Gene flow in macroalgal populations can be strongly influenced by spore or
gamete dispersal. This, in turn, is influenced by a convolution of the effects
of current flow and specific plant reproductive strategies. Although several
studies have demonstrated genetic variability in macroalgal populations
over a wide range of spatial scales, the associated current data have generally
been poorly resolved spatially and temporally. In this study, we used a combination of population genetic analyses and high-resolution hydrodynamic
modelling to investigate potential connectivity between populations of the
kelp Laminaria digitata in the Strangford Narrows, a narrow channel characterized
by strong currents linking the large semi-enclosed sea lough, Strangford
Lough, to the Irish Sea. Levels of genetic structuring based on six microsatellite
markers were very low, indicating high levels of gene flow and a pattern of isolation-by-distance, where populations are more likely to exchange migrants
with geographically proximal populations, but with occasional long-distance
dispersal. This was confirmed by the particle tracking model, which showed
that, while the majority of spores settle near the release site, there is potential
for dispersal over several kilometres. This combined population genetic and
modelling approach suggests that the complex hydrodynamic environment
at the entrance to Strangford Lough can facilitate dispersal on a scale exceeding
that proposed for L. digitata in particular, and the majority of macroalgae
in general. The study demonstrates the potential of integrated physical–
biological approaches for the prediction of ecological changes resulting from
factors such as anthropogenically induced coastal zone changes.