Narragansett Bay Recovers from Algal Bloom, Shellfish Safe
An unprecedented algal bloom that spanned from Long Island to Maine triggered a shellfishing ban in Narragansett Bay for most of October. After it ended and shellfish beds reopened, fishermen, shellfish farmers, and environmental managers convened at a public meeting in December to try to understand what caused the bloom and what to do about future events.
Monitors found elevated counts of a type of plankton that was responsible for the bloom outside of Newport Harbor at the end of September, said Angelo Liberti, chief of water resources at the Rhode Island Department of Environmental Management (DEM), at the meeting held to share information that DEM and the state health department collected during the bloom, and to discuss future monitoring and testing efforts.
Liberti was referring to Pseudo-nitzschia, a genus of plankton that can produce domoic acid, a neurotoxin that, if ingested in dangerous amounts, can cause illnesses ranging from gastrointestinal problems and lethargy to short-term memory loss and seizures.
Although this type of plankton is always present in the bay and elsewhere, it is unclear what prompted the bloom. After a rapid increase in cell counts was detected in early October, DEM issued shellfish closures for all of Narragansett Bay (but not in the coastal salt ponds), the Sakonnet River, and Mount Hope Bay. These closures required dealers to hold all shellfish until tests could be made to determine whether the toxins were present at levels of concern.
After several weeks of test results showing the shellfish were not toxic and declining cell counts in bay water samples, shellfishing areas were reopened only to be closed soon after in the lower Sakonnet River due to elevated cell counts and positive tests for domoic acid in plankton and shellfish in several locations. The second closure, which included whelk and moon snails, was issued even though levels of domoic acid found in shellfish were only half of the federal standard. Liberti said this was done to ensure consumer safety while more complete testing could be done. Then, as quickly as these cell counts had risen in the lower bay, they declined, according to DEM.
Although Fort Wetherill and Sakonnet Harbor tested positive for domoic acid in shellfish, the levels were far below standards considered unsafe for consumption. Closures were more precautionary in light of the rapid spread of the bloom in Maine that led to a recall of five tons of shellfish.
“We are not focused on all harmful algae that could carry toxins, we’re really focusing [on effects] that vector through shellfish to people,” he said, noting that state agencies strive to protect consumer health without overreacting and hurting harvesters.
While no illnesses were reported in Rhode Island, sales dipped for some local harvesters.
“When you can’t provide your product due to algal blooms, it sends a signal of alarm,” Bill Silkes, president of American Mussel Harvesters, said recently. He explained that media coverage of events like algal blooms can confuse consumers and hurt business. “We’ve got our oyster farm here in the bay that was subject to the closure, and I would say, at this point, our business for those brand of oysters is roughly a quarter of what it was prior to the closure … it can take a long time [for buyers] to get to a comfort level that our product is safe.”
Although closures can have a negative economic impact, Silkes points out that they’re a “sign that the system is working to keep seafood safe.” This sentiment was reiterated by Bob Rheault, executive director of the East Coast Shellfish Growers Association.
“The closures are prudent and proactive based on what we did and didn’t know,” said Rheault, noting that Rhode Island has never had a case of illness related to shellfish containing toxins in over 30 years. “In hindsight, it wasn’t necessary based on the levels [of domoic acid] found in shellfish meat. But it’s prudent to close it down until we get a handle on what’s going on.”
HAB Event Exposes Challenges
Testing plankton and shellfish samples proved to be a challenge for both DEM and the Department of Health. Sometimes weather prevented vessels from operating, and other times the necessary screening kits that had to be shipped from Canada occasionally were lost or held up in customs, said Liberti in an interview with the Narragansett Times.
Other challenges included collecting shellfish at certain depths and shipping the samples to a Maine laboratory – the closest of only two federally qualified labs in the country – which proved to be time-consuming.
Liberti explained improved testing capabilities and increased monitoring efforts are needed both locally and regionally to respond to emergency situations such as this. And even though the state has been monitoring algae species that have the potential to produce biotoxins since the 1970s, monitoring efforts need to be stepped up year-round, especially during peak bloom seasons during the summer and fall, said David Borkman, a DEM biologist specializing in phytoplankton.
“We’re trying to match how often to sample with bloom period when these particular organisms might be around. They’re only around in the summer, so there’s no sense in looking for them in the winter. And how often you looking should match the duration of the bloom.” he said, adding that abundance alone isn’t an indicator of biotoxin levels–tests should screen toxin production as well.
Discussions between DEM and the health department, along with agencies from other states, are underway to figure out how to best share resources and where to build capacity for monitoring and testing, as well as determine goals for future research.
Rhode Island Sea Grant has recently released a Research Request for Proposals to explore and better understand issues related to harmful algal blooms in Rhode Island waters.
“It’s part of Sea Grant’s mission to be responsive to such events,” said Alan Desbonnet, assistant director of Rhode Island Sea Grant. “A primary concern is identifying early warning signs of harmful algal blooms. We need to be looking more closely at how blooms in coastal waters, specifically Rhode Island Sound, enter the bay.”
Meredith Haas | Rhode Island Sea Grant Communications