UC San Diego

Predicting ecological responses to changing ocean conditions is particularly challenging in highly dynamic marine ecosystems subject to multiple anthropogenic stressors. My dissertation centers upon understanding fine- and broad-scale patterns that affect energy flow through the California Current Ecosystem (CCE), a dynamic coastal upwelling zone in the eastern Pacific Ocean. I focus on trophic relationships between top predators and their prey by using an iconic indicator species – the California sea lion (Zalophus californianus; sea lions) – and a complex of key forage species to elucidate food web dynamics in the ecosystem.

In Chapter 1, I explore fine-scale temporal, spatial, and physiological patterns that drive the quality of prey species to top predators in the CCE and use bomb calorimetry to generate a novel dataset of energetics information on these forage species. I then integrate my findings with published data on the bioenergetics of sea lions to quantify how predator consumption rates can vary, given the differences in quality I observed within and among prey species. In Chapter 2, I argue that sea lions are an important ecosystem indicator of major food web shifts, which I determined by generating a ~55-year time series of sea lion trophic position using stable isotope analysis of archived tissues coupled with several environmental datasets. My findings demonstrate that regime shifts of two of the most important forage fishes to predators in the CCE can be observed through the trophic lens of sea lions. Sampling of archived tissues to create environmental chronologies is a process laden with error. Therefore, in Chapter 3, I constructed a Bayesian model to quantify the uncertainty in building ecological datasets from growth increment sampling of archived tissues (e.g., teeth, bones). This method can be applied to studies using these structures to create time series of importance for conservation and management questions.

My research fills critical knowledge gaps in our understanding of marine food web dynamics on multiple timescales that will contribute to the literature on community structure and function, while also providing important baseline data that will be useful in assessing future ecosystem states in a time of unprecedented change.