Date Thesis Awarded

5-2023

Access Type

Honors Thesis -- Open Access

Degree Name

Bachelors of Science (BS)

Department

Chemistry

Advisor

Elizabeth Harbron

Committee Members

Amber Hardison

John Poutsma

Nicole Millette

Abstract

Mixotrophic phytoplankton use both autotrophy and phagotrophy, but little is known about their role as prey in aquatic ecosystems. It has been hypothesized that mixotrophs provide a stable food source compared to autotrophs under growth-limiting conditions, but further evidence is needed to support this. To that end, we investigated elemental carbon (C), nitrogen (N), and phosphorus (P) ratios and total lipid content in two mixotrophic and one autotrophic algal culture under varying environmental conditions. Heterocapsa steinii, Scrippsiella sp. (mixotrophic dinoflagellates), and Chaetoceros muelleri (autotrophic diatom) were incubated for 7 days under either Redfield (16:1 N:P) or nitrogen-depleted (4:1 N:P) media and under ambient light conditions (66.4 μE/m2/s) or low light conditions (20% of ambient light). Cultures were sampled before and after incubation for cellular particulate organic C, N, P, and total lipid concentrations. While all cultures had positive growth rates under all conditions, the mixotrophs demonstrated higher overall cellular C, N, P, and total lipid concentrations than the autotroph. Under low light, all species showed lower growth rates, C, N, P, and lipid content. Conversely, under ambient light and nitrogen-depleted conditions, the mixotrophs showed more stable C/N, C/P, and N/P ratios relative to the strict autotroph. This suggests that mixotrophs are a more stable food source than autotrophs. This research has implications for nutrient acquisition of higher trophic levels in ecosystems where mixotrophic and autotrophic algae serve as prey.

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Available for download on Tuesday, May 12, 2026

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