Rising Ocean Temperatures Put New England Oyster Industry in Hot Water

Wednesday, October 2, 2013
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In the wake of recent, unprecedented shellfish bed closures in Massachusetts and Connecticut, three scientists at the University of New Hampshire (UNH) have been analyzing the bacterial strains responsible for the illnesses, fielding phone calls and emails from the press, and preparing to speak at shellfish industry meetings. Professors in UNH’s College of Life Sciences and Agriculture (COLSA) Cheryl Whistler, Vaughn Cooper, and Steve Jones have overlapping expertise in the study of pathogenic Vibrio parahaemolyticus – the bacterium that sickened people who ate oysters from the contaminated beds in the summers of 2012 and 2013. Unlike with recurrent outbreaks in Washington State and the Gulf of Mexico, the presence of pathogenic Vibrio parahaemolyticus is rare in the Northeast as cooler water temperatures protect against bacterial growth. But with the regions’ rise in ocean temperatures and unusually heavy, intermittent rainstorms, conditions have changed over time, generating a host of problems that impact people’s health and the economy.

The Center for Disease Control reports a 43% increase in pathogenic Vibrio parahaemolyticus in 2012, with 142 cases not diagnosed for each case reported. In the same family as the bacterium that causes cholera, Vibrio parahaemolyticus exists in brackish saltwater and thrives during the summer months when water temperatures increase. It is known to enter the body through ingestion or exposure to wounds, but severe disease is relatively uncommon. Within 24 hours of infection, pathogenic Vibrio parahaemolyticus typically causes watery diarrhea along with nausea, fever, and chills that last three days on average. Such illness can be completely prevented by cooking the shellfish in which Vibrio parahaemolyticus is present and care in preventing cross-contamination as with all uncooked foods.

In the 1980s, scientists at UNH were the first to detect Vibrio vulnificus – a potentially more serious species of Vibrios– north of Long Island Sound. Since then Vibrios have been studied throughout the shellfish and waters of the Great Bay estuary, which provides an ideal environmental laboratory with its gradients of salinity, contamination and nutrients, and suspended solids. “We saw that if you moved oysters with Vibrios from areas that have medium-level salinity to areas that have higher salinity, the Vibrios disappear,” says Research Associate Professor of Natural Resources and the Environment Steve Jones of his team’s discovery that has had great significance to the shellfish industry. “It’s not a physical thing – like salinity as the mechanism that causes the Vibrios to disappear – it’s more of a biological factor. When you move oysters from a lower salinity environment to one with higher salinity, it’s the microorganisms that are present that are probably causing the Vibrios to disappear,” says Jones. This speculation has spurred important research, which has been supported by the New Hampshire Agricultural Experiment Station (NHAES) in recent years even when other funding fluctuated due to the fact that there were only rare reports of people becoming sick from eating oysters harvested in northeastern waters. Jon Wraith, Dean of COLSA and Director of the NHAES, notes that “this represents a ‘poster-child’ example for why is it imperative that we support a strong research program spanning the range from solving immediate issues to developing fundamental knowledge about the systems that are important to us.  At some point the information we derive from what is often termed ‘basic research’ becomes critical to solving new problems as they arise.  In those cases, we can’t afford to wait to begin new efforts to answer these questions.”

Ashley Marcinkiewickz, Ph.D. student in Microbiology

Ashley Marcinkiewicz, Ph.D. student in Microbiology

“We as much as called this back in 2006,” says Associate Professor of Molecular, Cellular, and Biomedical Sciences Vaughn Cooper, knowing that it was only a matter of time before changing climate conditions would present the bacterium with an opportunity to flourish. Cooper’s expertise is in understanding the genetic relationships among individuals in a population, which positions him uniquely to ask the pressing question of whether the emerging pathogenic Vibrio parahaemolyticus is from the native waters or an invasive strain. “We can use the Great Bay, which is very heterogeneous, to understand processes that are more broadly relevant,” says Cooper. “This goes beyond shellfish and food safety as a general model of climate change. The emergence of pathogenic Vibrios is just one of the many types of infectious risks that are going to increase with global warming.”

The Department of Public Health in Massachusetts sent Associate Professor of Molecular, Cellular, and Biomedical Sciences Cheryl Whistler strains of the Vibrio pathogen, which sickened more than fifty people in the last two years and precipitated the closure of multiple beds in the Bay State, for analysis in her lab on the Durham, NH, campus. “They appear to be a unique lineage, so we really are very well positioned to ask important ecological questions about where these pathogens are coming from and why they’re emerging,” says Whistler who’s interested in exploring questions about how organisms that are similar to each other have evolved different types of associations. “I’m looking at the core genomic components that contribute to general colonization, and how very closely related organisms acquire traits to become mutualistic or pathogenic.”

In the early years of their collaboration, Cooper, Jones, and Whistler were addressing basic questions of ecology in terms of what conditions influenced which Vibrios were present in the Great Bay, when they were there, and what was their genetic population structure. “We wanted to know if the Vibrios were very related to one another or if we had a really diverse endemic population,” says Whistler.
“We’ve always had in mind that this could serve as a model for how changes in the environment might drive changes in population dynamics toward pathogens becoming more prevalent.” Today, questions abound as to what drives the emergence of endemic populations and how the population changes in response to environmental conditions. Says Whistler, “These pathogens are incredibly rare in natural populations. If you went out and collected a million Vibrio parahaemolyticus, chances are you would not even encounter one pathogenic strain and yet they accumulate enough to make people sick – and we don’t know why that happens yet.”

But, the scientists are coming closer to an understanding. “There’s definitely a seasonal influence, there’s definitely an association with salinity and temperature, but there’s no single driving force that’s causing Vibrios to be dominant or not dominant,” says Whistler. “We’re really interested in the things within the Vibrio population that drive the pathogens to be more dominant.” There have been several emergence events with one dominant pandemic-strain of pathogenic Vibrio parahaemolyticus; however, in the U.S. most infections are not caused by the pandemic clone but by local, endemic populations that emerge and re-emerge each spring. It is well documented that climate change has been a causative factor in the worldwide spread of the pandemic isolate of Vibrio parahaemolyticus, but the data is lacking to implicate global warming in the emergence of its endemic populations. “We are working to understand why pathogenic Vibrio parahaemolyticus is emerging so we can develop better predictive models for when conditions are changing in a way that requires enhanced surveillance or other protective measures before people get sick,” says Whistler. And while each state has an effective control plan that is enacted after just one reported case of infection, Whistler cautions that the science needs to be done ahead of the regulation. “There needs to be good science to inform us as to what are the conditions that cause a problem and which are the problem strains because you can have a lot of Vibrios in oysters, but if they are not pathogenic no one will get sick,” says Whistler. In fact, most of the time, eating shellfish from the Great Bay and other regional waters is completely safe. As Cooper says, “We eat them and they’re delicious.”

Caroline Ward '14, Biomedical Sciences

Caroline Ward '14, Biomedical Sciences

Over the years, Cooper, Jones, Whistler, and the undergraduate and graduate students whom they mentor have been developing important working relationships throughout the Northeast with other researchers, public health and resource agencies, state shellfish programs, and the industry at large. For example, through a close partnership with Spinney Creek Shellfish Inc. in Eliot, Maine, the researchers are uniquely positioned to help oyster farmers in the region better understand how to put a safer – and more desirable – product on the market. In addition, Cooper and Jones have joined forces with Clean Air, Cool Planet – a non-profit organization whose mission is to “accelerate the transition to sustainable communities through climate mitigation, adaptation planning, and effective climate policies” – to develop far-reaching connections that help build the basis for further collaborations on a regional scale. “This is not a New Hampshire problem,” says Jones. “This is a regional problem and the science that people have been using to understand the emergence of pathogenic Vibrios is not adequate.” The team continues to delve deeply into basic research that has immediate applications, drawing from decades of UNH studies to inform their understanding of this change over time. “We are in the right place at the right time with the right expertise,” says Whistler.

In addition to ongoing support of their research from the NHAES, the scientists have received funding from the NH Sea Grant Program, the National Institutes of Health, and have designated a portion of an NSF EPSCOR grant to further their investigation of pathogenic Vibrios. For a complementary study, Cooper and Whistler were just awarded a National Science Foundation grant to research the evolutionary processes that facilitate the association of beneficial microbes and their hosts.