Modelling mussel larval distribution in the Limfjord for optimal site selections of mussel farming

Mussel aquaculture in the Danish fjord Limfjorden has the largest potential in relation to production volume, economic potential and sustainability. Spawning of the blue mussel Mytilus edulis takes place in the natural mussel beds during spring. The resultant larvae are then spread by the water currents to other areas before settling on the bottom, or on the long-lines in the mussel farms. The farms should be located in areas with a high and stable year-to-year recruitment of mussel larvae and be climate ready, taking changes in future distributions of larvae into account. In the following study, we used a 3D ecosystem modelling tool to estimate the mussel larval distribution on fine spatial and temporal scales in a local set-up of the Limfjorden. We coupled a 3D physical Limfjord model with an agent based model (ABM) using the Flexsem system, where the larvae were defined by several biological parameters. Preliminary results show that there is a high proportion of larval self-recruitment in the system. This is the case in all areas except for Nissum Bredning and Hjarbæk Fjord. Kås Bredning seem to be the main donor area, and Skive Bredning the main receiver area. Connectivity results can be explained by the current circulation patterns in the area. The model provided maps of mussel larvae distribution and will be used for site-selection processes of mussel farming in the fjord. These results are of fundamental importance for the development of mussel farming as a measure to mitigate eutrophication.