Theses and Dissertations

Date of Award

12-2024

Document Type

Thesis

Degree Name

M.S.

Department

Marine Sciences

Committee Chair

Jeffrey W. Krause

Advisor(s)

Kenneth Hoadley, Alison Robertson

Abstract

Phytoplankton play a crucial role in marine ecosystems due to their innate ability to fix carbon. As atmospheric CO2 levels continue to rise from fossil fuel combustion, the resulting increase in dissolved CO2 and the concurrent decrease in ocean pH are likely to impact the phytoplankton community. The response of phytoplankton to elevated CO2 can vary significantly among species and environmental conditions (e.g. light, temperature, nutrient availability). To address these variations, an experiment was conducted using a controlled photobioreactor system, maintaining high and low light, constant temperature, nutrient levels, and two pCO2 concentrations. This study focused on two regionally relevant phytoplankton in the northern Gulf of Mexico. Skeletonema (a diatom) increased growth rates with the combination of high light and high carbon, but this was not accompanied by increases in particulate organic carbon and nitrogen (POC/N). In contrast, Micromonas commoda (a green alga) did not show changes in growth rate or POC/PON but allocated more energy towards photosynthesis. Additionally, Skeletonema displayed a decoupling between growth rate and silicification, leading to higher biogenic silica content per cell in elevated pCO2 environments. These results highlight the necessity for genera-specific and regionally focused research, as the physiological plasticity among phytoplankton can vary.

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