by Kim Krisberg
Every week, the Rhode Island State Health Laboratory tests water from Narragansett Bay, monitoring the estuary for harmful toxin producing plankton that can contaminate the seafood that makes it to market. The testing protects both consumers and the fishermen who depend on a healthy bay for their livelihoods.
Last October, that routine testing revealed large numbers of the algae Pseudo-nitzschia — numbers much higher than what’s considered normal. Pseudo-nitzschia can produce a neurotoxin known as domoic acid. In people, domoic acid can lead to amnesic shellfish poisoning, which can result in permanent short-term memory loss and even death. So with the sudden algal bloom detected, laboratory staff quickly began toxicity testing. Tests came back positive.
The results meant the public health laboratory had just detected Rhode Island’s first Pseudo-nitzschia bloom and triggered a statewide contingency plan designed to keep contaminated shellfish from reaching people’s plates.
“Our goal is to protect public health, but this could also affect the shellfishing economy and the harvesters here — the whole reputation of Rhode Island shellfish could go down the drain if people did get sick,” said Henry Leibovitz, PhD, chief environmental laboratory scientist at the Rhode Island Department of Health State Health Laboratories.
Contingency plan activated, laboratory staff began testing shellfish meat collected from areas with high algae counts. The meat tested positive for domoic acid levels beyond safe thresholds set by the US Food and Drug Administration. In response, on October 7, Rhode Island’s Department of Environmental Management (DEM) officially closed down shellfish collection in parts of the bay. Leibovitz said it was the first time this particular type of algal bloom brought shellfish harvesting to a halt in the area.
As harvesting on the bay stopped, laboratory staff ramped up their testing of water and meat samples collected by the DEM as well as of quarantined shellfish already on the market.
“We wanted to prevent contaminated shellfish from getting to people and reopen the bay as soon as it was safe,” Leibovitz said.
Thankfully, none of the quarantined shellfish tested positive for contamination and within a few weeks, algae counts began dropping. A few weeks after the bloom began, Leibovitz said the number and density of plankton declined to a point where the shellfish had a chance to cleanse themselves of the toxin. Laboratory staff began seeing results well below safety thresholds so that Rhode Island shellfish were safe for consumption. By the beginning of November, DEM reopened the bay to shellfish harvesting.
Then in February, the laboratory detected another Pseudo-nitzschia bloom and high toxin levels — this time, in a part of the bay closest to the ocean. (On a side note, Leibovitz said some experts speculate that the initial bloom never really died out entirely off shore, and the bloom returned to the mouth of bay where it meets the ocean.) Based on the results, DEM shut down shellfish harvesting again on March 1, eventually reopening on March 24.
Throughout the two closures, no cases of human illness related to contaminated shellfish were reported.
During the blooms, laboratory scientists conducted hundreds of complicated tests in the span of a single month — “everyone had to stay late and get it done because we needed the answers right away,” Leibovitz said. He noted that even though the laboratory is prepared for such a surge, it’s still “very challenging” to keep up for weeks at a time.
That’s because within the laboratory’s water microbiology unit, none of the four scientists do shellfish testing on a full-time basis. They’re also responsible for testing drinking water, beach water, dairy samples, river water and animals for rabies. But when the algal bloom appeared, the entire water microbiology laboratory turned its attention to keeping toxic shellfish off people’s plates and re-opening the bay as quickly and safely as possible. At one point, scientists from a different division within the state laboratory were called over to help.
“It’s very time-consuming and our other responsibilities don’t stop,” Leibovitz noted. “We’ve always had a contingency plan in place, but the laboratory isn’t staffed to do this (level of testing) on a routine basis and last fall, it became routine.”
So, what caused the algal bloom? Leibovitz said, “no one really knows yet.” But one theory is that successful efforts to keep stormwater runoff out of Narragansett Bay has reduced nutrients in the bay to the point that Pseudo-nitzschia may not have the competition from other algal species that flourished for years in the nutrient-rich environment. The cleaner waters of the bay may now be more supportive of Pseudo-nitzschia growth as are the waters outside of the bay, where they typically thrive.
“The worry is that this could be the new normal,” Leibovitz said. “But the group that works in the water microbiology laboratory are really dedicated to ensuring Rhode Island shellfish in the market are good and safe to eat…when something like this happens, they step up.”
According to the Centers for Disease Control and Prevention, it’s unknown how many people in the US are sickened due to harmful algae blooms, as such occurrences aren’t tracked nationally. However, state and local public health agencies can now report such illnesses to the One Health Harmful Algae Bloom System, which launched last year. CDC did report that economic costs associated with such blooms have gone up in recent decades, costing the fishing and tourism industries millions of dollars each year.