Date of Award

Spring 2023

Project Type


Program or Major

Biological Sciences

Degree Name

Master of Science

First Advisor

Elizabeth Harvey

Second Advisor

Robert Letscher

Third Advisor

Kelsey Poulson-Ellestad


Phytoplankton, marine microalgae that are the base of the oceanic food web, significantly influence the flow of essential nutrients throughout marine ecosystems. In particular, phytoplankton have been implicated in the cycling of the vitamin thiamin (B1) and its components 4-methyl-5-thiazoleethanol (HET) and 4-amino-5-hydroxymethyl-2-methylpyrimidine (HMP). These compounds are essential to many marine microbes but are found in relatively small concentrations (<500 pM) throughout the earth’s oceans. Despite the importance of these vitamins in fueling marine microbial growth, very little is understood regarding their sources and sinks. To better understand the impacts of vitamins on phytoplankton growth and interactions with microzooplankton grazers, 20 dilution experiments spiked with additions of B1, HET, or HMP were conducted. These were performed across seasons, and examined changes not only in bulk chlorophyll concentration, but also in size-specific growth and grazing rates. No clear patterns in rate changes in response to additions of B1 or precursors were observed. Additionally, often vitamin addition resulted in compound-dependent significant changes in growth and loss rates. No significant changes in rates were found to correlate with starting phytoplankton abundance, suggesting that the composition of the starting phytoplankton community played a large role in mediating the response to vitamin addition relative to total abundance. Overall, these findings highlight the complexity and importance of understanding the sources and sinks of B1 and its components in the marine environment.