Deja E. Best

Date of Award

Fall 2023

Document Type

Open Access Thesis


Environmental Health Sciences

First Advisor

Geoff Scott


This project aimed to identify the associations between the infection intensity and prevalence of Perkinsus marinus infection (i.e., Dermo ) in the Eastern oyster, Crassostrea virginica (Gmelin), with extrinsic environmental factors such as changes in salinity and temperature along with oyster host factors such as sex ratio. The objectives of the study were to: (1) identify significant associations between the dependent variables, P. marinus prevalence and infection intensity, in relation to salinity and water temperature which may be affected by climate change; and (2) identify any intrinsic factors related to sex (i.e., male, female, intersex, and indeterminant) that may affect P. marinus prevalence and infection intensity in adult oysters. To conduct this study, historical shellfish disease data from 1994 to 2006 in estuaries throughout South Carolina (SC) were provided by the SC Department of Natural Resources Marine Resources Research Institute relating to water quality, oyster disease, and oyster health along the SC Coast. Multiple ordinal logistic regression procedures on SAS Studio® were performed to determine the association and odds ratio of increasing salinity and temperature in relation to oyster sex, infection intensity, and prevalence. Estuarine sites throughout SC were selected for the study and were categorized based on estuarine type and tidal range including bar built (NC Border south to North Inlet – mean tidal range of 1.45 meters), moderate riverine (Winyah Bay south to the South Edisto River – mean tidal range of 1.52 meters) and high riverine (Ashepoo River South to the Georgia Border – mean tidal range of 2.14 meters) estuaries and land use (i.e., pristine or urban). After adjusting for age, location, and time in the models, results indicated that shell height (i.e., age), temperature, salinity, and the interaction of temperature and salinity were all significantly associated with the odds of an oyster having Dermo. Each of those variables were also associated with the adjusted odds of an oyster being female, except for salinity. In contrast with our hypotheses, land use and estuary type independently were not significantly associated with the adjusted odds of an oyster having Dermo or being female. To support this finding, our results also indicated that Dermo prevalence was not associated with the adjusted odds of an oyster occurring in a pristine or bar-built estuary compared to an urban or riverine estuary, respectively.


© 2024, Deja E. Best