A genetic investigation of the population connectivity of Paralabrax clathratus (kelp bass), a temperate reef fish

Population genetic techniques can be useful in characterizing dispersal when monitoring movement of individuals directly is challenging. The difficulty of studying the dispersal of marine species has long challenged our basic understanding of the scales and patterns of population structure in the sea. I use microsatellite genetic markers to investigate the population structure and genetic diversity at large and small spatial scales for Paralabrax clathratus, a top predator on the reefs and kelp forests between southern Baja, Mexico and Point Conception, California. In Chapter One, I provide an overview of the use of microsatellites as population genetic markers and present a novel protocol for ensuring a high-quality set of microsatellite markers. In Chapter Two, I examine the impact of a striking bimodal spatial pattern in population density over the species' range on genetic structure of P. clathratus. Heterogeneity in density creates heterogeneity in heterozygosity across populations which obscures an isolation-by-distance effect for the lower mutation rate loci, but not the higher mutation rate loci. This phenomenon may be a common explanation for the prevalence of 'chaotic genetic heterogeneity' observed for marine species. In Chapter Three, I test competing hypotheses about the large-scale patterns of connectivity for kelp bass and other temperate reef fishes that span the US/Mexico international border, using a combination of new genetic data and CalCOFI ichthyoplankton data. The results suggest these reef fishes in the Southern California Bight are likely reliant on local reproduction to sustain them instead of mainly depending on periodic long-distance dispersal of larvae from Mexico during El Nino flow reversals, as was previously widely assumed. Chapter Four tests alternate hypotheses about the root of small-scale genetic structure in bi-weekly collections of P. clathratus recruits at sites in the Santa Barbara Channel. The data failed to the support hypotheses of environmental selection or sweepstakes reproductive success, although several of the cohorts showed strong evidence of containing a small fraction of siblings. Instead, correlations of genetic patterns with the direction of flow suggest temporal variation in the direction of larval delivery is responsible for the changes in the genetic composition of recruits.