Date of Award

12-2025

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Degree Statement

Doctor of Philosophy in Marine Biology

Department

Department of Marine Biology

Granting Institution

University of Alaska Fairbanks

Committee Chair

Iken, Katrin

Committee Member

Horstmann, Lara

Committee Member

Hennon, Gwenn

Committee Member

von Biela, Vanessa

Committee Member

McMeans, Bailey

Table of Contents

Chapter 1: Introduction

Chapter 2: Getting to the source of it: determining the specificity of different biomarkers distinguishing primary producers

Chapter 3: Consistent trophic structure but weak seasonal trends in benthic food webs within Arctic lagoons

Chapter 4: Patterns of trophic niche overlap of diadromous and marine Arctic fishes in Beaufort Sea coastal lagoons

Abstract

The rapid loss of sea ice, warming waters, and increasing freshwater inputs are altering Arctic coastal lagoons, ecosystems that support diverse invertebrate communities, fishes, and subsistence harvests. To resolve how trophic interactions in these systems function under strong seasonal and spatial variability, I applied multiple biochemical tracers, specifically bulk δ13C and δ15N, compound-specific stable carbon isotopes of essential amino acids, and fatty acids to characterize organic matter sources and better understand the trophodynamics of benthic invertebrates and fishes in Beaufort Sea lagoons. I first established local biomarker baselines for terrestrial, microalgal, and macroalgal producers, showing that no single tracer could fully distinguish among sources, but that a combined approach could improve resolution. Secondly, I used bulk stable isotope analyses of benthic invertebrates across seasonal conditions of ice cover, break-up, and open water, revealing consistent niche partitioning in feeding groups but weak seasonality in the overall food web structure. Instead, the benthic food web seems to rely on a mixed sediment food source across seasons, which buffers and stabilizes the food web against seasonal shortfalls of organic matter provision. Lastly, I compared diadromous and marine fishes between high and low marine exchange lagoon types, finding broader trophic niches in diadromous species but consistent overlap across life histories, particularly in high exchange lagoons. This research demonstrates that multiple strategies, such as trophic plasticity, resource partitioning, reliance on consistent food sources are central to maintaining the stability of Arctic lagoon food webs under shifting environmental conditions. By integrating multiple biomarkers in studies across taxa and seasons, these findings provide critical baseline knowledge to forecast ecosystem responses to climate change and to inform the management of subsistence fisheries in northern communities.

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