Understanding spatial and temporal variability in connectivity patterns between marine populations, in order to develop efficient spatial management strategies, is still a challenge. Distinctive geochemical signatures on calcified structures according to water characteristics are increasingly being implemented as a natural tagging technique which allows a direct measurement of connectivity. We used the mussel Mytilus galloprovincialis as a model-species to investigate the spatial-temporal variability of the connectivity patterns among two Portuguese Marine Protected Areas (Berlengas and Arrábida MPAs) along the central Portuguese west coast. By investigating the microchemistry of bivalve larval shells (using laser ablation inductively coupled plasma mass spectrometry-LA-ICPMS) during the peaks of the reproductive season of mussels (Spring and Autumn) we generated a reference map of location-specific chemical signatures for each season. These atlases were then employed to back trace natal origins of newly settled mussels and build connectivity matrices between populations. Our results show high seasonal variability in the signals for each region, which reflects the variability of the water characteristics over the year. Nonetheless, both Spring and Autumn signals allow us to identify 3 regions with distinctive signatures: Estremadura (including Berlengas), Baía de Cascais and Arrábida. Linear discriminant analyses allowed for a high reclassification success (60%-83% and 71-82% of jackknifed cross-validated cases correctly classified in June and September respectively) based on 9 of the 16 trace-elements analyzed. The connectivity matrices allowed the identification of different pathways for mussel larvae depending on season, showing a southward prevailing dispersion pattern during spring and a reversed dispersion pattern during autumn. The seasonal variation of the connectivity patterns seems to be related to the prevalence and intensity of upwelling/downwelling episodes during each season. Since the upwelling regime is seasonal, phenological changes on reproduction might also alter the connectivity patterns between these two MPAs, and compromise the persistence of certain subpopulations

Symposium on the Human Impacts on Marine Functional Connectivity, 22–25 May 2023, Sesimbra, Portugal

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