Date of Award

5-2013

Degree Type

Masters Thesis

Degree Name

Master of Science (MS)

Committee Chair

Robert Griffitt

Committee Chair Department

Coastal Sciences, Gulf Coast Research Laboratory

Committee Member 2

Chet Rakocinski

Committee Member 2 Department

Coastal Sciences, Gulf Coast Research Laboratory

Committee Member 3

Robin Overstreet

Committee Member 3 Department

Coastal Sciences, Gulf Coast Research Laboratory

Abstract

My thesis research focused on the effects of two environmental stressors on the small estuarine fish, Sheepshead minnow (Cyprinodon variegatus). Specifically, I examined the effects of exposure to crude and dispersed oil and hypoxia. I looked for responses using a combination of molecular and ecological endpoints. These stressors were chosen because of the 2010 Deepwater Horizon oil spill which released 4.1 million barrels of crude oil into the northern Gulf of Mexico. An estimated 2.1 million gallons of Corexit 9500 was used in an attempt to disperse the oil slick into the water column. The spill happened in a time and region that is also chronically affected by hypoxia.

Previous research has indicated that there may be an interaction between the molecular pathways Sheepshead minnow use to respond or defend against both hydrocarbon and hypoxia stress (specifically that Aryl hydrocarbon Receptor Nuclear Translocator (ARNT) and Hypoxia Inducible Factor 1β (HIF-1β) are hypothesized to be the same protein). Furthermore, much of the research using hydrocarbon exposure on estuarine fish has ignored this potentially critical interaction. Therefore, I focused my thesis research on explaining the effects co-exposure to ecologically relevant levels of crude (non-dispersed) and dispersed (with Corexit 9500) oil and hypoxia could have on the environment.

My results indicate that Cytochrome P450 1A (CYP1A) increases in a dose dependent manner when larval and adult C. variegatus are exposed to crude (WAF) and dispersed crude (CEWAF) oil. Vascular Endothelial Growth Factor (VEGF) expression increases in a dose dependent manner when larval C. variegatus are exposed to 2.5 mg/L dissolved oxygen (DO) levels. Also, a synergistic effect is observed on CYP1A expression when co-exposure to WAF + hypoxia, CEWAF + hypoxia occurs. Finally, along with an increase in adult mortality when co-exposed to WAF/CEWAF and hypoxia, I observed a decrease in egg production, egg hatch success and larval survival when hypoxia and co-exposure occurs. A significant difference was observed between the egg production within WAF/CEWAF + hypoxia exposed adults and the adults exposed to control treatments (hypoxia - P<0.05, hypoxia WAF - P<0.05, and hypoxia CEWAF - P<0.05). In addition, a significant difference was observed in egg hatch success between WAF/CEWAF + hypoxia exposed eggs and control treatment exposed eggs as well as eggs that were continuously exposed to the hypoxic treatment (hypoxia treatment - P<0.001, hypoxia WAF CTRL and TRT - P<0.001, hypoxia CEWAF CTRL and TRT - P<0.001). My research shows a significant impact on reproductive success during simultaneous exposure to WAF/CEWAF and hypoxia; this indicates the importance of taking environmental parameters such as hypoxia into consideration when evaluating the impact of an oil spill.

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