The Massachusetts Division of Marine Fisheries has closed all shellfishing in waters south of Cape Cod until further notice, including Marion and Mattapoisett, due to a potentially toxic algae bloom. Waters from the Rhode Island border to Nantucket Sound are included in the ban.

The DMF announced that a phytoplankton called Pseudo-Nitzschia can contain the biotoxin domoic acid that concentrates in filter-feeding shellfish. The algae were found in very high concentrations in samples collected on Oct. 6 throughout Buzzards Bay. Mount Hope Bay has not been tested yet, but due to toxin-producing algae in nearby Narragansett Bay, the DMF issued the precautionary closure.

Consuming infected shellfish could result in amnesic shellfish poisoning, with symptoms that can include vomiting, cramps, diarrhea and incapacitating headaches followed by confusion, disorientation, permanent loss of short-term memory, and in severe cases, seizures and coma.

As a result of the closure, digging, harvesting, collecting and/or attempting to dig, harvest or collect shellfish, and the possession of shellfish, is prohibited in Mattapoisett, Marion, Bourne, Dartmouth, Fairhaven, Falmouth, Gosnold, New Bedford, Swansea and Westport.

The DMF is testing the waters of Vineyard Sound, Nantucket Sound and Cape Cod Bay for the presence of the phytoplankton. Additional testing of phytoplankton and shellfish for the biotoxin will be carried out within areas of the coast where significant algae blooms are detected.

Based on the results of further testing, DMF will reopen areas once the bloom has dissipated and shellfish are known to be free of toxic levels of domoic acid. The closure will not affect the harvest of whelks, bay scallops or sea scallops for purposes of extracting and selling or consuming.