Researcher ORCID Identifier


Graduation Year


Document Type

Open Access Senior Thesis

Degree Name

Bachelor of Arts


W.M. Keck Science Department

Reader 1

Dr. Shelby L. Ziegler

Reader 2

Dr. Sarah Budischak

Terms of Use & License Information

Terms of Use for work posted in Scholarship@Claremont.

Rights Information

© 2023 Sofia Markiewicz


The eastern oyster (Crassostrea virginica) is a keystone species that stabilizes sediments, cycles nutrients, filters water, and provides habitats and food for estuarine fauna. Oysters are prone to several macroparasites, including oyster pea crabs (Zaops ostreum), mud blister worms (Polydora websteri), and boring sponges (Cliona sp.). Prior research has shown that shellfish infected with blister worms and boring sponges exhibit weaker shells, are more vulnerable to damage and predation, and potentially experience reduced condition. Pea crabs may cause reduced condition, growth, and fertility in their hosts. However, the extent to which these parasites harm their hosts is still unclear. We collected oysters from 24 reefs across eight sites on Georgia’s coastline and examined them for macroparasites, then quantified the relationships between macroparasite prevalence and intensity, oyster condition, site location, and reef characteristics. We found no correlation between location and infection prevalence or intensity for any macroparasites. However, increased blister worm prevalence was correlated with low salinity and low reef rugosity. Additionally, while oyster condition varied between sites, it was not a significant predictor of individual oyster condition, indicating that a non-blister worm factor is responsible for the differences in condition across the state. The geographic and environmental factors influencing oyster macroparasite infections and their effects on oyster health have been extensively explored, but have been subject to long-term study in only a few locations in Georgia, and are critical for maintaining and restoring high-quality reef habitats. The large tidal amplitude, high tidal intensity, and exclusively intertidal oyster reefs on Georgia’s coast, which differ from the conditions at other highly researched oyster communities in the eastern United States, mean that it is crucial to conduct studies in Georgia to inform decisions about oyster populations within the state. The effects of climate change may also cause macroparasite infection patterns to shift in the future, and the ability to predict these changes accurately relies on a clear understanding of how environmental conditions affect macroparasite distribution.