When it comes to monitoring for red tide in Maine, one of Harpswell’s countless inlets and coves often provides the first alarm.
During a red tide event, concentrations of potentially lethal toxins begin to accumulate in shellfish that feed on phytoplankton, one-celled plants that thrive in the sunlit upper layer of the ocean. Filter feeders such as clams, mussels and oysters subsist on these tiny marine plants. As they ingest the plankton and concentrate the toxins in their bodies, they can become poisonous. People who eat them may become sick or even die.
It is the job of the Maine Department of Marine Resources to ensure the shellfish harvested in Maine is safe to eat. A crucial part of that responsibility involves monitoring the state’s waters for signs of dangerous red tide outbreaks. And the place where they are most likely to spot the first signs of potentially harmful phytoplankton is Lombos Hole in Harpswell.
A strategic approach
Bryant Lewis supervises the department’s red tide monitoring program along the southwestern half of the Maine coast. It would seem to be an overwhelming task. Maine, he observed, has one of the longest coastlines of any state in the country. It would be impossible to closely monitor every cove and bay in a state with thousands of miles of coastline.
The primary red tide threat in Maine is from a species of phytoplankton called Alexandrium fundyense, or Alexandrium for short. The neurotoxin it produces is the cause of paralytic shellfish poisoning. As its name suggests, victims can suffer paralysis, leading to respiratory failure and death.
Despite the name red tide, the water does not change color when an Alexandrium bloom occurs in Maine. You have to test to know it’s there.
“We have to be strategic in our approach,” Lewis said.
That means concentrating the search in places where toxicity is most likely to appear first and then expanding the search outward.
“The nice thing about Alexandrium is that it is fairly predictable in timing and the location where you find it,” Lewis said.
Alexandrium is primarily an offshore phenomenon. As a result, it tends to show up along points of land jutting out into the Gulf of Maine, as well as in the seaward sections of bays.
Red Tide is also a seasonal phenomenon. In the case of Alexandrium, toxicity usually shows up in the spring and subsides in the fall. The state does water sampling year-round, but only tests shellfish tissue for Alexandrium toxicity beginning in March and ending in October.
There are two other species of phytoplankton found in Maine waters that can make people sick. One is responsible for diarrhetic shellfish poisoning, the other for amnesic shellfish poisoning. As the names suggest, one is associated with diarrhea and the other with amnesia.
The state tests for all three, but to date only Alexandrium has posed a serious threat to human health in Maine, with two exceptions. In 2016 and again in 2017 there was a phytoplankton event when shellfish were found to contain high concentrations of the toxic substance that causes amnesic shellfish poisoning.
Sentinel site, sentinel species
The Department of Marine Resources has 18 primary monitoring stations around the state, chosen because decades of historical data say they are where toxicity is most likely to show up first. That history says that Lombos Hole, on the eastern shore of Harpswell Sound near the bridge linking Great and Orr’s islands, is the spot most likely to show the first signs of a problem.
“Lombos Hole is often the first one to tell us it’s coming,” Lewis said.
That was true again this year, when Alexandrium turned up in Lombos Hole on April 30. So Lombos Hole is a true sentinel site, reliably giving monitors their earliest warning of trouble ahead.
So far, this year has been typical. In May, the state closed almost the entire coast to the harvesting of mussels and European oysters, along with several other species, while allowing soft-shell clammers and quahoggers to keep digging.
Species of shellfish vary widely in how quickly they accumulate the Alexandrium toxin. There could be a number of reasons why, according to Lewis. Some species may be selective in what they eat and reject Alexandrium. Others may stop eating when they detect its presence.
As a result, harvesting of mussels and European oysters may be prohibited when soft-shell clams, quahogs and American oysters remain safe to eat.
In a way, this variation in toxin uptake simplifies the state’s task. Just as Lombos Hole is a sentinel site, mussels are the sentinel species used in the monitoring process. Their rapid accumulation of toxin makes them ideal for revealing the presence of the poison. (While mussels are the primary kind of shellfish used for biotoxin testing, the Department of Marine Resources does test other species, such as clams and oysters, to confirm they are safe to eat when toxin has been found in mussels.)
The department’s field workers usually collect wild mussels, which historically have been numerous along the coast, for testing. But in recent years, mussel populations have dwindled in some areas. In response, last year the department tested using cages that resemble lobster traps and contain bags of mussels gathered elsewhere. One of these cages is now in use at the Lombos Hole monitoring site.
The department checks its monitoring sites once a week. “If it’s a large plume, some twice a week,” Lewis said.
A leader in testing and technology
In the past, the state tested for shellfish toxicity by injecting shellfish tissue extract into mice. The rapid death of a mouse would indicate high toxicity levels. This method, called mouse bioassay, has been replaced by a method that is quicker, less expensive and more precise, while not harming mice.
In 2014, the Department of Marine Resources began using a high-tech method called high performance liquid chromatography. This technique was adopted for testing in partnership with Bigelow Analytic Services, an arm of the Bigelow Laboratory for Ocean Sciences in East Boothbay.
High performance liquid chromatography permits fast and accurate detection and measurement of toxins in mussel samples through recognition of the unique chemical color signatures of chemicals in a liquid.
At its lab in West Boothbay Harbor, the Department of Marine Resources prepares the shellfish samples for testing. Bigelow then performs the actual tests for the toxins that cause paralytic, amnesic and diarrhetic shellfish poisoning at its lab in East Boothbay.
The Department of Marine Resources does some in-house testing for the toxins that cause amnesic shellfish poisoning, but the department’s labs have not yet been approved by the U.S. Food and Drug Administration for regulatory purposes. That means the state cannot use its own test results as a basis for reopening areas that have been closed to harvesting. But it can use them to detect the presence of toxins and make closure decisions more quickly and efficiently.
Alexandrium first struck in Maine in a big way in 1972, when clam harvesting was shut down along the entire coast. The first intensive monitoring by the state began soon after.
“Maine has a long history of biotoxin testing,” Lewis said. “We’re leading the country in a lot of ways.”
While other places have begun using high performance liquid chromatography, Maine was among the first, Lewis said. And the development of in-house testing capacity for the amnesic shellfish poisoning toxin is an example of “the achievements we have made in recent years,” he said.
Maine can be proud of its history of making sure its seafood is safe to eat, according to Lewis.
“In the past 50 years, the only illness has been from people illegally harvesting from places that have been closed,” he said.
