Date of Award
12-1-2025
Document Type
Thesis
Degree Name
Master of Science in Coastal Marine and Wetland Studies
Department
Coastal and Marine Systems Science
College
College of Science
First Advisor
Juliana M. Harding
Second Advisor
Erin J. Burge
Third Advisor
John J. Hutchens
Additional Advisors
Scott L. Parker
Abstract
Eastern oysters (Crassostrea virginica) are estuarine ecosystem engineers that create complex habitats that support marine life and stabilize shorelines. Oysters are sequential protandric hermaphrodites where small males transition to intermediate hermaphrodites and larger females as growth occurs. Data were collected in North Inlet estuary, South Carolina to examine how oyster life history traits and host-parasite interactions shape population dynamics during the 2022 spawning season. Chapter 1 evaluated monthly trends in oyster density, sex ratio, sex-at-length, and biomass relationships from May–October 2022. Population density declined from 680±1.1 oysters m⁻² in May to 230±0.6 oysters m⁻² in October, however mean shell length increased. Even male:functional female sex ratios in May became male dominated June–October. Sex-at-length transition increased from 61 mm in May to 80 mm in October. Functional females contributed more biomass early in the spawning season, whereas males dominated biomass later in summer and fall. These findings indicate how fast growth and constant recruitment support oyster populations with environmental stressors such as high water temperature. Chapter 2 compared two quantitative methods used to estimate Perkinsus marinus infections in Eastern oysters. Hypnospores were counted in mantle tissue after Ray’s fluid thioglycollate incubation (field of view method) and in a clear suspension after oyster tissue was dissolved (sodium hydroxide digestion method). Infection densities obtained from the digestion method were significantly higher than those from the field of view method. A regression model was developed to accurately estimate infection density for the field of view method to improve precision. Although the digestion method was more sensitive at low infection densities, both methods produced comparable weight-standardized estimates for highly infected samples and assigned similar Mackin score values for over 80% of tissues. These results provide an efficient and accurate framework for quantifying Perkinsus marinus infection intensity in ecological studies. Chapter 3 assessed seasonal patterns of Perkinsus marinus infection intensity and prevalence in relation to oyster sex, length, biomass, and environmental conditions in Clambank Creek. Mean water temperatures and salinities ranged from 20–30°C and 30–36 psu across the sampling period. Mean infection intensity remained low (< 1.5 on the Mackin scale) yet increased in both sexes from early to late season. Fewer than 10% of oysters exhibited severe infections (Mackin >3). Monthly prevalence exceeded 80% for both sexes, peaking at 100% for females in August and 98% for males in October. Weighted prevalence remained consistently low (< 1.5), indicating chronic but sublethal infections. These patterns suggest a long-term coexistence between host condition and parasite proliferation under seasonal high temperature in the summer and fall and relatively consistent high salinity conditions.
Recommended Citation
Slaughter, Caroline, "Linking seasonal Eastern oyster (Crassostrea virginica) population structure and Perkinsus marinus infection in a South Carolina estuary" (2025). Electronic Theses and Dissertations. 227.
https://digitalcommons.coastal.edu/etd/227