Date of Award

Fall 12-2011

Degree Type

Masters Thesis

Degree Name

Master of Science (MS)


Marine Science

Committee Chair

Donald G. Redalje

Committee Chair Department

Marine Science

Committee Member 2

Steven E. Lohrenz

Committee Member 2 Department

Marine Science

Committee Member 3

Kjell Gundersen

Committee Member 3 Department

Marine Science


A small-scale study was conducted to determine the effects of light fluctuations on the photosynthetic efficiency of marine phytoplankton. Two species, Phaeodactylum tricornutum and Chaetoceros gracile were grown in specialized photobioreactors on a 12-hour:12-hour light:dark cycle. The cultures were diluted 50% daily to attain a specific growth rate of 0.70 d-1. To simulate vertical mixing in high turbidity habitats under various wind conditions, dense cultures were subjected to fluctuating light treatments with frequencies ranging from 0.10 Hz to 2.00 Hz. Parallel experiments subjected the cultures to static light conditions with equal total daily light doses as those of the cultures in fluctuating light. Aside from the light parameters, all growth conditions remained the same for each paired experiment. Quantum yield was measured using two methods: 14C fixation at the end of the light period to determine maximum quantum yield (Φmax), and increase in depth-integrated particulate organic carbon during the day to determine daily averaged quantum yield (Φave). Photosynthetic efficiency of Photosystem II photocenters was also determined using two types of variable fluorescence: FIRe (ΦFIRe) and dual pulse amplitude modulated fluorescence (ΦPBR). These analyses were performed under both nutrient-replete and nutrient-stressed conditions. Results have shown that, when subjected to fluctuating light, the Φmax for C. gracile tended to increase for fluctuating light treatments up to a frequency of 2.00 Hz. However, no benefit of fluctuating light was evident in measures of Φave for this strain. Results of ΦFIRe did not appear to be different for the various light treatments for C. gracile, although the measurements of ΦPBR were greater when acclimated to static light and to light fluctuating 0.50 Hz and 1.00 Hz than when acclimated to the other light treatments. Every quantum yield parameter determined for P. tricornutum when subjected to fluctuating light was lower, relative to static light values. These experiments help give insight into the photosynthetic efficiency of these two strains and how they respond to various fluctuating light treatments. With this information, these, and other strains, can be manipulated to maximize their production and can be utilized on larger scales for pharmaceutical, biomedical, aquaculture, and biofuels applications.