- Understanding connectivity of marine organisms is necessary for determining the appropriate scale of conservation and management strategies. For species that inhabit both the coastal ocean and partially enclosed water bodies (i.e., estuaries or fjords), this information is even more critical since estuaries and fjords are often characterized by hydrological complexities which can limit dispersal potential and promote population subdivision. In this study, genetic connectivity of Dungeness crab Cancer magister in Puget Sound and coastal Washington, USA, was examined to test the hypothesis of genetic structure in partially enclosed versus open environments. Dungeness crab that were sampled at five sites in Puget Sound in 2015 and three sites in coastal Washington in 2014 were genotyped at ten microsatellite loci. We observed similar levels of heterozygosity and allelic richness within Puget Sound and coastal Washington. Pairwise F ST estimates indicated that Hood Canal was significantly differentiated from other Puget Sound sites, except Nisqually, suggesting larval retention within the Hood Canal basin. No evidence for significant genetic differentiation was found among the four remaining Puget Sound sites or among the three coastal sites. Analysis of molecular variance indicated that, in aggregate, Puget Sound sites significantly differed from coastal sites. On a site by site basis, we found evidence for significant differentiation between three sites in Puget Sound and coastal Washington. Based upon the observed patterns of genetic differentiation, our findings did not support our hypothesis of restricted genetic connectivity within Puget Sound, with the exception of Hood Canal. However, our results demonstrate that there is stronger genetic connectivity within Puget Sound and coastal Washington than between these two areas.