Potential Toxic Phytoplankton Bloom Shuts Down Nantucket Sound Shellfishing

By: Tim Wood

Topics: Commercial fishing and shellfishing , Shellfishing

Shellfishing along the Cape's south coast, including Nantucket Sound, was banned by the state Monday due to a potentially toxic phytoplankton bloom. TIM WOOD PHOTO

A toxic plankton bloom prompted state officials to close all of Nantucket Sound to shellfishing Monday.

The closure includes all of the waters, flats, bays and embayments along the south coast of Cape Cod. That includes Stage Harbor, Mill Pond, Mitchell River, Forest Beach, Cockle Cove Beach and Ridgevale Beach.

In Chatham, waters to the east of Morris Island, including the Southway, Chatham Harbor and the entire east coast, remain open to shellfishing.

The state division of marine fisheries banned shellfish harvesting in Buzzards Bay on Oct. 7 because of a “substantial bloom” of a potentially toxic form of phytoplankton called pseudo-Nitzschia, according to a press release from the agency.

Chatham Shellfish Constable Renee Gagne said state officials were in town Tuesday taking water and oyster meat samples. The phytoplankton algae bloom can cause amnesic shellfish poisoning (ASP), a potential serious condition.

“It can cause gastro issues, but can also affect short term memory and cause permanent brain damage,” she said. The responsible phytoplankton is “similar to red tide,” she added, “but is a different type of algae that causes a different type of human illness.”

She stressed that no cases of illness attributed to the bloom have been reported locally. No recall was issued on previously harvest shellfish, leading her to believe that the closure is precautionary.

Chatham issues hundreds of commercial shellfish licenses and dozens of shellfishermen dig quahogs, steamers and mussels full time. Gagne said many of the areas impacted by the closure, including Oyster Pond, were already under seasonal closures, and with the Southway and east-facing areas still open, local shellfishermen have an alternative.

“Really one of the more productve areas is still open, which is the Southway,” she said.

DMF stated that pseudo-Nitzschia can produce domoic acid, a biotoxin that accumulates in the guts of filter-feeding shellfish. Shellfish with high concentrations of the acid cause ASP, the symptoms of which include vomiting, cramps, diarrhea and incapacitating headaches, followed by confusion, disorientation, permanent loss of short-term memory and in severe cases seizures and coma.

The state has given no indication how long the closure will last, Gagne said. The press release stated that areas will reopen once the bloom has dissipated and testing confirms the absence of domoic acid.

The closure does not include harvest of whelks, bay scallops or sea scallops for sale of the abductor muscle, which does not accumulate the toxin. Gagne said if the closures persists past the Nov. 1 bay scallop season opening, her department will put out information clarifying that only the abductor muscle can be eaten.