Date of Award

Summer 8-2014

Degree Type

Masters Thesis

Degree Name

Master of Science (MS)

Department

Marine Science

Committee Chair

Donald Redalje

Committee Chair Department

Marine Science

Committee Member 2

Scott Milroy

Committee Member 2 Department

Marine Science

Committee Member 3

William Graham

Committee Member 3 Department

Marine Science

Abstract

Rates of phytoplankton growth and microzooplankton grazing were measured at two locations within the Bay of St. Louis, MS, over the course of three months to explore the dynamics of the phytoplankton community. Community growth rates were estimated based on the changes in chlorophyll a (chl a) concentration using the dilution technique, (Landry and Hassett, 1982) and a C-specific rate was obtained using chl a labeling (Redalje and Laws, 1981). Concentrations of chl a were determined using high performance liquid chromatography (HPLC) and fluorometry. HPLC was also employed to obtain class specific growth and grazing rates, using either marker pigments or the program CHEMTAX. Intrinsic phytoplankton community growth rates (μo) ranged from -0.11 d-1 to 0.49 d-1 and varied based on how chl a was measured. C-specific growth rates ranged from 0.24 d-1 to 0.88 d-1 and were not significantly different (p<0.05) from the nutrient replete community growth rates (μn). Class specific growth rates (μo) ranged from -0.46 d-1 to 0.73 d-1 and varied for all phytoplankton classes. During all samplings, μo was less than μn indicating persistent nutrient limitation of all phytoplankton classes during the incubations. Grazing by microzooplankton accounted for <50% of daily standing stock removal, and grazing rates were often 0 d-1, indicating no significant grazing, and highly variable. The results of this study demonstrate that environmental conditions and microzooplankton grazing both play an important role in controlling phytoplankton composition in the Bay of St. Louis, MS.

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