Abstract
The boundaries between oceanographic domains often function as dispersal barriers for many temperate marine species with a dispersive pelagic larval phase. Yelloweye rockfish (Sebastes ruberrimus, YR) are widely distributed across the northeastern Pacific Ocean, inhabiting coastal rocky reefs from the Aleutian Islands in Alaska through southern California. This species exhibits an extended pelagic larval duration and has the capacity for long distance larval transport. We assayed 2,862 YR individuals from 13 general areas in the northeast Pacific Ocean for allelic variation at nine microsatellite loci. Bayesian model-based clustering analyses grouped individuals from the Strait of Georgia (SG) into a distinct genetic cluster, while individuals from outer coastal water locations (OCLs) were partitioned equally across two genetic clusters, including the cluster associated with the SG fish. Pairwise FST values were consistently an order of magnitude higher for comparisons between the SG and OCLs than they were for all OCL-OCL comparisons (∼0.016 vs. ∼0.001). This same pattern was observed across two time points when individuals were binned into an “old” and “young” group according to birth year (old: ∼0.020 vs. 0.0003; young: ∼0.020 vs. ∼0.004). Additionally, mean allelic richness was markedly lower within the SG compared to the OCLs (8.00 vs. 10.54–11.77). These results indicate that the Strait of Georgia “deep-basin” estuary oceanographic domain acts as a dispersal barrier from the outer coastal waters via the Juan de Fuca Strait. Alternatively, selection against maladapted dispersers across this oceanographic transition may underlie the observed genetic differentiation between the Georgia basin and the outer coastal waters, and further work is needed to confirm the SG-OCL divide acts as a barrier to larval dispersal.
Highlights
Population replenishment for a large number of marine populations depends upon the input of exogenously derived individuals [1,2,3,4], which can occur via an extended pelagic larval phase [5,6]
While increasing the number of sample locations within the Strait of Georgia, as well as the number of temporal comparisons would bolster the robustness of the population structure we observed, similar results were found in a separate analysis conducted with a different molecular marker type, Amplified Fragment Length Polymorphisms [75] and with results for other rockfishes [45,48,51]
Our analyses support a population boundary between the inshore waters of the Strait of Georgia and the outer coastal waters that coincides with the transition between two oceanographic domains via the Juan de Fuca Strait
Summary
Population replenishment for a large number of marine populations depends upon the input of exogenously derived individuals [1,2,3,4], which can occur via an extended pelagic larval phase [5,6]. Oceanography is an important driver of population structure in temperate reef fishes, as ocean currents largely dictate larval trajectories, planktonic survival and delivery to settlement habitat [7,16]. There are a number of retention mechanisms that limit dispersal distances [18,19,20,21,22]. These include fronts associated with upwelling [23] or the intersection of independent current systems [24], gyres that form around seamounts or other complex bathymetric features [25,26,27], and eddies [28,29], including those formed by currents moving around rugged coastlines [30,31]. Genetic structure that occurs across oceanographic features suggests that these features may function as long-standing barriers to dispersal [37,38,39], influencing the spatial scale of ecological and evolutionary processes
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