Master of Science (MS)


Environmental Sciences

Document Type



This research focused on the effects of un-weathered Macondo crude oil on the growth rates and pigment ratios of phytoplankton isolated from Grand Isle, LA. The experiments involved incubating nutrient-enriched artificial media containing a range of oil concentrations up to 19.2 ppm with small aliquots of coastal water from Grand Isle and measuring the growth rates of the phytoplankton during the subsequent 10–14 days and the pigment ratios of the phytoplankton at the end of log-phase growth to determine whether the crude oil affected the growth rate of the phytoplankton and their composition in terms of pigment ratios. Pigment analysis revealed that the cultures consisted almost entirely of diatoms. Results showed that there was a significant effect on diatom growth rates from the concentration of crude oil, the month, and the interaction between oil concentrations and months. In March, April, and May, growth rates at oil concentrations from 0.1 to 0.6 ppm were about 10% higher than controls. At higher oil concentrations there was a negative correlation between oil concentrations and growth rates. The ratio of fucoxanthin to chlorophyll a was positively correlated with oil concentrations in February, March and April, the implication being that the size of the diatom photosynthetic units changed in response to the oil. There was no significant correlation between growth rates and oil concentrations in July and August, nor was there any correlation between pigment ratios and oil concentrations. The July and August phytoplankton grew roughly twice as fast as the March, and April control cultures, although the growth conditions were identical. Analysis with a mathematical model of phytoplankton growth suggested that in the presence of oil, there was a transfer of resources within the March, April, and May phytoplankton, the result being an increase in the size of their photosynthetic units and a decrease in the number of photosynthetic units in response to the presence of oil. The principal antenna pigment was fucoxanthin. The phytoplankton isolated in July and August, in contrast, appeared to be completely unaffected by the presence of oil up to a concentration of 19.2ppm.



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Committee Chair

Laws, Edward