduction scenarios indicate that nutrient removal by mitigation cultures have a higher short-term impact on water quality parameters (chl a, Secchi depth and sedimentation) than nutrient removal using land-based measures.