Connectivity and gene flow are of great importance for the dynamics and persistence of populations. Understanding how dispersal and gene flow structure populations in the marine environment is crucial for the improvement of fisheries management and for the development of conservation strategies. In this study, we aimed to spatially unravel gene flow patterns of the striped red mullet Mullus surmuletus in the Mediterranean Sea using a spatial graph approach, combined with analyses of geographic patterns of genetic variation and a multi-generational approach to larval dispersal. Our results showed a low genetic structure and high level of admixture for M. surmuletus in the Mediterranean Sea, indicating high levels of gene flow. A spatial graph then allowed us to further untangle intra-population genetic structure by providing a spatially explicit representation of the genetic connectivity network. Topology revealed a centralized network, and quantitative analyses revealed Mediterranean islands as important stepping-stones in the network, suggesting that islands can be important corridors for gene flow between continental populations. Stepping-stone larval dispersal partially explained genetic connectivity (P = 0.004, Mantel r = 0.144), highlighting the importance of considering multiple generations and different time scales when relaying larval and genetic connectivity.
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