Survey Investigates Possible Threat to Maine Oysters

A delicacy sought by locals and visiting seafood connoisseurs alike, Maine oysters are essential to the state’s culture and economy. Tourists flock to the coast each summer to dine at raw bars and attend festivals celebrating their briny meat, and oyster exports comprise a burgeoning sector of the state’s economy. New research by several Bigelow Laboratory scientists identifies potential sources of disease for Maine oysters, providing shellfish growers important information needed to protect against threats.

“Oyster aquaculture is a thriving industry that is only growing stronger, but Maine is not immune to oyster disease,” said Senior Research Scientist José Antonio Fernández Robledo. “In order to be best equipped to grow shellfish, it’s important to have a baseline of information about the parasites that could infect them.”

Several years ago, Fernández Robledo secured funding from the NOAA Saltonstall-Kennedy Foundation and set out to provide that critical baseline. In 2016 and 2017, he led the largest-ever survey of oysters in Maine. He teamed up with Senior Research Scientists Pete Countway and Nick Record, as well as Nick Marquis and Theodore Bishop, former Research Experience for Undergraduate students at Bigelow Laboratory.

Working with aquaculturists, the research team sampled oysters grown along Maine’s coast and used a DNA-based technique to detect potential parasites. They also assessed other single-celled organisms in the local water, painting a portrait of the environment and the species present – including three pathogens known to infect oysters, and two pathogens that oysters can concentrate as they filter seawater.

Single-celled parasites are one of the main threats to aquaculture programs around the world. Despite excellent growing conditions, Maine farmers saw devastating oyster die-offs in the 1990s, and again in 2010. These events were blamed on the parasite Haplosporidium nelsoni, popularly known as MSX.

“In order to support this industry, we need to be proactive about conducting research rather than just responding to problems that arise,” Fernández Robledo said. “Comprehensive and sustained surveys are fundamental for making informed decisions, and for understanding what has happened if a die-off does occur.”

The researchers are also working to develop fast and affordable tests that farmers can run on-site to look for pathogens themselves. They are collaborating with scientists at the Gloucester Marine Genomics Institute, which has developed related tests based on the molecular tool CRISPR/Cas 9. This type of monitoring approach can help growers anticipate and respond proactively to prevent the spread of shellfish diseases.

“Understanding the diversity of parasites in the water and the genetic signatures they leave in shellfish is a crucial step to help us understand the sources and timing of infections,” said Senior Research Scientist Pete Countway. “We can use that information to empower growers and equip this industry with the tools it needs.”

This research can have even broader applications as well. Farmers who want to selectively breed their stocks for resistance to parasites can use it to guide those efforts, and it may also inform research into exactly how these organisms impact oysters and interact with the ecosystem.

“This research is creating valuable tools to understand and protect our coastal resources,” Fernández Robledo said. “Personally, I love eating oysters, and I'm excited that what we're learning can be used to support this important Maine industry.”