The state Division of Marine Fisheries (DMF) has announced that due to the results of samples taken last week, the Oct. 11 shellfish closure will continue in growing areas south of Cape Cod through at least Friday, Oct. 28. Only bay scallops are exempted. The closure was prompted by an expanding phytoplankton bloom of a potentially toxic species of the phytoplankton Pseudo-nitzschia, a diatom that has been shown to cause a neurological disorder.
“Anybody that’s been involved in this kind of work for any amount of time is saying this is ‘unprecedented’ in the number of cells per liter and the range that it covers,” Michael Hickey, shellfish program manager for the DMF, told The Times on Wednesday. “This has shut down shellfishing from southern Canada all the way down the Maine coast to the outer coast of Rhode Island, into Narragansett Bay. The readings in Maine have been much higher than we’ve found in this area. They’ve had to institute shellfish recalls, which we’re trying to avoid.”
Mr. Hickey said there is a great deal of conjecture about the cause of the bloom, but there are no answers as yet. “I don’t think anybody really knows; that’s the problem here, we don’t know what triggered this,” he said. “Right now it’s a good-news, bad-news situation. The bloom is starting to subside, but that’s when the phytoplankton gets stressed, and that’s when they produce the most toxin. So toxin levels are going up.”
The phytoplankton Pseudo-nitzschia, when concentrated in the gut of shellfish, can cause amnesic shellfish poisoning (ASP). ASP symptoms include vomiting, nausea, diarrhea, and abdominal cramps within 24 hours of ingestion. In more severe cases, neurological symptoms develop within 48 hours, and include headache, dizziness, confusion, disorientation, loss of short-term memory, motor weakness, seizures, profuse respiratory secretions, cardiac arrhythmias, coma, and possible death. Short-term memory loss can be permanent.
A second round of shellfish samples was also analyzed at the DMF Gloucester Shellfish Laboratory for concentrations of domoic acid (DA). The presence of DA was confirmed in quahogs collected from Buzzards Bay, but all other samples from that region tested negative for DA. “However, the continued presence of high Pseudo-nitzschia concentrations throughout Nantucket Sound and Vineyard Sound harvest areas warrants the continuation of the closure until additional analysis can be conducted,” a DMF release states. “It is important to note that this closure is precautionary; to date there have been no reports of ASP associated with the consumption of Massachusetts shellfish.”
Bay scallops are exempted from the closure because the toxin is concentrated in the gut, not in muscle tissue. Only the adductor muscles of scallops are eaten.
Local oyster farmer Jack Blake, owner of Sweet Water Farms, located in Katama Bay, said that so far, the closure is not posing a major problem. “It’s never a good time for a closure,” he told The Times. “But there’s many parts to running a farm; harvesting is only one part of it. I’m staying busy every day, there’s plenty of gear work to be done. This algae doesn’t harm the oysters. They’re getting fat right now.”
Mr. Blake said once the closure is lifted, it would probably be another week before harvesting, so the oysters can clean the bacteria out of their system.