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Agent-based modeling and genetics reveal the Limfjorden as a well-connected system for mussel larvae

Ane Pastor*, Janus Larsen, Flemming Thorbjørn Hansen, Alexis Simon, Nicolas Bierne, Marie Maar

*Corresponding author:

ABSTRACT: Fishery of blue mussels constitutes a very important economic activity in Denmark, whereas mussel farming on long-lines or nets is a new, growing sector. Spawning from natural mussel beds takes place during early summer, and larvae are spread by the water currents before settling on the bottom or on spat collectors in the farms. In the present study, we coupled a 3D physical model system (FlexSem) with an agent-based model in order to examine the connectivity of this marine system in terms of mussel larval dispersal and settling potential. To address this question we (1) estimated the dispersal and connectivity between 17 areas in the Limfjorden, (2) identified the main donor and receiver areas of mussel larvae, and (3) identified possible dispersal barriers. The results show that the central narrow strait in the Limfjorden is the main donor area in all the studied years, and that the eastern areas adjacent to these are the main receiver areas. As we move towards the inner basins of the Limfjorden, the isolation increases and limited connectivity is observed. The results from the cluster analysis groups the Limfjorden into 3 to 5 clusters, but there is still some exchange of simulated larvae observed among these clusters. Analysis of molecular markers reveals no genetic differentiation between areas and supports the model results, indicating that despite distinguishable hydrographic boundaries, the mussel populations in the Limfjorden are well connected. This study demonstrates how connectivity modelling can be used to support site selection processes in aquaculture. KEY WORDS: Larval dispersal · Connectivity · Agent-based modeling · Mussel farms · Mytilus edulis · Limfjorden