Parasite linked to scallops die-off in Peconic Bay, DEC says

Researchers have discovered what they believe is a contributing cause of the “near-unprecedented” Peconic Bay scallop die-off of 2019: a parasite found in a sample of adult bay scallops.

This is the first time the coccidian parasite has been seen in New York waters, according state Department of Environmental Conservation commissioner Basil Seggos.

“The parasite is not harmful to humans and does not pose a public health threat but could significantly affect the bay scallop fishery,” the DEC said a press release Friday.

In November, the DEC had arranged for disease diagnostic testing to be conducted on a sample of 32 bay scallops collected from Hay Beach in Shelter Island. Working with Stony Brook University’s marine animal disease laboratory, the team detected a single-celled protozoan parasite infecting the kidneys of both juvenile and adult bay scallops in all the samples, the DEC said.

“In some of the infected scallops, extensive damage of the renal tubules of the kidney was observed,” the press release read. “The extent of the lesions identified in these heavily infected scallops is sufficient to cause mortality.”

In 2017 and 2018, reported bay scallop landings exceeded 108,000 pounds with a dockside value of $1.6 million. Last summer, however, the die-off resulted in 90% to 100% mortality in certain areas, according to the release. Scientists were not immediately aware, however, that juvenile scallops had also been affected. 

They suggested high water temperature and low dissolved oxygen levels as plausible causes affecting the spawning and death of adult scallops. In November, Steven Tettelbach, a shellfish ecologist with Cornell Cooperative Extension, described the die-off as one of the most serious the East End had seen since the mid-1980s. He spoke about how it might all be linked to climate change, as 2019 set a record for the warmest water temperatures over the last five years.

“We think that the timing of scallop reproduction, which is actually a very physiologically stressful event for scallops, may have been more aligned with the highest water temperatures,” Mr. Tettelbach said at the time. “But the water temperatures in Flanders Bay and the western part of Peconic Bay [in 2019] were over 85 degrees and that’s getting very close to the lethal limit for bay scallops.” He added then that scallops are very environmentally sensitive compared to certain other shellfish species.

His prediction was mostly confirmed Friday, with the DEC supporting the theory that physiological stress during spawning season, exacerbated by high summer water temperatures and low dissolved oxygen levels, were likely contributing causes.

The DEC is continuing work with Stony Brook’s lab “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.”

In addition to the Cornell Cooperative Extension and the Peconic Estuary Program, the DEC is also working with representatives from the National Oceanic and Atmospheric Administration to provide additional information supporting the disaster, or failure determination, and will be conducting further research “to determine the life cycle, rate of infection, transmission, geographical distribution and environmental requirements of the parasite,” according to the release.

Gov. Andrew Cuomo, as part of his 2020 State of the State address, proposed the “Restore Mother Nature” initiative, an aggressive habitat restoration and flood reduction program that would support a doubling of the state’s existing artificial reef program and similar shellfish restoration initiatives. Funding for these projects has come partly from the governor’s $3 billion environmental bond act proposal and $300 million he dedicated to the state Environmental Protection Fund.