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The Effects Of Hypoxia And Freshwater Intrusion On The Eastern Oyster (Crassostrea Virginica), James Henry Gledhill

Electronic Theses and Dissertations

Recent estimates revealed a significant decrease in oyster populations worldwide. This drastic decrease has detrimental effects on coastal and estuarine ecosystems. Two environmental stressors that are thought to be contributing to the oyster population decline are hypoxia and excess freshwater intrusion. In this study, effects of hypoxia and low salinity on oysters were investigated using a combination of laboratory and field-based methods. In the laboratory, oysters were exposed to 2, 4, or 8 days of hypoxia (< 2 mg/L dissolved oxygen) folloby 6 days of recovery in normoxic conditions. At the same time, caged oysters were exposed to a naturally occurring hypoxic event in the field. After 8 days, laboratory-exposed oysters shoevidence of immunosuppression indicated by significant downregulation of the immune-related gene thymosin-β4 (Tβ-4) and a significant decrease in total circulating hemocytes compared to controls. However, in field oysters exposed to a naturally occurring hypoxic event, no effect on total hemocyte counts and an upregulation of Tβ-4 was observed. In a second field study, to investigate how oysters respond to prolonged freshwater exposure, caged oysters were placed on 23 April 2019 at six reef sites in the Mississippi Sound along with in situ water quality sensors. One-hundred percent mortality of caged oysters occurred at four of the six sites. Of the 6 six sites, Henderson Point Reef and Kittiwake Reef shosome caged oyster survival. At Henderson Point, where higher mortality was observed compared to Kittiwake, a significant increase in lipid peroxidation was detected. Analysis of mRNA expression of surviving caged and native oysters revealed downregulation of genes involved in immune function, low oxygen response, and osmoregulation. These results show possible evidence of energetic depression which inhibits adequate adaptation to low salinity conditions. Energetic depression and increased oxidative damage could have contributed to higher oyster mortality. Dredge sampling of native oysters at the all Mississippi Sound field sites on 27 September 2019, following recovery to ~15 ppt salinity, still indicated 100% native oyster mortality due to the prior prolonged freshwater exposure. Continued monitoring of western Mississippi Sound oyster reefs is crucial to observe recovery of oyster populations.

Application And Refinement Of Molecular Ecology Techniques For Amphibian Conservation, Stephanie Marie Burgess

Electronic Theses and Dissertations

Wildlife conservation has become increasingly difficult due to habitat loss habitat fragmentation and land use change. Thus conservationists have embraced advances in molecular ecology such as landscape genetics and microbial bioinformatics that employ genetic techniques to further understand the relationship between individuals and their environment. In landscape genetics model inferences can be used to identify features that facilitate or resist gene flow providing a framework for anticipating the impacts of land use changes on a species’ ability to disperse. However the factors that affect the transferability of landscape genetics inferences are poorly understood and little is known about the effect …

Location, Location: Factors Influencing Greenhouse Gas Fluxes From The Mississippi Delta Agricultural Region, Michael P. Keating

Electronic Theses and Dissertations

Methane (CH4), nitrous oxide (N2O), and carbon dioxide (CO2) fluxes from agricultural landscapes may contribute significantly to regional greenhouse gas budgets due to stimulation of soil microbial activity through fertilizer application. Few studies have made measurements of CH4, N2O, and CO2 from the dominant landscape features of the agricultural landscape: farmland, riparian zone, and wetland habitat. This study assessed gas emission variability from the Mississippi Delta agricultural landscape and explored the effects of hydrology and hydrophytic vegetation on gas emissions.

Gas collection chambers were utilized to make gas measurements from soybean and corn farmland, vegetated riparian buffer, and two vegetated …

Temporal And Spatial Assessment Of Pahs In Water, Sediment, And Oysters As A Result Of The Deepwater Horizon Oil Spill, Meghan Christina Dailey

Electronic Theses and Dissertations

On April 20, 2010, BP's Deepwater Horizon oil rig exploded leaking over 200 million gallons of crude oil into the Gulf of Mexico for 84 days. Exposure to oil-associated polycyclic aromatic hydrocarbons (PAHs) in the water and sediment could severely impact the aquatic organisms inhabiting the Gulf of Mexico (i.e. developmental defects, reproductive effects, death, etc.). Therefore, water, sediment and oyster, Crassostrea virginica, samples were collected approximately bimonthly between May 26 and November 30, 2010 from multiple sites along the Gulf Coast, namely, two sites in Mobile Bay (Denton and Sand Reefs at 1 or 0.1 m above the bay …

Stochastic Models For Evolutionary Genetic Problems, Wei Liao

Electronic Theses and Dissertations

Two stochastic models are designed for answering evolutionary genetic problems. The first study shows that inbreeding-environment interactions increase extinction risk. The second research demonstrates that 1) the carrying capacity and initial population growth rate is critical to determine the population persistence time; 2) increasing the advantageous mutation rate reduces the extinction risk although its effects are usually shadoby population size and fitness; 3) the new mutation correlation among environments rises during the evolution process, but it has compromised effects on population fate. Being able to accurately estimate the persistence time of populations of endangered plants and animals is central to …