Date of Award

5-2008

Level of Access Assigned by Author

Campus-Only Thesis

Degree Name

Master of Science (MS)

Department

Oceanography

Advisor

Mary Jane Perry

Second Committee Member

Mark L. Wells

Third Committee Member

Maxim Gorbunov

Abstract

Phytoplankton live in a dynamic environment and are capable of changing and adapting to varying levels of light and nutrients. As phytoplankton adjust to their environment their intrinsic properties such as absorption and fluorescence change on relatively short time scales (hours). We document rapid changes in phytoplankton specific absorption, variable fluorescence (Fv/Fm), and chlorophyll a fluorescence intensity (fluorescence normalized to extracted chlorophyll; F/Chl) in a series of day-long time courses. In a stratified basin in the Gulf of Maine we see large increase in phytoplankton absorption of ultraviolet light corresponding with maximum irradiance midday. The change in absorption suggests an adaptation in response to high light that alters the concentration or composition of photoprotective ultraviolet-absorbing compounds such as mycosporine-like amino acids (MAAs). Variable fluorescence (Fv/Fm) and Chlorophyll a intensity (Fluorescence normalized to chlorophyll; F/Chl) were measured for a series of experimental and in situ time courses to examine diel changes in different nutrient and light regimes. In situ samples were taken from a nutrient replete well mixed estuary (Damariscotta River Estuary, Maine, USA), a nitrogen limited well stratified basin (Wilkinson Basin, Gulf of Maine), and a weakly stratified iron limited high nitrate low chlorophyll (HNLC) region of the north Pacific (Ocean Weather Station Papa). Nutrient level was found to set the maximal morning value of Fv/Fm which is then quenched under conditions of high light by up to -50%. The degree to which Fv/Fm is quenched is dependent on the immediate light level at the time of sampling and the light history of the phytoplankton which is dependent on the mixing regime. The variability in these intrinsic phytoplankton properties illustrates the importance of analyzing fluorescence and absorption data with knowledge of the time of day, light level and light history of phytoplankton.

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