First Advisor

Yangdong Pan

Term of Graduation

January 2023

Date of Publication


Document Type





fatty acids, harmful algal blooms, phytoplankton, socio-ecological systems

Physical Description

1 online resource ( pages)


Plankton productivity supports estuarine food webs, and has been tied to the success of fisheries, macroinvertebrates, and cultured shellfish yields. Climate change and alterations to nutrient loads are thought to be influencing plankton assemblages, with toxin-producing harmful algal blooms (HABs) on the rise and nutritional quality of plankton declining globally. These shifts in plankton communities may contribute to low biomass yields and toxin-based closures of important fisheries. The objectives of this dissertation are to identify environmental drivers, trophic impacts, and management strategies to understand and respond to changing estuarine plankton communities. To address these objectives, I used a combination of field research in multiple Oregon estuaries to understand environmental drivers of plankton communities, a laboratory-based nutrient addition experiment to investigate the impacts of nutrients on the nutritional quality of plankton, and a social science survey to probe shellfish harvester exposure to algal toxins and their perceptions of risk. I found that discharge shifted plankton communities of the Lower Columbia River Estuary during marine heat waves, favoring the development of two different HABs via two different mechanisms. These HABs included a bloom of Pseudo-nitzschia spp. driven by upwelling and subsequent advection into the estuary, and an in situ bloom of Gymnodinium catenatum fueled by an organic nutrient source and long residence time. I also found that nutrient conditions impact plankton nutritional value, as measured by the biomarker of polyunsaturated fatty acids (PUFAs). This relationship was modulated by seasonality, and high PUFA content emerged through either inorganic or organic nutrient uptake. Finally, I found that combining social and ecological datasets improved assessment of risk of exposure to algal toxins, and that certain demographic groups displayed gaps between their perceived and actual risk of exposure to algal toxins. This research aims to understand plankton regime transitions in toxicity and nutritional value under anthropogenic impact scenarios, and informs management in changing socio-ecological systems. In this dissertation, I identified drought conditions and the summer season as high-risk for estuarine HABs and shellfish harvester exposure to algal toxins. I also found that estuarine plankton can attain high nutritional value via uptake of multiple types of nutrients, providing a high-quality food resource for consumers in these habitats. This information will be useful for adapting future management of estuarine plankton, and has implications for estuarine ecosystems, fisheries, coastal economies, and human health and nutrition.


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Available for download on Saturday, February 01, 2025