Scientists have discovered yet another sign of persistent warming in Arctic waters off Alaska.
For the first time, officials report, clams with dangerously high levels of an algal toxin that causes paralytic shellfish poisoning have been found in the Bering Strait region and in the Chukchi Sea — much farther north than sites where shellfish containing the toxin are usually found.
Clams collected at two sites by researchers aboard the Coast Guard icebreaker Healy had concentrations of saxitoxin at levels considered dangerous for human consumption. The clam samples were collected in August at a northern Bering Strait site about 70 miles north of Alaska’s St. Lawrence Island and at a Chukchi site about 50 miles north of Alaska’s Cape Lisburne.
Along with the saxitoxin-laden clams, researchers found thick dense concentrations of Alexandrium, the algae that produces the toxin, all the way to Chukchi Sea waters north of Utqiagvik, the northernmost U.S. community.
The results were announced by the Woods Hole Oceanographic Institution, which organized the sampling aboard the Healy, the University of Alaska Fairbanks’ Sea Grant program, the National Oceanic and Atmospheric Administration and other organizations.
The discoveries mark a turning point for scientists.
Previously, it was believed that the northern Bering Sea and Chukchi Sea waters were safe from such harmful levels of this algal toxin.
“We always tended to think it was too cold and the days were too short. And obviously, that’s not the case,” said Don Anderson, a Woods Hole algal expert who helped coordinate the 2018 and 2019 sampling program.
The results add to mounting evidence of a climate transformation that is occurring in the Bering and Chukchi seas. Those areas have been struck by extreme retreat of sea ice, including two consecutive winter meltdowns; sea-surface temperatures persistently well above normal; mass die-offs of seabirds and marine mammals; a northward shift of boreal species such as Pacific cod that are crowding out higher-fat Arctic species; and, thanks to extended periods of open waters, waves and storm surges that are reaching land in winter, previously a season of dependably frozen waters.
Paralytic shellfish poisoning can be deadly, and the blooms of Alexandrium algae that trigger it develop in relatively warm waters.
Previous NOAA research in the Puget Sound area showed that Alexandrium thrive there at temperatures ranging from about 8 degrees Celsius to about 24 degrees Celsius, depending on salinity. In the past summer, waters in the Bering Strait region and points north reached that temperature range.
The discoveries of toxin-laden clams and dense Alexandrium blooms as far north as the Chukchi is “clearly related to temperature,” said Kathi Lefebvre, a research biologist with NOAA’s Northwest Fisheries Science Center who has helped lead the Arctic Alaska monitoring program.
Shellfish harvesters and growers in more southern areas like southeast Alaska and Puget Sound regularly monitor algal blooms and their potentially harmful effects. Dense blooms and high levels of toxins have, in the past, closed shellfish harvests in regions of southern Alaska, in the Pacific Northwest and in places such as the Gulf of Maine.
So far, there have been no reports of anyone in the Bering Strait of Chukchi Sea region affected by paralytic shellfish poisoning. The sites where the toxin-laded clams were collected were in waters 31 to 55 meters deep and far away from any place where people would be harvesting seafood, Lefebvre said.
But those clams were in areas where marine mammals forage — and marine mammals are the focus of Lefebvre ‘s research.
There is growing evidence that even in Arctic waters off Alaska, marine animals are being exposed to algal toxins.
A 2016 study led by Lefebvre described how tests conducted over a decade found traces of algal toxins in all of the 13 examined marine mammal species, from large whales to small sea otters and in a geographic area that stretched from the Gulf of Alaska waters off the tip of southeastern Alaska to the Beaufort Sea off Arctic Alaska’s northern coast. Samples of dead and live seabirds from species affected by recent years’ die-offs found traces of saxitoxin, scientists reported last year. And four walruses that died in the Bering Strait region in 2017 were found to have algal toxins in their bodies.
But just what levels are dangerous to mammals and birds has yet to be determined, Lefebvre said. Also unknown is whether algal toxins were responsible in any way for the animal deaths, including the recent die-offs of ice-dependent seals that prompted NOAA in September to declare an “unusual mortality event” and mobilize a broad-ranging investigation.
“There is no answer to that because there are multiple things at play here,” Lefebvre said. Other possible causes include lack of sea ice animals need for resting, lack of food or lack of the right kind of food, she said. “It may be a mixture of multiple factors,” she said.
The potential for Alexandrium blooms as far north as the Chukchi has been known for a few years. The existence of Alexandrium cysts growing on the seafloor there was confirmed by Japanese scientists who surveyed the eastern Bering Sea and Chukchi Sea from 2009 to 2012.
But now it appears that a threshold has been crossed — those cysts are blooming, and the resulting algal toxins may be a fact of life in Alaska’s Arctic waters.
“It is unprecedented. I don’t see how we can go back,” Lefebvre said.
In Gulf of Alaska waters farther south, warming waters have forced another new health-related change.
A type of bacteria that proliferates in warm conditions, Vibrio parahaemolyticus, is now a recognized infection hazard. Infections can cause acute gastroenteritis, with symptoms that include diarrhea, nausea and vomiting.
The world’s northernmost known case of Vibrio parahaemolyticus infection occurred in Alaska in 2004, when several cruise passengers were sickened after eating oysters from Alaska’s Prince William Sound.
In the aftermath of that outbreak, the state Department of Environmental Conservation developed a formal protocol instructing shellfish harvesters how to avoid Vibrio-related illnesses. There have been cases of Vibrio infections in Alaska every year from 2005 to 2018, but major outbreaks have been avoided through the control protocol, according to a recent bulletin from state’s epidemiology office. Cases spiked in 2018, however, according to the bulletin.
All of the Alaska cases are believed to be related to oyster consumption, said Louisa Castrodale, acting manager of the Alaska Division of Public Health and Epidemiology’s infectious disease program.
Vibrio parahaemolyticus counts increase as water temperatures rise, particularly over 60 degrees Fahrenheit, according to the bulletin.