UC Santa Cruz

Studying the movement ecology and ecophysiology of marine megafauna is critical for understanding how increased stressors will overlap with species distribution and affect species behavior, which will ultimately have ecological consequences. Warming water temperatures and ocean deoxygenation will likely alter habitat suitability for marine megafauna either directly through physiological impact or indirectly through shifting prey distributions. Previous studies have shown that the horizontal distribution of marine predators can be explained by the temperature-dependence of predation success and metabolism. However, temperature and oxygen vary drastically in the vertical dimension. These vertical gradients influence metabolism, behavior, and predation success but remain understudied despite advances in biotelemetry that permit investigating movement in four dimensions (i.e., 3D space and time). To address this gap, my dissertation investigates how physiological demands and environmental factors, specifically temperature and oxygen, influence the diving behavior and ecophysiology of marine megafauna. First, we reviewed current knowledge on the thermoregulatory strategies of air-breathing marine vertebrates and synthesized the complementary contributions of lab and field studies (Chapter 1). We then focused on reviewing the dynamic role of blubber and peripheral perfusion for marine mammal thermoregulation and demonstrated the potential of physio-logging to advance our studies of thermoregulation in an ecologically relevant context (Chapter 2). Using northern elephant seals (Mirounga angustirostris) as a model species, we performed at-sea experiments with custom-made biologgers and examined novel physiological data showing fine-scale changes in thermal responses while diving (Chapter 3). Unlike water temperature, dissolved oxygen data is limited resulting in few efforts to understand how oxygen affects diverse marine megafauna, particularly the indirect effects on air-breathers. We investigated the diving and foraging behavior of an air-breathing mesopelagic predator in relation to dissolved oxygen and found that elephant seals primarily use the oxygen limited zone rather than the oxygen minimum zone as previously hypothesized (Chapter 4). Overall, this dissertation contributes a new ecologically relevant understanding of marine megafauna movement in three dimensions. Expanding and synthesizing such studies across various marine taxa is critical for understanding how changing ocean conditions (e.g., warming waters and ocean deoxygenation) will differentially affect marine species and ultimately ecosystem structure and function.