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Little Known About Algal Toxins’ Effects on Subsistence in Arctic Waters

Clams from the Bering Strait Region were tested earlier this year and determined to have high levels of algal toxins. No one ate them and no illnesses were reported to the State related to these clams. But when the discovery was announced in November, the toxic clams highlighted how much scientists have yet to learn about algal toxins’ effects on subsistence food sources in the Bering and Chukchi Seas.

The U.S. Coast Guard Cutter Healy was out on a research cruise this summer, sampling several organisms like krill, worms and clams in the Bering and Chukchi Seas. Alaska Sea Grant’s Gay Sheffield says two different samples of clams from that voyage were found to have high levels of an algal toxin called saxitoxin.

“The two locations where it was above the seafood safety regulatory limit for the sale of clams were 70 miles north of Saint Lawrence Island and 50 miles north of Cape Lisburne.”

– Gay Sheffield

This is not the first time scientists have found saxitoxin present in several types of marine animals, as a study released in 2016 points out.

Graphic from Kathi Lefebvre’s 2016 report on algal toxins in Alaskan waters. (2019)

Kathi Lefebvre, a research biologist onboard the Healy at the time, explains that those two locations were not the only places where saxitoxin was present. The researchers found several types of organisms containing low to moderate levels of saxitoxin throughout the Bering Strait region this summer.

But what surprised Lefebvre was the high levels of saxitoxin found in the samples of clams, taken from deep sediments.

“As far as I know, I don’t believe this has been detected before at this kind of level, in shellfish from that region. That was what was surprising to me… these clams were deep, 30 meters or so in Arctic waters.”

– Kathi Lefebvre

So why would clams in the Chukchi Sea, at 30 meters in depth, contain high levels of saxitoxin? Scientists say it’s because the Alexandrium cysts that produce algal toxins are already pervasive in Arctic waters, and clams are most likely eating these toxic algae.

“We’ve seen these blooms in that area for two years straight, and we’ll be going up (to the Chukchi Sea) on a research cruise again, next summer.”

– Don Anderson

According to Don Anderson, a senior scientist with Woodshole Oceanographic Institute, there is evidence that dense Alexandrium cysts are a persistent feature in the Chukchi Sea. He says the cysts are causing annual harmful algal blooms [HABs], which are creating more saxitoxin. 

In fact, Anderson says, the number of cysts in the Chukchi is the highest they’ve seen compared to anywhere else in the world.

“It’s not unlike someone that has a lawn and has dandelions or crab grass that come back every year, that’s because there are seeds that are there and they just keep germinating every year and making new seeds. Then they’re there for the following year.”

– Don Anderson

With years of research showing saxitoxin is not new to the Bering Strait region, and that it is likely to be present in the future, Lefevbre and other scientists want to know at what point would algal toxins threaten the health of marine mammals.

“What we don’t know about the Bering Strait and Arctic areas are: are the toxins getting high enough in those regions to cause health impacts in marine mammals? We know that they cause health impacts in marine mammals in other places in the world. But what we’re doing now is looking at these toxins in the food webs in the Arctic, so that we can determine if the toxins are getting high enough to impact those animals.”

– Kathi Lefebvre

The same marine mammals that are used as a food source by many residents of the Bering Strait Region. Whaling captain George Noongwook of Savoonga says his community relies heavily on Bowhead whales and walrus for food.

“Most of the clams we get are from the walrus stomach. You can tell pretty much how healthy they (walrus) are just by the condition of the mammal.” 

– George Noongwook

Noongwook went on to say that it seems that the walrus are, on average, healthy based on what Savoonga subsistence users have seen. According to the U.S. Fish & Wildlife Service, their agency continues to partner with Savoonga, Gambell, and the Eskimo Walrus Commission to sample walrus during the spring harvest on St. Lawerence Island. The latest sample analysis says 52% of the tested walrus contained saxitoxin, but none were “reported to be symptomatic.”

Sampled clams taken from the USCG Healy’s research cruise this summer. Photo courtesy of NOAA Fisheries (2019)

Walrus eat clams, like the ones found with high levels of saxitoxin, and those toxins can be passed through the food chain all the way to humans who consume walrus for subsistence. When people eat contaminated seafood with high levels of algal toxins it can cause Paralytic Shellfish Poisoning (PSP).

State epidemiologist Louisa Castrodale with Department of Health and Social Services (DHSS) says no cases of PSP have been reported in the Bering Strait Region this year. A suspected case was reported on the Alaska Peninsula this summer.

But, Castrodale also says it is unknown what exact level of saxitoxin within marine mammals would cause PSP in humans if they ate it.

“The only sort of threshold we have is that level that’s set by FDA (Food and Drug Administration) for commercial shellfish. And so that 80 micro-grams per hundred grams of shellfish is that number. There’s no sort of number for like parts per million or billion in walrus tissue or in some other sort of substrate beyond that shellfish.”

– Louisa Castrodale

Sheffield and other regional residents believe there should be more testing of subsistence foods, and not just one safeguard in place when it comes to eating contaminated seafood.

“All those clams have been tested before they can be sold, so you have no concern when you go into a restaurant and order a clam chowder, you have no concern you’re going to get sick at all. For subsistence there is no system in place yet for required testing by these agencies to make sure everything is clean.”

– Gay Sheffield

There is no indication that a seafood safety guideline will be created by the Food and Drug Administration or other agencies for subsistence foods, like the FDA’s regulatory limit for shellfish.

For now, a network of scientists and agencies called WARRN-WEST will do more research on Harmful Algal Blooms and the toxins they produce. Their research could be used to create models to inform people ahead of time about high levels of saxitoxin in their area. Anderson and a team from Woodshole will conduct a research cruise in the Chukchi Sea next summer focused solely on these topics.

While that research is ongoing, Sheffield urges Bering Strait residents to remain vigilant, report any marine wildlife behaving unusually to Alaska Sea Grant at 434-1149 or Kawerak’s Subsistence Program at 443-4265, and if you feel sick after eating seafood please contact your local health provider immediately.

Image at top: Brownish-red algae covered rock is seen in the foreground of Cook Inlet. Photo from Alaska ShoreZone Program NOAA/NMFS/AKFSC; Courtesy of Mandy Lindeberg, NOAA/NMFS/AKFSC. (Flickr)

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