Date of Award

12-2025

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Degree Statement

Doctor of Philosophy in Oceanography

Department

Department of Oceanography

Granting Institution

University of Alaska Fairbanks

Committee Chair

Kelley, Amanda

Committee Member

Mincks, Sarah

Committee Member

Miller, Cale

Committee Member

Hennon, Gwenn

Committee Member

Doherty, Shannon

Table of Contents

Chapter 1: General introduction

Chapter 2: Seasonal trophic resource partitioning by the Pacific oyster (Crassostrea gigas) and the Pacific blue mussel (Mytilus trossulus) in an Alaskan estuary

Chapter 3: Spatial variability in zooplankton consumption by the Pacific oyster (Crossostrea gigas) relative to native bivalves in the Gulf of Alaska

Chapter 4: Quantifying farmed kelp atmospheric CO2 uptake through localized air-sea flux in the northern Gulf of Alaska.

Abstract

The rapid expansion of mariculture in Alaska can drive physical and chemical alterations to the marine environment by introducing non-native organisms or artificially increasing the biomass of a native species. Currently, the main mariculture products grown in Alaska include the Pacific oyster (Crassostrea gigas), the Pacific blue mussel (Mytilus trosuslus), and three macroalgae species: ribbon kelp (Alaria marginata), sugar kelp (Saccharina latissima), and bull kelp (Nereocystis luetkeana). This dissertation examines how these species can impact their surrounding environment to better inform management practices for this growing industry. This research characterized the resource use of C. gigas and M. trossulus seasonally and regionally across the Gulf of Alaska, revealing that the non-native C. gigas may occupy a new dietary niche within the marine environment and create a new predatory pressure upon the zooplankton community. This finding could position C. gigas as a successful colonizer if temperatures rise and these shellfish acquire the ability to reproduce in Alaska’s cold waters, necessitating consideration for their ecosystem impact. However, C. gigas and M. trossulus also consumed detrital macroalgae, supporting co-culturing shellfish with macroalgae. Additionally, this research investigated the ability of macroalgae farms to drawdown atmospheric carbon dioxide (CO2) and whether fluxes varied across the three sites in the Gulf of Alaska. The site-specific CO2 drawdown rates demonstrated that macroalgae farms may act as both a source and sink of CO2 to the atmosphere. Despite the observed transition from heterotrophy to autotrophy in spring across all three sites, the atmospheric CO2 flux varied from positive to negative within the span of hours due to variable wind forcing and disequilibrium between the ocean and the air. These results suggest that selling carbon credits from kelp farms in Alaska would require site-specific analyses and a greater understanding of the other sinks of macroalgae (such as the dissolved and particulate fraction). Combined, these findings indicate that aquatic farms can affect marine ecosystems, highlighting the need to manage the potential impacts of both native and non-native mariculture products on the environment.

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