Shellfish farmers in New Hampshire need access to genetically diverse shellfish seed to sustain their businesses, but they also must guard against harmful bacteria like Vibrio. Concerns about human illness associated with Vibrio strains have led state officials to restrict where shellfish seed can be imported from. While these policies help protect public health, they’ve also limited seed availability and genetic diversity of farmed shellfish. There is also a limited understanding of Vibrio association with clams and scallops, which are not typically consumed raw and pose less of a threat to consumers, but could still be a source of environmental Vibrio contamination.
This research project by Cheryl Whistler, Professor of Molecular, Cellular, and Biomedical Sciences at the University of New Hampshire, aims to expand access to safe shellfish seed by better understanding and reducing Vibrio risks. Building on previous Sea Grant-funded research, the project will test how factors like breeding practices, hatchery conditions, and pre-deployment treatments (such as salinity changes) influence the presence of Vibrio in oysters and other shellfish. The project will develop improved tools to detect harmful strains, including a new method for identifying an emerging pathogen, Vibrio fluvialis. Ultimately, the goal of this work is to provide farmers and regulators with the science needed to safely broaden seed sourcing options, while also creating clear, accessible resources that explain how these practices protect both public health and the shellfish industry.
Principle Investigator
Cheryl Whistler, Ph.D.
Professor, Department of Molecular, Cellular, and Biomedical Sciences, University of New Hampshire
Project Funding Cycle
2026-2027 NH Sea Grant Biennial Research Funding
Project Abstract
Vibrio is a dirty word to growers and consumers of shellfish alike, but an unavoidable reality. The reliance on importation of shellfish seed has created significant challenges for the New Hampshire (NH) shellfish aquaculture industry in growing their crops and businesses while avoiding the fate of some in other regions that are plagued by local source human Vibrio illnesses. Illnesses associated with regional product have become more of a concern in the Northeast due to persistence of hypervirulent pathogens, particularly a V. parahaemolyticus strain from the Pacific called ST36 in some areas to the south of NH. NH State public health officials and shellfish managers implemented a policy in 2018 restricting importation of seed from localities with a history of illness, targeting prevention of introduction of mostly Vibrio parahaemolyticus, but other Vibrio pathogens have also become a concern for seed contamination and importation, including Vibrio vulnificus, and an emergent pathogen, Vibrio fluvialis, that also causes gastroenteritis. Unfortunately, this policy has strained NH shellfish farmers due to limited availability of genetically diverse seed. Currently, oyster seed is most often acquired from hatcheries in Maine, now managed by a single entity which will likely further reduce the genetic variation available. Though other, larger seed is sometimes permitted on a case-by-case basis from localities without a history of disease, establishing the lack of risk prior to permitting is yet another challenge. Farmers who want to diversify their production to include scallops and clams also face challenges, because there is little understanding of Vibrio association with other shellfish that is less typically consumed raw and whole since they pose little risk to consumers but could still be a source for environmental contamination. Here, we will apply the methodologies and knowledge developed in our ongoing Sea Grant project which seeks to evaluate and optimize on-shore salinity relay for Vibrio parahaemolyticus and Vibrio vulnificus reduction, to evaluate risk associated with genetically diverse shellfish seed from a wider distribution, capturing different genetic stocks of oysters (Crassostrea virginica) and other shellfish seed as available (e.g. Argopecten irradians, Placopecten magellenicus, Merceneria merceneria) with the goal of generating fundamental knowledge to potentially expand seed access. Specifically, we will focus on how the flexible genome of the oyster microbiota is shaped by breeding programs that select for different oyster features than Vibrio accumulation, as well as different hatchery and nursery operations, as well as pre-deployment salinity relay. We will continue with ongoing development of sensitive assays for detecting Vibrio strains of most concern in assays and protocols specific to and optimized for shellfish seed, and generate a new assay for enumerating V. fluvialis for which there is currently no qPCR-based MPN procedure. To enhance our outreach, we will work with Sea Grant extension and communication staff to produce public-accessible materials that explain the many processes in place to protect consumers, as well as technical reports distilling the key practices that reduce risk and provide summary data to inform adaptive management decisions within and beyond our region.
