Date of Award


Document Type

Campus Access Dissertation

Degree Name

Doctor of Philosophy (PhD)


Biology/Environmental Biology

First Advisor

Michael P. Shiaris

Second Advisor

Douglas Woodhams

Third Advisor

Michael F. Tlusty


The Eastern oyster (Crassostrea virginica) is an important aquaculture product in the Eastern U.S., comprising a $50 million industry in Massachusetts alone. In addition to economic value, oysters provide well-documented ecosystem services, improving coastal water quality and increasing seagrass community biodiversity. Bivalve microbiomes play important roles in both host health and human disease transmission. Oyster microbiome structure and stability are affected by many abiotic factors, but of particular concern are the predicted effects of climate change, namely, increased water temperature and reduced salinity. These changes are expected to alter marine bacterial populations, including the proliferation of vibrios. While most vibrios are considered harmless coastal marine inhabitants, several species are of human health concern. Of these, Vibrio parahaemolyticus currently poses the largest foodborne illness risk due to consumption of raw and undercooked oysters. In this dissertation, I investigated the influence of abiotic factors on the Eastern oyster (Crassostrea virginica) microbiome, and on prevalence and diversity of oyster-associated Vibrio species, with focus on V. parahaemolyticus. Using both next-generation sequencing and culture-based approaches, I (1) examined the core microbiome of juvenile and adult oysters, (2) tested the effect of location, temperature, and salinity on oyster microbiomes and Vibrio presence, (3) investigated oyster-associated Vibrio community dynamics over time, and (4) explored strain-level V. parahaemolyticus diversity in oysters and their environment. My research showed that oyster microbiomes change with season and age, but remain distinct from the surrounding water and sediment microbiomes. Perturbation by temperature, salinity and opportunistic colonization disrupts the oyster microbiome so post-disturbance core bacterial communities no longer bear resemblance to initial assemblages. However, predicted functional pathways are conserved despite microbiome taxonomic changes, suggesting that function may be more important than taxonomy when assessing the role of core microbiota. Vibrio populations in oysters are dynamic and communities are shaped by interspecific competition. Patterns of both marine V. splendidus-clade species detection and strain-level V. parahaemolyticus diversity suggest that oyster-associated vibrios are specialized for survival in a bivalve host. Collectively, this work improves our understanding of the C. virginica microbiome and the ecology of Vibrio species in both oysters and their growing environment.


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