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Oysters play an important role in coastal ecology and are a globally popular seafood source. However, their filter-feeding lifestyle enables coastal pathogens, toxins, and pollutants to accumulate in their tissues, potentially endangering human health. While pathogen concentrations in coastal waters are often linked to environmental conditions and runoff events, these do not always correlate with pathogen concentrations in oysters. Additional factors related to the microbial ecology of pathogenic bacteria and their relationship with oyster hosts likely play a role in accumulation but are poorly understood. In this study, we investigated whether microbial communities in water and oysters were linked to accumulation of Vibrio parahaemolyticus, Vibrio vulnificus, or fecal indicator bacteria. Site-specific environmental conditions significantly influenced microbial communities and potential pathogen concentrations in water. Oyster microbial communities, however, exhibited less variability in microbial community diversity and accumulation of target bacteria overall and were less impacted by environmental differences between sites. Instead, changes in specific microbial taxa in oyster and water samples, particularly in oyster digestive glands, were linked to elevated levels of potential pathogens. For example, increased levels of V. parahaemolyticus were associated with higher relative abundances of cyanobacteria, which could represent an environmental vector for Vibrio spp. transport, and with decreased relative abundance of Mycoplasma and other key members of the oyster digestive gland microbiota. These findings suggest that host and microbial factors, in addition to environmental variables, may influence pathogen accumulation in oysters. 

Oysters are an integral part of many marine ecosystems. They provide food for several species of snails and crabs and act as natural water filters, preventing algal blooms and nutrient-induced oxygen depletion in aquatic ecosystems (eutrophication). Additionally, oyster reefs provide a habitat for several small fish and crustacean species. Lastly, they promote underwater vegetation growth, providing greater coastal resistance to erosion and protection against storms. In recognition of the significance of oysters in promoting marine biodiversity, countries such as the United States and Australia have invested millions of dollars in the restoration of oyster reefs along the Pacific, Atlantic, and In¬dian ocean coasts. A meta-analysis was conducted by combining data from multiple studies as by doing so it is often possible to identify more reliable trends than by comparing the results of individual analyses. We utilized the open-source microbial analysis platform Qiita to gain new insight into Pacific Oyster microbiomes and to generate a tool for the scientific community, enabling future studies of new testable hypotheses. After reading papers utilized in the meta-analysis, we hypothesize that bacteria belonging to the Mycoplasmataceae and Spirochaetes family will be common dominant taxa across all geographic regions. Several papers have attributed oyster microbiome fluctuations to environmental changes. These studies found that some tissue types are more affected than others, particularly finding that gut taxonomic evenness and abundance varied the most by tissue type. Therefore, we also hypothesize that the core microbiome, particularly that of the gut, would be very small. A small core microbiome suggests a significant level of variation in taxonomic abundance and diversity for a given tissue type between samples.