As the Gulf of Maine warms, characterizing seasonal baseline levels of the human pathogen Vibrio parahaemolyticus (Vp) in Eastern oysters (Crassostrea virginica) is crucial, along with synoptic environmental data, to develop predictive capacity and risk management strategies. In Maine, USA, from May to November 2023, oyster samples were collected from Scarborough River, Maquoit Bay, and the Damariscotta River. Vp was quantified using the U.S. Food and Drug Administration-approved three-tube most-probable-number (MPN) real-time PCR method, detecting the presence of total Vp (i.e., tlh gene) and potentially pathogenic Vp (i.e., tdh and/or trh genes). tlh was detected at all sites once water temperatures reached 16°C, with densities ranging from <3 to >1,100 MPN g-1. Generalized additive models revealed significant positive relationships between both potential pathogenic markers (tdh and trh) and sea surface temperature. tdh in the Damariscotta River, the largest oyster-growing area in northern New England, was the most responsive to water temperature, and trh in Maquoit Bay was the most responsive to salinity. Statewide Vp regulations for harvesting and handling oysters were implemented in Maine in 2024, and these baseline data already demonstrate the importance of maintaining cold chain storage, as potentially pathogenic strains were detected at all three sites. Given the growing number of Vp-associated illnesses and the clear response of Vp to warming conditions in the region, these baseline data provide timely insights for harvesters and inform policies to safeguard public health.IMPORTANCEThe Gulf of Maine is both a hotspot for expanding aquaculture production and one of the fastest warming marine regions in the world. Rising numbers of vibriosis illnesses in warmer months associated with consumption of raw oysters, including Maine's first outbreak in 2023, highlight critical gaps in baseline data on the human pathogen Vibrio parahaemolyticus (Vp) (State of Maine, Department of Marine Resources, Vibrio parahaemolyticus control plan, chapter 115.02.a, 2016). The state of Maine requires up-to-date baseline information on Vp in productive growing areas to respond effectively to future illnesses and potential growing area closures. Our results support the need for a statewide Vp control plan that addresses harvest and post-harvest practices, particularly minimizing temperature abuse of live oysters. As climate change continues to warm coastal waters and alter estuarine conditions, systematic data on Vp abundance and seasonality are increasingly essential for managing the public health dimensions of shellfish aquaculture in Maine and similar high-latitude regions.
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