Algae toxins are creeping north, scientists say, and marine mammals could potentially pay the price.
The National Oceanic and Atmospheric Administration released a study Feb. 11 that used samples from over 900 different marine mammals between 2004-2013 to test for toxic presence. The samples came from all over Alaska, from the Beaufort Sea to Ketchikan. Domoic acid and saxitoxin — two neurotoxins found in algae blooms — were found in a majority of the tested species.
NOAA doesn’t attribute any deaths directly to the algal toxins, but points out more than 40 percent of marine mammal unusual mortality events come from toxic algae. Kathi Lefebvre, a NOAA scientist who spearheaded the study, said that number is fairly conservative. Domoic acid and saxitoxin move quickly through the body and resulting deaths are difficult to attribute.
“I feel very confident that yes, there are likely deaths of marine mammals by toxins we cannot identify.” said Lefebvre.
The report verifies that algae toxins are spreading northward.
Reports have tied algal toxins to California sea lions since 1989 — more than 200 died or had seizures from algae toxins last year — but until now Alaska has had no documented domoic toxicosis and rare saxitoxin poisoning in its marine mammals. Last year, NOAA documented a sea lion seizing from algal toxins in Long Beach, Wash., the first time any such case had been recorded north of California.
Lefebvre clarified that the study finds no causal link between toxic presence and marine mammal deaths. The future, she said, is the concern.
“The risk is there,” Lefebvre said. “If we get increasing blooms, the risk will increase. That’s the concern. We know that warming waters and the loss of sea ice is more favorable for growth of algae.”
Part of the concern is food security; marine mammal die offs could affect subsistence communities who depend on them.
The study found the toxin levels far below regulatory limits for human consumption. Animals die long before muscle and blubber absorb enough toxins to affect humans.
Some communities do harvest shellfish from mammal stomachs, however, which could cause problems. The Alaska Department of Health has made no changes in guidance to seafood safety.
The study surveyed 13 species including humpback whales, bowhead whales, beluga whales, harbor porpoises, northern fur seals, Steller sea lions, harbor seals, ringed seals, bearded seals, spotted seals, ribbon seals, Pacific walruses, and northern sea otters.
“Domoic acid was detected in all 13 species examined and had the greatest prevalence in bowhead whales (68%) and harbor seals (67%),” reads the report. “Saxitoxin was detected in 10 of the 13 species, with the highest prevalence in humpback whales (50%) and bowhead whales (32%).”
Domoic acid, first documented in Alaska with Kachemak Bay razor clams in 1992, causes amnesic shellfish poisoning in humans. Saxitoxin causes paralytic shellfish poisoning. The two toxins have been documented in Alaska shellfish for decades, and the human effects of shellfish poisoning with them.
Algal blooms and their accompanying toxins usually feel at home in tropical or temperate waters. Alaska’s sub-Arctic and Arctic waters aren’t so friendly.
Warming ocean patterns, however, appear to be changing how much algae makes its way into the North Pacific. Bering Sea shelf waters have risen by as much as 3 degree Celsius in the last 10 years, the report says, and a patch of warm water crept through the Gulf of Alaska in 2015.
Sea ice plays an additional role. Warming, ice-free waters allow more algae-friendly sunlight into the sea, and open shipping lanes through the Arctic. Cargo vessels can transport algal species into new waters through ballast water discharge.
Several events in 2015 served as a prelude to the release of the NOAA study. The warm Gulf of Alaska water known as “the Blob” allowed a massive red algae bloom to move north from Pacific Northwestern waters. The algae led to toxin scare. Marine scientists at the time attributed no deaths to increased levels of algae toxins, but did see an increase in toxin levels in shellfish.
Researchers and fishermen haven’t positively connected anything sinister to the warm water, but it coincided with an unusual mortality event, the kind 40 percent of which Lefebvre said are caused by algal toxins.
Dead whales cropped up near Kodiak, Chignik, Katmai, Seldovia, and False Pass during the summer, along with dead sea lions in Dutch Harbor and Amalik Bay. Dead puffins and other seabirds abounded along the Gulf, as well as washes of dead baitfish including sand lances and herring.
“Those large whale die offs, we couldn’t get to them (to take samples),” Lefebvre said. “That investigation is still ongoing.”
The study will continue. The next step is to analyze temperature variations, sea ice composition, and a host of other factors against the presence of algae toxins and link the two in a predictive model. NOAA will also continue to monitor subsistence harvests.
• DJ Summers can be reached at firstname.lastname@example.org.