Date of Award

Fall 12-2025

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Ocean & Earth Sciences

Program/Concentration

Oceanography

Committee Director

Margaret R. Mulholland

Committee Member

Kenneth N. Mertens

Committee Member

Alexander Bochdansky

Committee Member

Todd Egerton

Abstract

Margalefidinium polykrikoides is a harmful cosmopolitan dinoflagellate that blooms in coastal waters. The effect of temperature and salinity on the growth of M. polykrikoides VA strain was examined using microscopy and growth models. M. polykrikoides Group III VA strain grew better at warmer temperatures and lower salinities than M. polykrikoides Group III NY strain, Group I Korea strain, and Japan strain (unknown group). Modelers need to use the temperature and salinity growth responses from M. polykrikoides Group III VA strain to better simulate and predict M. polykrikoides blooms in the Chesapeake Bay.

Dinoflagellates produce cysts as a strategy to withstand environmental stressors, with nutrient depletion generally considered a key trigger for cyst production. M. polykrikoides is known to produce both pellicle (single layer thin wall) and resting cysts (thick wall with one to three layers), whereas its congener, Margalefidinium fulvescens has been shown to produce sac- or pumpkin-like structures in culture. In this dissertation, I studied for the first time sac-like pellicle cysts from M. polykrikoides Group III VA strain in culture and in the Lafayette River, a subtributary of the Chesapeake Bay using phase-contrast microscopy, time-lapse microscopy, FlowCam, and Attenuated total reflection Fourier-transform infrared microscopy (ATR micro-FTIR). Phosphate depletion of the culture medium was determined as the main trigger for sac production,while in the field the trigger is unknown. Sacs were produced through sexual or asexual processes. I observed “sac transporters”—diploid cells enabling sac movement—for the first time in culture. ATR micro-FTIR spectra indicated that the sacs are primarily composed of sulfated polysaccharides, showing a strong resemblance to the extracellular polymeric substances produced by M. polykrikoides Japan strain and by Gymnodinium A3. Multiple sacs were observed in the water column in the field during summer and fall (when no bloom was present) and one in the sediments during spring. The sac from the sediments responded to stimulus, but it did not germinate. M. polykrikoides Group III VA strain seems to be forming sac-like pellicle cyst as a protection mechanism. Sac-like pellicle cysts could potentially have dual functionality and be part of the Chesapeake Bay seed bank.

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DOI

10.25777/tc9d-jj31

ISBN

9798276041452

ORCID

0000-0002-4783-3881

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