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Date of Award

Winter 2023

Document Type

Masters Thesis

Department or Program Affiliation

Marine and Estuarine Sciences

Degree Name

Master of Science (MS)



First Advisor

Dr. Michael Brady Olson

Second Advisor

Dr. Katherine Van Alstyne

Third Advisor

Dr. Ruth Sofield


In the Salish Sea, blooms of the intertidal macroalgae, Ulvaria obscura, are common and can achieve extraordinarily high biomass. Upon desiccation and subsequent rehydration from incoming tides, U. obscura releases dopamine. Previous studies showed that dopamine negatively affects other macroalgal species and can deter grazers. However, the effects of dopamine on co-occurring phytoplankton remains unknown. This study explored the toxicity of dopamine on four phytoplankton known to inhabit the Salish Sea: the haptophyte, Isochrysis galbana; the chlorophyte, Dunaliella tertiolecta; the dinoflagellate, Heterocapsa triquetra; and the diatom, Thalassiosira sp. Over the course of 8 days, phytoplankton growth was monitored across six dopamine concentrations ranging from 0 to 240 μM dopamine. This concentration range of dopamine represents concentrations observed in laboratory experiments. Dopamine reduced phytoplankton growth in all species; however, the concentration at which intrinsic phytoplankton growth rates were reduced was species-specific. Based on IC50 estimates, H. triquetra, Thalassiosira sp., and I. galbana were the most and equally sensitive to dopamine, while D. tertiolecta was the least sensitive. The intrinsic growth rates in Thalassiosira sp. and H. triquetra recovered after four days of dopamine exposure in the high dopamine treatments. Results from this study showed that dopamine exposure significantly decreased phytoplankton intrinsic growth rates for all species tested, and that after an initial decline in growth, two species recovered and achieved pre-exposure intrinsic growth rates. This suggests that in the presence of dopamine, phytoplankton community structure may be influenced by species-specific sensitivity to dopamine, whereby dopamine-tolerant species come to dominate these communities.




Phytoplankton, green tides, dopamine, toxicity, algae, Salish Sea, marine, intertidal, macroalgae, diatom


Western Washington University

OCLC Number


Subject – LCSH

Marine phytoplankton--Salish Sea (B.C. and Wash.); Marine algae--Salish Sea (B.C. and Wash.); Dopamine; Toxicity testing--Salish Sea (B.C. and Wash.)

Geographic Coverage

Salish Sea (B.C. and Wash.)




masters theses




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