Samples from Bowhead Whales Link Ocean Warming to Rising Algal Toxins in Arctic Waters

Rising toxins found in bowhead whales, harvested for subsistence purposes by Alaska Native communities, reveal ocean warming is causing higher concentrations of algal toxins in Arctic food webs, according to new research published today in the journal Nature .

The trend threatens food security for coastal communities that rely on marine life including clams, fish, and whales for food and other resources, researchers said. Communities in Alaska are now asking researchers to help them continue to monitor the emergence of algal toxins in the Arctic ecosystems that they depend on.

"These are new risks that were previously unknown," said Kathi Lefebvre, a research scientist at NOAA Fisheries' Northwest Fisheries Science Center in Seattle and lead author of the new study. "The people in remote communities in northern and western Alaska rely on marine resources for nutritional and cultural well being. Now we're finding that these resources are at risk."

"Native communities know intimately the ecosystems they rely on, and were among the first to recognize the effects of warming," said Raphaela Stimmelmayr, a wildlife veterinarian with the North Slope Borough in Barrow, Alaska, and a coauthor of the new research. She said the communities now need reliable tools such as field tests so they can test for the presence of algal toxins in traditional foods in real-time. These tests also help them make informed decisions on whether the marine mammals or other marine wildlife-such as clams, fish, and birds-are safe to eat.

"It is very difficult to walk away from resources that they need and have relied on since time immemorial," she said.

Lefebvre began studying harmful algal blooms as a graduate student in 1998. She documented domoic acid from the algae Pseudo-nitzschia causing seizures in California sea lions in central California. That was the first evidence that domoic acid-producing algal blooms could sicken and kill marine mammals. With the blooms growing more frequent, she has since followed an unmistakable trend of warming ocean waters and increasing algal blooms north to the Arctic.

Whales Collect Samples

Lefebvre leads the Wildlife Algal-toxin Research and Response Network for the U.S. West Coast . This alliance of agencies and institutions collects wildlife tissue samples from as far North as the Beaufort Sea in Alaska to Southern California. Members then send the samples to her Seattle lab to test for the presence of algal toxins. The lab's early work found that many species in Alaska had evidence of exposure , although not at levels high enough to be considered harmful to the animals sampled.

Over two decades, the lab regularly tested bowhead whales harvested during annual fall subsistence hunts in the Beaufort Sea off the North Slope of Alaska. The whales filter seawater for their food, consuming krill that contain algal toxins acquired from the food web. Lefebvre and her partners realized that fecal samples from the whales could reveal toxins in the marine environment the whales depend on.

"Nobody had a data set like this," she said. "Instead of going out every year and collecting samples across the marine environment, the whales did it for us. Their samples give us a snapshot of what is in the food web every year, as sampled by the whales."

After testing 205 bowhead whales over 19 years from 2004 to 2022, Lefebvre and her research colleagues decided they had enough data to look for changes over time. In particular, they wanted to track the concentrations of domoic acid and saxitoxin, another algal toxin produced by a marine algae called Alexandrium .

They found saxitoxin in at least half to 100% of the bowhead whales sampled each year over 19 years. That prevalence is even higher than that found for domoic acid (some years had zero prevalence). This is likely because saxitoxin-producing algae also form cysts that fall to the ocean floor during blooms. They accumulate until warmer bottom water conditions cause them to germinate and to seed a new bloom and more toxin production. This presents a second source for bloom initiation for this species. It is consistent with other studies showing that warmer ocean conditions increase the risk of Alexandrium blooms in the Arctic.

"Some of the biggest beds of Alexandrium cysts in the world lie in northern Alaskan Arctic oceans," Lefebvre said. Historically, bottom water temperatures have been too cold for cyst germination. However, over the last decade, bottom temperatures have periodically become warm enough for them to begin germinating.

"This is like a sleeping giant awakening," she said.

Winds, Ice Cover Affect Toxins

The scientists used ocean and climate data from a monitoring buoy in the Beaufort Sea to compare toxins in the bowhead whales to a measure of ocean temperature called heat flux.

They found that-based on the dominant currents in the Arctic-the whales feeding in waters with higher heat flux generally contained higher concentrations of the algal toxins. They also found that the winds that drive major currents in the Arctic could also help reduce or increase the heat flux into the Beaufort Sea. This would in turn reduce or increase the risk of harmful algal blooms.

"Warmer conditions are more favorable for harmful algal bloom growth and are correlated with higher toxin concentrations in the food web," Lefebvre said. "Atmospheric conditions influence the oceanography which influences the bloom dynamics. It's all connected."

They also compared the bowhead samples to changes in sea ice. Sea ice historically covered large sections of the Arctic, but has radically declined in recent decades. When there is less sea ice, sunlight warms the ocean more quickly and algae grows faster. Years with the largest reductions in sea ice cover in June led to warmer water in July. This boosted the odds of harmful algal blooms and rising toxin levels in the whales.

"Warmer ocean conditions and loss of sea ice are all linked to higher toxin levels in the food web," Lefebvre said. "The dots are all connected."

This extensive research was accomplished through decades of collaboration among researchers from tribal, state, and federal governments, academic institutions, and private organizations. Arctic science is best when there is teamwork amongst Native and western science. The research team included specialists in Arctic traditional ecological knowledge, oceanography, climatology, harmful algal blooms, food web ecology and experts in bowhead whale health and ecology. These researchers were able to fill in a piece of the Arctic harmful algal bloom risk puzzle. This study confirms the need for continued and increased monitoring of harmful algal bloom risks to food security and food safety of marine subsistence resources used by rural Alaskan communities.