Wandering mussels: using natural tags to identify connectivity patterns among Marine Protected Areas

Knowledge of connectivity pathways in the marine environment is crucial for understanding the spatial structure of populations and for developing appropriate monitoring and management strategies. Here, we used the mussel Mytilus galloprovincialis as a model species to investigate connectivity patterns within the Berlengas and Arrábida Marine Protected Areas (MPAs) along the central Portuguese west coast. We generated an atlas of location-specific environmental markers based on the microchemistry of bivalve larval shells (using laser ablation inductively coupled plasma mass spectrometry). This atlas was then employed to trace the natal origins of newly settled mussels and generate connectivity matrices among populations. Our results reflected 3 distinctive chemical signatures in larval shells, corresponding to 3 regions: Estremadura, Cascais and Arrábida. Linear discriminant analyses allowed for a high reclassification success (average of 79.5% of jackknifed cross-validated cases correctly assigned) based on 8 of the 16 trace elements analyzed (B, P, Co, Cu, Zn, Ce, Pb and U). The population connectivity matrix identified different dispersal pathways for mussel larvae, in particular a predominantly northward dispersion pattern in July 2013. This pattern was consistent with simultaneous environmental physical data, which confirmed an extended period of wind reversal and upwelling relaxation. The Arrábida MPA was an important source population for the other 2 regions and showed high rates of self-recruitment but limited connectivity to the Berlengas MPA. These direct measures of demographic connectivity can be a powerful tool to inform policymakers on the conservation and management of ecologically coherent networks of protected areas in coastal marine ecosystems.