Marine predator effects on ecosystem function and connectivity across spatiotemporal scales
Keywords: Humanities and Sciences.
Biology.

Marine predator populations worldwide are experiencing ubiquitous declines from a myriad of anthropogenic threats, including over harvesting, by-catch, and ecosystem degradation due to climate change. However, many of the ecological consequences of these losses are poorly understood, particularly regarding how they may influence biological connectivity and the overall function of marine ecosystems. Large mobile consumers create functional and energetic linkages between physically separated habitats as they feed on diverse prey populations. These interactions have important consequences for food web structure, habitat connectivity, and ecosystem stability, yet our understanding of these connections is still largely theoretical, especially regarding how these effects scale across time and space. In this dissertation I investigate the role of mobile marine predator roles in shaping ecosystem function and connectivity through three studies conducted at differing spatial scales in the North Pacific. In Chapter 1, I use a stable isotope (SI) aggregate dataset compiled from the literature to construct novel multi-taxa isoscapes and investigate large-scale trophic dynamics across Longhurst biogeographic provinces. Results indicate that baseline isotopic signatures are consistently propagated up through regional food webs and, further, that global modeled phytoplankton isoscapes may be a viable tool for predicting consumer SI ratios across trophic levels and regions. This chapter furthers fundamental knowledge of how large-scale existing datasets might be harnessed to study regional trophodynamics and mobile predator movement. Chapter 2 presents an examination of how spatiotemporal scale effects the interpretation of large spatial datasets for highly migratory marine predators and consequences for understanding life history and vulnerabilities. Using satellite tracking data for 128 female salmon sharks (Lamna ditropis), I identify previously unknown distribution patterns and potential foraging hotspots as well as potential overlap with commercial fishing effort in the California Current region, an area where they have been previously described but whose role has been poorly understood. Based on known life history and hypotheses in the literature, I conclude that this region might provide critical foraging habitat related to complex multi-year reproductive cycles, demonstrating the importance of its consideration in future management and conservation. In Chapter 3, I investigate the ecological traits and conditions underlying cross-ecosystem dietary reliance among a diverse group of predatory fish species in a coral reef-open ocean system. I collected SI carbon and nitrogen data for 33 fish species and found significant evidence that dietary mixing occurred across all predator species and guilds sampled. Primary habitat association, water column use, and diet strategy appeared to be the primary determinant of dietary mixing, with mobile reef mesopredators being the most dependent on cross habitat resources. I conclude that SI data in combination with life history knowledge might be used to predict the occurrence of cross-ecosystem provisioning and its implications for marine spatial management and conservation. Overall, this dissertation fills knowledge gaps of how mobile marine predator shape and connect marine ecosystems and emphasizes the importance of considering how these interactions scale across habitats and ecoregions for ecological understanding and guiding the management and conservation of predator populations and their ecosystems.