Population connectivity in a dynamic coastal system: Effects of mesoscale eddies on distribution, growth, survival, and transport of larval reef fishes

Population connectivity (i.e., the exchange of individuals among geographically distinct subpopulations) is an issue of particular relevance in the marine environment, as the majority of benthic marine organisms have complex life cycles and dispersal events occurring in the early life stages are nearly impossible to track. As the magnitude and direction of larval dispersal are shaped ultimately by larval distributions, growth, mortality, and transport to adult habitat, this dissertation examined these processes for larval reef fishes in the Straits of Florida (SOF) to contribute to the understanding of patterns of population connectivity along a continental coastline. An analysis of spatially and temporally extensive ichthyoplankton collections and associated environmental data demonstrated that environmental variation through the vertical water column was most important in structuring larval assemblages in the SOF and that horizontal patterns in larval assemblages were only weakly related to oceanographic features (i.e., mesoscale eddies, ME, and the Florida Current). However, otolith analysis revealed that residence in MEs enhanced larval growth for four out of the five reef fish species examined, and this increased growth was consistent across three sampling periods and two years. These results indicate that MEs provide enhanced feeding environments for larval reef fishes. Additional otolith analysis of cohorts of two reef fishes tracked from the pelagic environment to the reef (i.e., settlement-stage), demonstrated that for one species (Cryptotomus roseus) slow-growing larvae were selectively removed from the population just prior to settlement. In this same species, slow-growing larvae from offshore waters did not contribute to the surviving population of settlement-stage larvae, suggesting that for at least some species and settlement events, upstream Caribbean fish populations are not well-connected to populations in the SOF. Finally, several lines of evidence, including temporal changes in larval assemblages and patterns of larval abundance and age across water masses, are consistent with the existence of nearshore retention of locally-spawned larvae in the SOF and, thus, the potential for self-recruitment in reef fish populations of the Florida Keys.