The geography of marine larval dispersal: Coupling genetics with fine-scale physical oceanography

Efforts to understand the population dynamics of marine species with planktonic larvae have been stymied by the fact that the larvae recruiting to a location have little chance of originating from that site. Patterns of,larval movement and the spatial scale of dispersal are expected to be major forces regulating the dynamics of marine populations and communities. Unfortunately, the scale and predictability of larval dispersal and its regulation by physical circulation remains unknown due largely to the impossibility of measuring dispersal in open marine environments. Here we exploit strong genetic differentiation among marine mussel populations in southwest England to measure larval dispersal among adjoining genetic patches. This approach allows estimates of larval dispersal over relatively great distances. We combine these measurements with results from a high-resolution model of coastal circulation to test the hypothesis that larval dispersal is regulated by physical circulation. We show that larval dispersal typically occurs over distances of similar to30 km but in some cases was at least 64 km. The circulation model accurately predicted general patterns of larval transport between genetic regions, the scale of larval dispersal, and genetic isolation created by physical barriers to circulation. We demonstrate that physical circulation models and genetic measures of larval transport can be coupled to assess the geographic scale of larval dispersal in marine environments.