Seascape drivers of Macrocystis pyrifera population genetic structure in the northeast Pacific

At small spatial and temporal scales, genetic differentiation is largely controlled by constraints on gene flow, while genetic diversity across a species ’ distribution is shaped on longer temporal and spatial scales. We assess the hypothesis that oceano-graphic transport and other seascape features explain different scales of genetic struc-ture of giant kelp, Macrocystis pyrifera. We followed a hierarchical approach to perform a microsatellite-based analysis of genetic differentiation in Macrocystis across its distribution in the northeast Pacific. We used seascape genetic approaches to iden-tify large-scale biogeographic population clusters and investigate whether they could be explained by oceanographic transport and other environmental drivers. We then modelled population genetic differentiation within clusters as a function of oceano-graphic transport and other environmental factors. Five geographic clusters were iden-tified: Alaska/Canada, central California, continental Santa Barbara, California Channel Islands and mainland southern California/Baja California peninsula. The strongest break occurred between central and southern California, with mainland Santa Barbar