| Summary: | The stock structure of edible crab (Cancer pagurus) and European lobster (Homarus gammarus) in the Irish Sea was investigated using eleven and twelve microsatellite markers, respectively. These shellfish species are of high economic value to the UK and Ireland and are being exploited with increasing intensity due to the decline of fin-fisheries. Population structure of H. gammarus was assessed by combining population genetic analysis of adults and biophysical modelling of larval dispersal, with particular emphasis on assessing recruitment patterns for the Lundy (South Wales) No-Take Zone (NTZ). Genetic structuring was statistically non-significant, compatible with recurrent spatial connectivity predicted by the larval dispersal modelling. The NTZ exhibited a statistically higher FIS and lower mean relatedness values which, in light of the predicted high proportion of allochthonous larval recruits, are attributed to increased variances in reproductive success linked to post-settlement processes. Likewise, microsatellite variation for C. pagurus supported a model of a single panmictic population within the Irish Sea. Integration of data collected throughout the Northeast Atlantic indicated high gene flow throughout the studied region but with some level of chaotic genetic patchiness likely due to sweepstakes recruitment episodes. As a comparison, the potential of Restriction-site Associated DNA sequencing (RADseq) as a future tool for population genetic analysis and fisheries management of C. pagurus was also investigated, with this being, to our knowledge, the first application of these methods to a crustacean. Seven RADseq libraries permitted genotyping of 566 polymorphic Single Nucleotide Polymorphisms (SNPs) among C. pagurus sampled throughout the Northeast Atlantic. Multiple marker-based neutrality tests revealed three consensus positive outlier SNPs. However, these were not significant in pairwise outlier tests and geographical patterns of allelic variation did not lend themselves to robust inference of environmental drivers. The neutral SNP data revealed a lack of wide scale geographic structure but more pronounced chaotic genetic patchiness than reported for microsatellites, indicative of greater sensitivity to neutral structuring. The implications of the findings for marine community ecology, fisheries management and NTZ design strategies are discussed.
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