Marine Biologist Doubts Parasite Was Only Cause of Bay Scallop Collapse, But It Was Another Factor

A parasite called “a significant threat” to the Peconic Bay scallop fishery may have been a factor in the near total collapse of the scallop population last year. EXPRESS FILE

A parasite that the New York State commissioner of environmental conservation called “a significant threat” to the Peconic Bay scallop fishery has been detected in a sample of bay scallops from Shelter Island — and may have been a factor in the near total collapse of the adult scallop population throughout the estuary last year.

A type of single-cell protozoan from a group known as coccidia, the parasite found by Stony Brook University’s Marine Animal Disease Laboratory, is not harmful to humans and poses no public health threat “but could significantly affect the bay scallop fishery,” according to a January 31 announcement from the State Department of Environmental Conservation.
Basil Seggos, the DEC commissioner, said the agency was working with the lab “to investigate environmental factors that promote disease development of the parasite and monitor its geographical extent … in order to protect and restore this ecologically and economically important resource.”

The discovery will bolster Governor Andrew Cuomo’s pending request, made in a December 6 letter to U.S. Commerce Secretary Wilbur Ross, for a declaration of disaster for the Peconic Bay scallop fishery due to the 2019 die-off, so that additional federal funding can be made available for research and recovery efforts.

Just what the discovery really means for the fishery is unclear. Marine biologist Kim Tetrault, a community aquaculture specialist with the Cornell Cooperative Extension in Southold, said he was skeptical the parasite “was the actual vector for the whole meltdown.”

Mr. Tetrault, who joined the organization in 1995 to help restore the scallop fishery after mysterious “brown tide” algae blooms had wiped it out in the 1980s, noted that bug scallops did not die off in 2019 and remain viable — the reason for his hunch that the population will bounce back this year and make for a good harvest in the coming fall.

“In general, scallops are remarkably precarious critters, and there are a lot of things that want to put them out of business,” he said in an interview. A number of factors may have been at work last summer to kill off adult scallops, including higher water temperatures, likely a symptom of climate change, that lowered oxygen levels, he agreed. But why weren’t there fish kills, too? he wondered.

DEC commissioner Basil Seggos. EXPRESS FILE

A reported invasion of cownose rays, which eat scallops, “like the parasite, I wouldn’t discount — but I doubt they were responsible for a pan-bay phenomenon,” he added.
“There’s a lot of nuanced things going on,” he said, such as the “weird phenomenon” of immature scallops having been unaffected by whatever killed the adult scallops, and the fact that scallop populations seeded by the Cooperative Extension showed no mortality — only the naturally spawned population succumbed.

“Personally, I don’t think we’ll see it happen next year,” he said, referring to another adult die-off. “If there’s a good enough set out there [of surviving bug scallops], there will be a cohort in the spring that are going to be adults for baymen to harvest.”

Further study is required, and the Cornell Cooperative Extension is seeking funding from multiple sources to pay for it, Mr. Tetrault said. “Everyone wants to find the smoking gun,” he added.

Eric Shultz, the president of the Southampton Town Board of Trustees, which regulates town waters, said he was glad to see “they started a pathology lab” at Stony Brook “and got to the bottom of this.”

He considers the parasite just one factor “in a lot of stress from the environment” and noted the same anomaly cited by Mr. Tetrault: Seeded scallops that the Town Trustees grow in Shinnecock Bay near Shinnecock Inlet, where there is constant flushing of the bay waters, flourished in 2019 and remain one source of the very pricey bay scallops that can be found in some local seafood shops. Local bay scallops were available and selling for more than $40 a pound at the Seafood Shop in Wainscott last week.

Before last year’s catastrophe, bay scallop harvests had been bouncing back from brown tide die-offs in the 1980s and 1990s, with baymen bringing in more than 108,000 pounds in 2017 and 2018 that had a dockside value of $1.6 million, according to the DEC. Then came the summer of 2019 and mortality estimates of more than 90 percent among the bay system’s naturally spawned adult scallop population.

“Although the exact cause of the die-off is unknown,” the DEC said in its announcement, “scientists theorize that the mortality event was due to physiological stress during bay scallop spawning, which was exacerbated by high summer water temperatures (mid-80s) and low dissolved oxygen. The detection of this parasite in bay scallops from Peconic Bay is also considered a contributing cause of the die-off last year.”

The parasites were found to have infected the kidneys of both juvenile and adult bay scallops in the Shelter Island sample, with extensive damage of the renal tubes noted in some, the DEC reported.

“Further research is needed to determine the life cycle, rate of infection, transmission, geographical distribution and environmental requirements of the parasite,” the DEC said.