Researchers find algal toxins in clams in Chukchi Sea
Researchers aboard the U.S. Coast Guard icebreaker Healy reported news from their August 2019 cruise that they found clams at two locations, one 70 miles north of St. Lawrence Island, another 50 miles north of Cape Lisburne, having high saxitoxin concentrations above seafood safety regulatory limits, which rendered them unsafe to eat.
Saxitoxin is a biological toxin that is produced by an algae called Alexandrium catenella. The researchers detected high concentrations of the algae during their August cruise this year as well as in 2018.
A bulletin bearing the logos of Alaska Sea Grant, the Woods Hole Oceanographic Institution, Alaska Ocean Observing System, NOAA, Alaska HAB network and the North Slope Borough, warns that the Alexandrium algae concentrations “were high enough in the seawater to potentially make shellfish unsafe to eat,” and that “clams at two locations had high saxitoxin levels and were unsafe to eat.” It also notes that most clams found in other locations weresafe to eat.
Saxitoxin, if ingested, causes Paralytic Shellfish Poisoning, PSP for short, and manifests in breathing difficulties, paralysis and can lead to death in humans and marine mammals.
Although the bulletin says there have been no PSP symptoms reported in the Bering Strait or Chukchi Sea region, the bulletin’s authors stress that “people should remain vigilant and immediately alert their healthcare providers if they feel sick after eating seafood in the Bering Strait/Chukchi Sea region.”
Saxitoxins are a well-known health hazard in Southeast Alaska and the eastern Aleutians. Commercially caught clams and crabs are tested for saxitoxins and the US Food and Drug administration has established a limit of 80 micrograms (a millionth of a gram) per 100 grams of shellfish to be safe. While commercially harvested seafood is tested, there is no field test available to test shellfish gathered for subsistence.
Clams and other shellfish can concentrate the biotoxin in their tissues as they eat tiny algae by filtering the ocean water.
Saxitoxins cannot be cooked out of the clams, nor can it be frozen out. It is still unknown how many nanograms per grams of saxitoxin consumption is harmful to marine wildlife, such as walruses, eating clams and mussels off the oceanfloor.
Kathi Lefebvre, research biologist with NOAA’s Northwest Fisheries Science Center, has done research over the past ten years in regards to harmful algal blooms and found saxitoxin and another algae-produced biotoxin called domoic acid in feces and stomach contents of walruses, whales and ice seals. In a phone interview with The Nome Nugget she said that those biotoxins have been documented in pretty much every arctic marine mammal species, “but there was no evidence of health impacts,” she said. The recent research cruises sampled clams, worms, krill and copepods and results showed that low to moderate levels of saxitoxins were present. “We’ve been concerned about harmful algal blooms in the subarctic and the Arctic,” Lefebvre said. However, this is the first time that the researchers have seen and documented clams with saxitoxin levels above the regulatory limit for safe consumption this far north, she said. They did not sample red king crabs or other crabs for saxitoxin.
Reached via email, Donald Anderson, Senior Scientist at the Biology Department and Director at the Cooperative Institute for the North Atlantic Region (CINAR) at the Woods Hole Oceanographic Institution responded to the Nugget’s questions. He wrote that the team of scientist aboard the Healy were able to document the spatial distribution and abundance of Alexandrium catenella cells in the water column and cysts in the sediments. “The cyst distribution confirmed our observations from 2018 - namely that they are very abundant in the Ledyard Bay area of the Chukchi Sea.” He also wrote that this time they were able to define a small, but very dense cyst “seedbed” near Utqiaġvik. “The motile cell distribution (these are the cells that swim in the water and are the main source of toxicity in the planktonic food web) was that of several large patches or blooms - one just north of the Bering Strait, a smaller and less dense one offshore of Ledyard Bay, and a third near Utqiaġvik,” he wrote. “Last year, we only saw a large bloom in Ledyard Bay. These new observations are interesting as they suggest that there may be several mechanisms to introduce toxic cells into the North Slope waters - transport from the Bering Sea in the south and local cyst germination.” The algal blooms are directly linked to the warming of Arctic waters.
He explained that half of the Alexandrium cysts in a bed take about one to two months to germinate at 32°F to 35.6°F. However, if sea temperatures rise, and if the temperatures are between 42.8°F and 50°F, that process can take only seven to ten days. “Those are the bottom temperatures we have seen in August at the location of the big seedbed in Ledyard Bay,” Anderson wrote. “That also means that the germination can be highly synchronized - so that a lot of cells are released to the water column at nearly the same time. When it takes months to germinate, the inoculum is much more dispersed in time,” he said. Climate Specialist Rick Thoman with UAF’s ACCAP confirmed that the ocean surface temperatures in August were in the mid 40s°F in the area where the clams were found north of St. Lawrence Island and that the ocean surface temperature was in the low 50s°F at Ledyard Bay.
Asked if the algal blooms are visible to the naked eye, Don Anderson said, no, they are not, even though the cell concentrations are high enough to produce dangerous levels of toxin. “It would take about 100 times more cells to discolor the water, and yet clams feeding on the concentrations we documented would get very toxic,” Anderson wrote.
When asked if he noticed any other signs of ecosystem distress such as sick birds or marine mammals around the areas of algal blooms, Anderson responded that there were a lot of dead or dying birds observed during the cruise, but many of these were south of the recorded algal blooms. “Since one of those blooms looks to have been transported through the Strait, the birds might have picked up some toxin as the bloom moved north. In other words, the birds might have remained in the area, while the bloom transited north,” Anderson responded.
Anderson added, “We are preparing a scientific paper on all of this data, as it is both surprising and important.
“I have been studying Alexandrium catenella in the Gulf of Maine region for more than 30 years, and that is an area with recurrent annual toxic blooms, so I have a solid perspective on the implications of our findings. That being said, the vectors for the toxin are different in the Arctic, as clams are not a huge resource.” He stressed that scientists have yet to find out how the toxin is transferred through the food web to seabirds, walruses and whales.
Kathi Lefebvre said that she teamed up with Anderson to develop a research plan to continue to document the locations of the algal blooms and getting samples from the food web in order to model the impacts of algal blooms on marine mammals and fish. Researchers don’t expect the toxin to accumulate in muscle or blubber, but they are not sure about accumulation in the kidney or liver. In addition to stomach contents and feces, she also now requests samples of internal organs, muscle tissue and blubber from her research partners and her network of community partners and subsistence hunters who supply samples from their harvests.
Anderson said the research cruise aboard the US Coast Guard Cutter Healy was conducted for the Distributed Biological Observatory program of NOAA and was funded by their Arctic Research Program. The Harmful Algal Bloom work was added to the regular schedule using the arctic research program support in both 2018 and 2019.
They also received funds from Polar Programs at the National Science Foundation.
Editor's note: This version was corrected that the regulatory limit of saxitoxin is 80 micrograms, which is one millionth of a gram, instead of 80 nanogram (one billionth of a gram), as was stated in an earlier version of the story.