Parasites were found in samples of bay scallops collected from the Peconic Bays after a nearly complete die-off of adult scallops here last summer, announced New York State Department of Environmental Conservation Commissioner Basil Seggos on Friday.

These coccidian parasites are now being considered a contributing factor in the die-off

Coccidian parasites are members of the Apicomplexa phylum, and bivalve shellfish (which have two shells, like scallops), typically siphon the parasites from the water column as they strain seawater during filter feeding.

Coccidian parasites are a spore-forming unicellular parasite that needs animal flesh to live and reproduce, and are commonly found in the intestinal tracts of animals, including domestic pets.

In November of 2019, the DEC arranged for disease diagnostic testing of a sample of 32 bay scallops collected from Hay Beach on Shelter Island with the help of the Marine Animal Disease Laboratory (MADL) at Stony Brook University.

The testing detected a coccidian parasite infecting the kidney of both juvenile and adult bay scallops in all samples the samples whose kidneys were examined. In some of the infected scallops, scientists also observed extensive damage of the renal tubules of the kidney, which they believe was sufficient damage to cause mortality.

The DEC is quick to point out that these parasites are not harmful to humans, but they “could significantly affect the bay scallop fishery.”

“The discovery of a protozoan parasite in bay scallops from Peconic Bays represents a significant threat to this commercially important fishery,” said Mr. Seggos. “While the parasite is not a public health concern, DEC is working with Stony Brook’s Marine Animal Disease Laboratory to investigate environmental factors that promote disease development of the parasite and monitor its geographical extent in bay scallops in Peconic Bays in order to protect and restore this ecologically and economically important resource.”

New York’s bay scallops are primarily located in the waters of the Peconic and Gardiners bays. Bay scallop landings reported in 2017 and 2018 exceeded 108,000 pounds, with a dockside value of $1.6 million.

During the summer of 2019, there was a catastrophic die-off of adult bay scallops in the Peconic Bays, with estimates of more than 90 percent mortality of adult bay scallops throughout the Peconics. In some areas, there was 100 percent mortality of adult scallops.

Scientists working on scallop restoration efforts have theorized the deaths were due to physiological stress while the scallops were spawning, which was exacerbated by high water temperatures (mid-80s) and low dissolved oxygen.

Juvenile scallops were not impacted.

This parasite is now considered a contributing cause of the die-off, but the DEC says that “further research is needed to determine the life cycle, rate of infection, transmission, geographical distribution and environmental requirements of the parasite.”

On December 6 of last year, Governor Andrew Cuomo issued a letter to U.S. Commerce Secretary Wilbur Ross requesting a federal fishery disaster declaration for the bay scallop fishery. 

The DEC is still working directly with National Oceanic and Atmospheric Administration Fisheries to provide additional information to support the disaster determination.

Beth Young
Beth Young is an award-winning local journalist who has been covering the East End since the 1990s. She began her career at the Sag Harbor Express and, after receiving her Masters from the Columbia University Graduate School of Journalism, has reported for the Southampton Press, the East Hampton Press and the Times/Review Media Group. She founded the East End Beacon website in 2013, and a print edition in 2017. Beth was born and raised on the North Fork. In her spare time, she tinkers with bicycles, tries not to drown in the Peconic Bay and hopes to grow the perfect tomato. You can send her a message at

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