UC Santa Cruz

Natural and anthropogenic environmental changes are impacting marine species worldwide. However, our understanding of how changes to multiple environmental drivers impact the physiology and ecology of organisms is still largely unknown. Kelp forest ecosystems along the coast of California present a unique system to assess how environmental variability (both natural and human-induced) impacts key species of concern. In particular, these biodiverse ecosystems reside within the California Current System, which is characterized by dynamic oceanographic conditions that vary across latitude largely due to differences in the strength and intensity of coastal upwelling. Furthermore, environmental conditions are predicted to change especially rapidly in this region due to accelerated acidification, deoxygenation, and warming. In this study I first use ecologically and economically important grazer taxa to understanding how current and future environmental changes impact the physiology and ecology of marine organisms. Secondly, I conduct a synthesis of multiple driver experiments across ecosystems to assess the generality in interactive effects of warming and ocean acidification. In chapter one, I use insitu monitoring of pH, temperature, and dissolved oxygen conditions within a central California kelp forest to further understanding of the relationships between environmental conditions across seasons. I then use these environmental relationships to undertake a manipulative laboratory mesocosm experiment to assess how upwelling impacts the physiology and ecology of the gastropod, Promartynia pulligo, and the echinoderm, Mesocentrotus franciscancus. In chapter two, I expand monitoring of pH, temperature, and dissolved oxygen to northern and southern California kelp forests to better understand differences in the coupling of environmental drivers across regions that experience strong versus weak upwelling. I then conduct a laboratory mesocosm experiment to look for signs of local adaptation of red sea urchins, Mesocentrotus franciscanus, across regions and compare responses of M. franciscanus to region-specific coupled future changes in pH, temperature, and dissolved oxygen. In my final chapter, I zoom out to think more broadly about how multiple environmental drivers interact to alter species responses to warming and ocean acidification. I use a meta-analysis to calculate the frequency of interaction types across seven response variables and eight broad taxonomic groupings. I then assess the relationship between the magnitude of the predicted cumulative effect and the measured cumulative effect to determine when the magnitude of the effect drives the interaction. In this dissertation I show that kelp forest grazers responses to environmental changes vary across species and populations and that broad patterns in how species respond to multiple environmental drivers are likely to be less pronounced than predicted.