Temperature or transport? Range limits in marine species mediated solely by flow

Clusters Of range boundaries in coastal marine species often occur at shoreline locations where major nearshore ocean currents collide. Observing that these currents are typically composed of waters with quite different physical characteristics, biologists have traditionally assumed that high local densities of marine range limits result primarily from the strong water property gradients (particularly in temperature) that arise at oceanographic discontinuities. However, this view may overlook the potential for ocean flows themselves to generate distributional pattern. Here we explore this possibility in more detail using an extension of a coupled population dispersal model developed previously for benthic marine species with dispersing larvae. Results suggest that simple, common flow fields often observed in association with biogeographic boundaries worldwide may have the potential to constrain a species' geographic range, even when suitable habitat outside that range is abundant. Model predictions suggest that these boundaries can function as one- or two-way barriers to range expansion and may be differentially permeable, with boundary leakiness depending on life-history characteristics and the degree of temporal variability in the nearshore flow field.