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Aim: Population connectivity of benthic marine organisms depends strongly on planktonic larval dispersal and is controlled by geographic distance and oceanographic structure. We examine isolation by distance versus resistance to barriers (ocean current boundaries) against a background of post‐glacial habitat expansion in a small benthic fish of the Adriatic Sea. Location: Adriatic Sea, Eastern Mediterranean. Taxon: Tripterygion tripteronotum. Methods: We performed population genetic analyses using mitochondrial control region sequences of 550 individuals from 25 locations sampled along the Eastern Adriatic coast. Investigations of population structure included differentiation tests, cluster analyses and distance‐based redundancy analysis. We then ran Lagrangian simulations of passive larval drift to examine correlations among population structure, geographic distance and the Adriatic gyre system. To test for signatures of a post‐glacial range expansion, we modelled the demographic history of the populations and examined the geographic distribution of genetic diversity. Results: Genetic population structure corresponded to the Adriatic gyres without additional effect of geographic distance. Inference of northward‐biased gene flow between the northern and the Istrian gyre was consistent with simulated trajectories of passive drift, whereas the phylogeographic break coinciding with the boundary between the Central and the Northern Adriatic gyre was stronger than predicted by drift simulations. Genetic connectivity of populations within gyres was high. Genetic signatures of population expansion were consistent with a rapid post‐glacial recolonization of the northern Adriatic. Main conclusions: The combination of dense sampling and passive drift simulation allowed us to distinguish among effects of geographic distance, oceanographic features and palaeoenvironmental changes on current population structure. Comparisons between realized and potential connectivity illustrate the value of integrating different data sources to understand population structure and inform conservation planning. [ABSTRACT FROM AUTHOR]

Population histories depend on the interplay between exogeneous and endogeneous factors. In marine species, phylogeographic and demographic patterns are often shaped by sea level fluctuations, water currents and dispersal ability. Using mitochondrial control region sequences ( n = 120), we infer phylogeographic structure and historic population size changes of a common littoral fish species, the black-faced blenny Tripterygion delaisi ( Perciformes, Blennioidei, Tripterygiidae) from the north-eastern Adriatic Sea. We find that Adriatic T. delaisi are differentiated from conspecific populations in the remaining Mediterranean, but display little phylogeographic structure within the Adriatic basin. The pattern is consistent with passive dispersal of planktonic larvae along cyclonic currents within the Adriatic Sea, but limited active dispersal of adults. Demographic reconstructions are consistent with recent population expansion, probably triggered by rising sea levels after the last glacial maximum ( LGM). Placing the onset of population growth between the LGM and the warming of surface waters (18 000-13 000 years BP) and employing a novel expansion dating approach, we inferred a substitution rate of 2.61-3.61% per site per MY. Our study is one of only few existing investigations of the genetic structure of animals within the Adriatic basin and is the first to provide an estimate for mitochondrial control region substitution rates in blennioid fishes. [ABSTRACT FROM AUTHOR]