Population genomics reveals a single semi-continuous population of a commercially exploited marine gastropod

Buccinum undatum is a commercially important marine gastropod with limited dispersal capabilities. Previous genetic studies utilising microsatellites and Double-digest Restriction-site Associated DNA sequencing (ddRADseq) provided evidence that B. undatum exhibits fine-scale genetic structure. Using ddRADseq, 128 individuals from the southern North Sea, English Channel, and the Irish Sea were genotyped using 7015 filtered single nucleotide polymorphisms (SNPs), 19 of which were identified as being under putative selection. Multiple genetic clustering methods – Discriminant analysis of principal components, Principal component analysis, and Sparse non-negative matrix factorisation,– were used to investigate population structure. Spatially explicit genetic structure was investigated using an Estimated Effective Migration Surface analysis and a Mantel correlogram. A single genetic population was found using neutral SNPs, with weak within-population structuring. Global FST was low (0.0046, p < 0.001), and pairwise FST estimates between sampling locations were between 0.0004 and 0.0224. There was a significant trend of isolation-by-distance across all sampling locations (r = 0.743, p < 0.001). Positive spatial autocorrelation indicated whelks located ≤ 50 km of one another were significantly more related than by chance (r = 0.12, p = 0.003), further emphasising the low dispersal capabilities of B. undatum. Finally, two barriers of lower-than-average dispersal were discovered; the Thames estuary and across the English Channel. Management implications are discussed for the sustainability of whelks from inshore fisheries.