ESTIMATING PARTICLE DISPERSAL IN AQUATIC SYSTEMS: A COMPARISON OF NEW AND CONVENTIONAL TECHNOLOGIES

Abstract

Dispersal is one of the most important life history strategies involved in species survival and evolution, affecting population dynamics, population genetics, and the spatial scale of population connectivity through the exchange of individuals among geographically separated subpopulations. Aquatic species exchange individuals, and subsequently genes, among subpopulations mainly through early life-stage dispersal; however, the dominant scales of dispersal are still “not known” and the knowledge of how aquatic populations are connected in space and time is thus limited. The extent of early life-stage dispersal is dependent on physical (e.g., advection and diffusion) and biological (e.g., reproduction, behavior, and mortality) processes, and interaction among these physical and biological processes makes distinguishing their separate effects on dispersal challenging. Motivations to study and quantify dispersal and connectivity range from biodiversity conservation to the design of marine reserves and the mitigation of species invasions. Since robust measures of dispersal in aquatic environments are rare, when they are obtained, they must be used to test the assumptions and hypotheses of the numerical models that are often used as the basis of management and conservation decisions. I quantify the dispersal of purely passive particles at the scale of early-stage planktonic organisms in the near-surface upper mixed layer of coastal ocean and lake environments using a new magnetically attractive particle (MAP) and magnetic-collector prototype system that provides a time-integrated estimate of the purely passive component of dispersal from a given source location to a large set of potential sink locations; the biological null model. The quantitative, empirical estimates that the MAPs provide can be used to test other technologies that estimate dispersal, and I qualitatively and quantitatively compare the observed passive particle dispersal estimates to similar estimates derived from hydrodynamic models and concurrently deployed drogued drifters. I illustrated the results in the context of issues surrounding commercially valuable and (or) invasive species, and discussed the limitations of using the various technologies, especially models, to address dispersal and connectivity questions. This thesis has made an advance toward linking the empirical with the theoretical.