UC Santa Barbara

The oceans face increasing pressure from human activities. Land-based activities drive the runoff of pollutants into coastal waters where they can disturb or destroy natural habitat, while ocean-based activities can lead to the unsustainable extraction of marine resources, add additional pollutants, and disrupt biodiversity and ecosystem function. Yet, stewarding marine spaces intentionally can increase ecosystem function while deepening our understanding of these complex systems. Using a mix of spatial modeling and causal inference, the following dissertation, in three chapters, describes and presents solutions to improve stewardship of marine environments in the United States (US), considering our relationship with oceans from end to end. My first chapter describes and applies a novel tool to better understand the distribution of pollution from human activities, the second chapter proposes a strategy to mitigate the impacts of coastal nutrient pollution, and finally, my third chapter reveals key insights from our most intimate and foundational relationship with the ocean, our consumption of seafood. Each of these chapters is the product of long running, multi-disciplinary collaborations.

In the US, nitrate loading into marine environments has been relatively constant at a high input level over the past 20 years, while phosphate loading has continued to increase. In some places, excess nutrients drive cascading ecosystem changes, in others, despite significant additional nutrient loads, ecosystems are better able to absorb these impacts. In my first chapter, alongside collaborators, I identify pollution “hotspots” in continental US coastal waters where anthropogenic nutrient loading is high compared to natural nutrients in order to

help drive water quality management. We adapted generalized plume models for river and sewage to model the dispersal of anthropogenic nutrients into marine environments, we then combine model outputs with atmospheric N deposition, overlaying these with nutrient data from published sources (annual totals (kg/yr), 0.2 degree raster cell). We find nutrient pollution hotspots concentrated in the Northeast, US and in the Gulf of Mexico, however, some high-nutrient settings, like Southern California, have significant nutrient pollution in localized settings. This work contributes a novel application of generalized plume models that efficiently analyzes the transport and distribution of nutrient pollution at regional and national scales.

Given the severity of coastal nutrient loading, my second chapter explores a potential solution: strategic placement of seaweed aquaculture. Seaweed is capable of removing large quantities of nitrogen and phosphorus from coastal ecosystems, yet seaweed has gained little traction for its potential role in targeted nutrient assimilation. Marine nutrient pollution is increasing around the world, contributing to expanding eutrophic conditions and co-occurring with other stressors that impact the state and stability of aquatic ecosystems. In the US, climate change, legacy nitrogen, and nonpoint source pollution make it increasingly difficult to curb growing eutrophication and the associated effects, such as hypoxia (dissolved oxygen < 2 mgL-1). Employing a synthetic semi-quantitative approach, we use the Gulf of Mexico as a case study – a US priority area for aquaculture with substantial nutrient pollution and one of the largest hypoxic zones on the planet – to assess the potential for native seaweed

aquaculture to augment upstream pollution control with downstream nutrient assimilation. Results from this analysis suggest that given growing market demand, new product pathways, and nutrient pollution markets, seaweed aquaculture may be a feasible tool for nutrient assimilation that could subsidize, if not pay for itself.Finally, my third chapter explores the impact of consumption on marine resources. Shifts in food access due to the COVID-19 pandemic were heterogeneous, offering a unique chance to differentiate the effects of restaurants, public assistance programs, and consumer attitudes on purchasing behavior. We use California’s novel tiered COVID-19 restriction system, which imposed top-down county-level economic restrictions dependent on caseloads and testing rates, as a natural experiment to untether the effects of changing seafood access. We deployed a longitudinal survey (N=464) to capture seafood consumption patterns for the same population of Californians three times between August 2020 and August 2021. To casually identify marginal shifts in consumption behavior due to changing seafood access (i.e., food service restrictions and county-level factors) we use two-way fixed effects models. In parallel, we assess relationships between consumption at the species-level using network analyses. Nuanced purchasing behaviors, such as purchases of specific species (e.g. shrimp, salmon, and local species) and products (e.g. canned, fresh) became more entrenched given disruptions to access. Diversity of seafood consumption, however, remained unchanged from pandemic disruptions, shifting instead in response to individual attitudes. We find a personal relationship with seafood is the most pervasive driver of seafood consumption.