Realized dispersal patterns in the ocean and the consequences for marine reserves

Understanding the scale of connectedness in marine populations is critical to designing effective conservation and management policies. On large spatial scales, geographic patterns of genetic structure may reflect connectivity among populations. To examine large-scale patterns of connectivity in marine populations, I investigate geographic patterns of genetic structure in coastal marine species with contrasting life histories. The results reveal concordant regions of limited connectivity for species with similar life histories, and suggest that genetic structure in species that are dispersed in ocean currents can provide clues to contemporary oceanographic connectivity. On local and regional scales, connectivity by larval dispersal provides the potential for one of the most important proposed benefits of marine reserves -- the ability for highly productive populations in reserves to enhance nearby fished sites through the export of larvae. I conduct a quantitative analysis of larval export from replicated reserve sites for a harvested intertidal mussel in South Africa. I use the spatial patterns of recruitment with increasing distance from the reserves to determine whether larval export is occurring, and over what scales. Results suggest that larval export from the reserves enhances recruitment to fished areas within several kilometers. In addition, I introduce and employ a method for using patterns of production and recruitment near reserves to estimate the distribution of larval dispersal scales in the target species, knowledge that is essential to understanding ecological and evolutionary processes as well as informing management decisions. Finally, I combine a review of existing empirical evidence for export with a theoretical model to predict, measure and evaluate benefits to fisheries through larval export. Both theoretical and empirical results suggest that in most systems, benefits from larval export will outweigh increased mortality outside reserves due to displaced fishing effort, but that these benefits will be challenging to detect due to their diffuse nature. This synthesis study provides a framework that can be used to generate realistic predictions of the spatial scale, magnitude and detectable signal of larval export, guide the design and monitoring of marine reserve networks, and refine theoretical predictions in light of empirical evidence.