Management of fishery species having a pelagic larval phase is plagued by poor estimates of their population connectivity. Meeting this challenge, I assessed variability in mtDNA COI and 7 microsatellite markers across 34 sites spanning the entire range of the subtidal gastropod Kelletia kelletii, an ecologically significant and rapidly emerging fishery species along western North America's coast that recently expanded its range north of Point Conception. Population genetic patterns were evaluated in relation to the geographic distribution of sampling sites, as well as in relation to a novel estimate of connectivity derived from simulations of virtual larvae in a realistic model of ocean currents.

Results/Conclusions

Spatial-genetic clustering indicates limited gene flow across biogeographic boundaries Punta Eugenia, Baja California, Mexico and Point Conception, California, USA, as well as isolation of western-most populations in the southern California bight. High genetic diversity in populations north of Point Conception coupled with spatial-genetic clustering suggests that K. Kelletia's expanded range was colonized by multiple sources from as far south as Baja California. Within K. Kelletia's historic range, significant genetic isolation-by-distance slopes estimate mean dispersal distance to be in the tens of kilometers, indicating low migration rates among non-proximate populations. When evaluated by region, isolation-by-distance was significant along the Baja California coastline and throughout the California Channel Islands, but not significant when evaluated across southern California bight populations, suggesting that in this region conventional methods based on Euclidean distance may be inadequate for explaining genetic differences among populations along the southern California mainland, or between populations along the mainland and those on the Channel Islands. Using a realistic simulated model of ocean currents we simulated dispersal trajectories of K. Kelletia virtual larvae, and found frequency of dispersal to not correlate with Euclidean distance between sampling sites. Explicit consideration of frequency of dispersal in lieu of Euclidean distance fundamentally changed our interpretation of the genetic data, revealing significant and previously undetected genetic structuring among populations along the mainland and across the Channel at small spatial scales germane to conservation and fisheries management.