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Date of Award

Spring 2023

Document Type

Masters Thesis

Department or Program Affiliation

Biology Department

Degree Name

Master of Science (MS)



First Advisor

Olson, M. Brady (Michael Brady)

Second Advisor

Lemkau, Karin

Third Advisor

Van Alstyne, Kathryn Lyn, 1962-


In coastal, nutrient-rich waters like the Salish Sea, diatoms dominate the phytoplankton community during seasonal upwelling events. Diatoms were once believed to be an ideal food source for primary consumers like copepods, but their role in food web dynamics changed upon discovery that diatoms can produce organic compounds upon cell death known as polyunsaturated aldehydes (PUAs). These compounds directly affect the reproductive success of diatom consumers by reducing egg production and viability, deforming embryos, and delaying embryonic development. PUA production dynamics have been assessed under varying nutrient concentrations and culture age, but no study has tested the effect of elevated dissolved CO2 (pCO2) on the production of these organic molecules. In addition, most surveys of PUA-producing diatoms have only assessed pelagic production. In this study, I isolated benthic diatom species from the Salish Sea and tested them for PUA production. I also conducted a microcosm upwelling experiment using a benthic and pelagic diatom under varying pCO2 levels to assess whether PUA production is affected by inorganic carbon level.

I found that all Salish Sea benthic diatom species tested produced PUA molecules, and elevated pCO2 did not significantly affect the production of PUA molecules. Experimental results indicate that upwelling events alone are likely not causing an increase in PUA production. The survey results indicate that benthic diatoms should be included in future PUA producer surveys to assess PUA production in the water column. Future research should assess the synergy between elevated pCO2 and nutrient limitation on PUA production, as these conditions are expected with worsening climate change. In addition, future studies on the impact of PUAs on grazer fecundity should be expanded to include benthic diatom consumers, including mollusks and other benthic invertebrates.




Diatom, Polyunsaturated Aldehyde, PUA, Benthic, Salish Sea, Skeletonema, Fragilariopsis, Carbonate Chemistry, Fecundity


Western Washington University

OCLC Number


Subject – LCSH

Diatoms--Salish Sea (B.C. and Wash.); Upwelling (Oceanography)--Salish Sea (B.C. and Wash.); Climatic changes--Salish Sea (B.C. and Wash.); Marine microbiology--Salish Sea (B.C. and Wash.)

Geographic Coverage

Salish Sea (B.C. and Wash.)




masters theses




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