Connectivity Fecundity And Larval Abundance Along An Upwelling Coast

A better understanding of the processes that regulate marine metapopulations is needed for effective conservation management planning. Ecosystem level protections in the form of marine protected areas (MPAs) may be the most effective strategy to minimize the risk of population collapse, community disruption, and biodiversity loss because intact communities appear to be more resilient to natural and anthropogenic disturbances. The effectiveness of MPAs as a tool for conserving marine populations, however, hinges on understanding the processes that regulate marine populations. This dissertation focuses on three connected processes that play large roles in regulating marine metapopulations - population connectivity, fecundity, and larval distribution. I investigate these processes in decapod populations along an open coast characterized by strong seasonal upwelling that drives high primary production and rich marine biodiversity and supports a plethora of fisheries. In Chapter 1, I used extensive field measurements of fecundity, population size, and settlement and a Bayesian modeling approach to determine demographic connectivity among invertebrate populations along the California coastline. This study provides the first evidence of high local retention and limited connectivity among populations spanning 700 km along an open coast in an upwelling system with larvae that spend approximately six weeks in the plankton. The Bayesian modeling approach employed to estimate larval dispersal revealed the importance of employing demographic data in these estimates. The approach provides a tractable framework for addressing these questions for species occurring in discrete coastal populations. Latitudinal variation in upwelling affecting larval supply via advection offshore is widely considered to regulate populations and communities in upwelling regimes. In Chapter 2, I investigated an alternative explanation for differences in recruitment along the west coast of the U.S. - whether variation in fecundity could explain differences in recruitment across the two upwelling regimes that occur between Washington and California. Fecundity varied between upwelling regions, likely due to previously documented differences in primary productivity, and locally, depending on habitat type and surfzone hydrodynamics, both of which likely affect access to food. Larval distributions provide us with the clues to determine larval transport and survival. In Chapter 3, I determined the degree to which decapod larval abundance and spatial distribution are affected by local, regional, and basin-scale oceanographic conditions interannually. This investigation revealed that environmental variability, predominantly related to upwelling and primary production, explained 5% - 20% of the variability in the larval distributions, and the spatial distributions found in previous temporally constrained studies remained generally consistent across 8 years. The findings indicate that larval behaviors and demographic variables likely play a more important role in larval distributions than physical forcing. Effective spatial conservation management relies on understanding population persistence, which requires knowledge of population connectivity, fecundity, and the drivers of larval abundance through time. Taken together, these investigations into processes that regulate marine populations along a productive upwelling coast advance our fundamental understanding of the ecology and evolution of life in the sea and provide insights to improve management and conservation of its resources and ecosystems.