Electronic Theses and Dissertations

Date of Award


Document Type


Degree Name

M.S. in Biological Science



First Advisor

Clifford A. Ochs

Second Advisor

Michael Mossing

Third Advisor

Marjorie M. Holland

Relational Format



The marine microalgae Nannochloropsis spp. are of both ecological and economic importance as they contribute to the base of the food chain of marine systems, and can accumulate a considerable amount of lipids. Their lipids can be grouped into two categories, storage lipids, which are mainly triglycerides (TGs), and structural lipids, which are composed of polyunsaturated fatty acids (PUFAs). PUFAs are essential nutrients for both aquatic animals and humans, while TGs can be transesterified to produce biodiesel. Lipid formation in microalgae depends on several environmental factors and Nannochloropsis spp. have been shown to accumulate excess storage lipids under stressful conditions. Changes in either TGs or PUFAs in response to environmental factors is therefore of economic and ecological concern. The objectives of this project were (1) to determine the effect of UV-A (320 - 400 nm), a potential environmental stress factor, on total lipid accumulation in Nannochloropsis oculata, (2) to examine if there is reciprocity in the relationship of exposure duration to exposure irradiance on the stress response; and (3) to study the interactive effect of UV-A and nutrient concentration on lipid accumulation in N.oculata. The first and second objectives were addressed using a series of 7-day bioassay experiments, in which N.oculata cells were exposed to three UV-A irradiances (I), 6, 12, and 24 W m-2. For each irradiance there were three different durations of exposure (T) such that they resulted in three Doses (I x T); 24, 48 and 72 J m-2. If the same doses have a similar effect, irrespective of UV-A irradiance and duration of exposure, reciprocity holds. Lipid analysis was done using the lipid soluble fluorescent dye Nile Red. UV-A treatments significantly increased the chlorophyll-specific lipid concentration of N.oculata cells, and I was unable to reject that reciprocity holds. The third objective was addressed by a pair of factorial bioassay experiments. There was a synergistic effect of UV-A exposure and nutrient depletion on lipid content of N.oculata cells.

Included in

Biology Commons



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