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Biophysical Responses of Plankton to Natural and Human-Driven Environmental Variability in the California Current


Plankton play an essential role in marine ecology as the base of ocean food webs and, in the case of marine larvae, as the next generation of marine populations. Consequently, understanding how oceanography and environmental conditions impact the distribution, abundance, and condition of plankton is fundamental to both community ecology and population dynamics. However, the miniscule size of plankton relative to the scale of their pelagic environment makes it uniquely difficult to examine biophysical processes of plankton in the field. In this dissertation, I present three studies documenting the findings from field-based investigations of plankton biophysics across scales in the California Current Ecosystem on the North American West Coast. In chapter one, I examine the influence of the 2014-2016 marine heatwave and El Niño event on the body size of krill off the coast of California and show that the length of two temperate krill species declined during the heatwave, while the size of a third subtropical species increased. In chapter two, I document, for many species for the first time, the existence of discrete depth preference behaviors among larval fishes that mediate dispersal trajectories across and along the continental shelf of northern California. In chapter 3, I test the hypothesis that small-scale, ephemeral, and topographically generated fronts forming on the poleward side of a small headland during relaxation flows create spatial heterogeneity in nearshore plankton assemblages. Although the front surveyed proved to be transient and weak, it did appear to act as a barrier segregating offshore and onshore plankton communities. Together, these studies offer portraits of how biophysical interactions in the plankton may impact ecological processes from local to ecosystem scales and highlight their importance for management and conservation of marine systems in an era of climate change.

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