Date of Award
1-1-2019
Document Type
Thesis
Degree Name
M.S. in Biological Science
First Advisor
Deborah J. Gochfeld
Second Advisor
Deborah J. Gochfeld
Third Advisor
Marc Slattery
School
University of Mississippi
Relational Format
dissertation/thesis
Abstract
Oysters are vital to the health of estuarine ecosystems and provide critical ecosystem services, such as water quality improvement, nursery habitat for commercially important fisheries, and shoreline stabilization. Despite their ecological and economic importance, oyster reefs are exposed to many stressors, and oyster populations in Mississippi have declined dramatically in recent years. The present study focuses on the effects of hypoxia and tributyltin (TBT) on the Eastern oyster, Crassostrea virginica. Hypoxic events are increasingly comin coastal ecosystems worldwide, and TBT is a legacy toxicant once used as an antifoulant. The effects of these stressors were assessed on adult oysters deployed in the Mississippi Sound, where they experienced a natural hypoxic event, and in the laboratory, where oysters were exposed to either hypoxia or TBT alone or to a combination of the stressors (hypoxia+TBT). Effects were quantified through the measurement of mRNA expression of HIF1-α as a marker of hypoxic stress, Tβ-4 to evaluate immunosuppression, and CvPPAR-δ to assess its expression after TBT exposure. Physiological parameters, including hemocyte counts, clearance rates, and oxygen consumption rates, were measured to evaluate how these stressors impact important life sustaining functions. Exposure to a natural hypoxic event for nine days up-regulated mRNA expression of HIF1-α and Tβ-4, while CvPPAR-δ was significantly down-regulated and no effects on physiological parameters were observed. In the lab, oysters exposed to both hypoxia alone and hypoxia+TBT shosignificant up-regulation of HIF1- α and down-regulation of Tβ-4 mRNA expression on days 8 and 12, however, physiological functions were relatively unaffected. CvPPAR-δ mRNA expression was down-regulated under exposure to TBT, hypoxia, and the combined treatments, indicating that this nuclear receptor pathway is responsive to these stressors. Findings from the study indicate potential for immunosuppression as a result of combined stressors, which could increase oyster vulnerability to pathogens. Additionally, a field study was performed during April-September 2019 to assess the effects of an extremely low salinity event due to dual openings of the Bonnet Carré Spillway (BCS) on oyster mortality. Two months following the second closing of the BCS, oyster mortality was 100% at five oyster reefs in the Mississippi Sound.
Recommended Citation
Barnett, Ann Fairly, "The Independent And Combined Effects Of Hypoxia And Tributyltin On The Eastern Oyster, Crassostrea Virginica" (2019). Electronic Theses and Dissertations. 1915.
https://egrove.olemiss.edu/etd/1915