Doctor of Philosophy (PhD)


Oceanography and Coastal Sciences

Document Type



The Deepwater Horizon oil spill in the Gulf of Mexico (GoM) raised an important question. What is the ecological impact of the oil, the dispersant, and the dispersed oil to the GoM ecosystem? Significant and varying research efforts have contributed answers to this question. However, to better understand the complete ecological consequences of the spill in the GoM, the impact of the spill at the base of marine food web should be examined. This research aims to understand impact of the spilled oil, South Louisiana crude oil (LSC), the chemical dispersant, Corexit® EC9500A, and the dispersed oil on phytoplankton communities in the GoM at individual, community, toxin-production, enzymatic, and gene-expression levels. At the individual level, phytoplankton size influenced tolerance to crude oil, but taxonomic group seemed to be a more predominant criterion. In general, diatoms showed better tolerance to crude oil than dinoflagellates. Naphthalene and benzo(a)pyrene cannot be solely used as surrogates to assess crude oil toxicity on phytoplankton. Community-level effects were investigated under oligotrophic and eutrophic conditions. Diatoms showed the greatest tolerance to crude oil exposures under every condition that was assessed. Nevertheless, different diatom groups had distinct responses under different nutrient regimes. The amount of nutrients greatly influences phytoplankton response during crude oil exposure. Crude oil also affects toxin production of two ecologically important toxic phytoplankton species of the GoM, Karenia brevis and Prorocentrum minimum. It was revealed that reactive oxygen species are activated in phytoplankton exposed to crude oil. Phytoplankton species also displayed signs of oxidative stress and damage in their lipid structure under crude oil exposure. A gene expression study indicated that crude oil does not cause significant difference in the expression levels of selected genes between the control group and samples treated with crude oil. This research provides essential data for impact assessment of oil spills and pollution on phytoplankton ecology and bloom dynamics in the GoM. These datasets contribute substantially to existing scientific knowledge about the region and provide baseline information for subsequent research efforts that seek to further understand the impact of oil on the marine planktonic ecosystem in the GoM.



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Committee Chair

Bargu Ates, Sibel