LAMOINE — Last week, the Department of Marine Resources closed a stretch of the Downeast coast to the harvesting of clams, mussels, oysters and carnivorous snails.
The closure was a precaution because of concerns about the presence of high levels of the marine organisms that produce domoic acid, the biotoxin that can cause ASP, amnesic shellfish poisoning.
On Tuesday, DMR announced that, effective at 12:30 p.m. Wednesday, it was extending the closure to encompass the entire area stretching from Grindstone Point in Winter Harbor eastward to Point of Maine in Machiasport.
On Sept. 7, the department had closed the area between the southern tip of Petit Manan in Steuben and the southern tip of Pond Point on Great Wass Island.
DMR’s Public Health Bureau tests coastal shellfish areas for biotoxins weekly, from March through October, or later when testing indicates the continued presence of biotoxins.
Testing includes sampling of water to determine the species and concentration of marine algae known as phytoplankton, which produce biotoxins.
For most types of phytoplankton, when routine water sampling detects cell concentrations (in terms of numbers of cells per liter of water) that are known to produce toxins, sampling of shellfish begins. When shellfish samples have toxins in concentrations specified by the National Shellfish Sanitation Program, areas are closed to shellfish harvesting.
While toxin levels in shellfish sampled in the affected area fall below the NSSP threshold for closures, Maine DMR has determined that Pseudo-nitzschia, the marine algae that produces domoic acid, causes shellfish to become toxic more quickly than other species of phytoplankton.
The use of precautionary closures for ASP is designed to prevent the need for recalls from the marketplace of shellfish harvested between initial and follow-up sampling.