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Peconic Bay scallops die-off tied to newly detected parasite

Peconic Bay scallops have seen mortality rates of

Peconic Bay scallops have seen mortality rates of from 90% to 100% in many eastern Long Island waterways this winter. Credit: Randee Daddona

The catastrophic die-off of Peconic Bay scallops in eastern Long Island waters may be tied to a previously undetected parasite that can infect the kidneys of adult and juvenile scallops, state regulators reported Friday.

The specific parasitic organism, known as coccidian parasite, was discovered in kidney tissue of all 32 scallops collected and sampled from Shelter Island’s Hay Beach last November, the state Department of Environmental Conservation said. Some scallops had “extensive damage” to renal tubes, enough to kill the most heavily infected, the DEC said.

The agency, working with Stony Brook University’s Marine Animal Disease Laboratory, said the parasite “represents a significant threat” to the scallops, but cautioned that “further research is needed” to study how widely the parasite may have been dispersed, its life cycle and rate of infection before it can be said with certainty that it was the direct cause of the die-off.

“This is a new factor that scientists think may have a prevalent effect,” a DEC spokeswoman said.

Biologists last year theorized a combination of factors may have spurred the catastrophic collapse of Peconic Bay scallops, which saw mortality rates of from 90% to 100% in many eastern waterways.

They said unusually warm waters and resulting low oxygen levels may have hit at the height off the scallops’ summer spawning season in July, putting heightened stress on the shellfish. There were also reports that large schools of cow-nosed rays spotted in eastern waters may have been feasting on scallops in numbers not previously seen.

Regulators on Friday were quick to point out that the coccidian parasite is not a public health concern and poses no danger to humans. But its potential impact to the bay-scallop fishery, if proved, was widespread. In the prior two years, baymen landed some 108,000 pounds of bay scallops during the early November to March 31 season, with an estimated value of some $1.6 million. This winter, many licensed scallopers put away their gear after just a week of fishing.

For many fishermen in eastern bays, scallops are an important component of their winter income.

Impacts were reported at local restaurants and wineries, fish shops and even roadside scallop stands that dot the East End, primarily on the North Fork, when scallop season opens.  

DEC commissioner Basil Seggos, in a statement, said the agency and Stony Brook scientists would continue to investigate “environmental factors that promote disease development of the parasite and monitor its geographical extent in bay scallops in Peconic Bay in order to protect and restore this ecologically and economically important resource.”

Despite the unexpected parasite finding, the DEC is still classifying the cause of the die-off as "unknown," though it now believes the parasite is “one of the causative factors.”

The coccidian parasite is one of a strain known as apicomplexan, which are found “in virtually all types of animals,” a DEC spokeswoman said. They can complete their life cycle in a single host, but some require multiple species, or hosts, to complete their life cycle. It's unclear whether the parasite found in Peconic Bay scallops requires one or more host species, DEC said.

It is also unclear how it turned up in the bay scallops to begin with. The DEC, Cornell Cooperative Extension and Stony Brook scientists will continue research to determine the origin of the parasite and whether its presence was triggered by environmental factors such as warmer bay waters, the DEC said.

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