[USA] A review of more than 900 marine mammals hunted, stranded or captured for research along Alaska’s coast has found toxins from harmful algae in 13 species, creating concern that the natural poisonous substances could increase as water temperatures warm and sea ice diminishes.
Algal toxins were present in animals sampled from southeast Alaska to the Arctic Ocean. Researchers from the National Oceanic and Atmospheric Administration and other agencies examined feces, stomach content and urine for two toxins.
Algal toxin has led to deaths of sea lions documented since 1998 in central California. They have been found previously in Alaska, at times creating health concerns for people eating clams, but have not been documented to this extent, said Kathi Lefebvre, a research biologist for the National Oceanic and Atmospheric Administration.
“The real concern is that the waters are warming and the sea ice is melting and the light is more available, making it more favorable for these blooms of algae,” she said.
Algae are simple organisms, sometimes single-cell, that like other phytoplankton, float in the ocean at the mercy of ocean currents.
Harmful algae species produce toxins. When conditions are right, with optimal temperature and nutrients, harmful algae can grow rapidly divide and create dense blooms. They’re eaten by zooplankton or filter feeders such as clams, shellfish or tiny fin fish, allowing the toxin to move higher in the food web.
Lefebvre is program leader for NOAA’s West Coast Wildlife Algal-toxin Research and Response Network in Seattle, which looked at samples from 905 animals collected in Alaska wildlife over nine years. The sampling was “opportunistic,” meaning the same species of animal was not sampled regularly. That means the study could not detect whether toxins had increased in particular species over a decade, Lefebvre said.
Researchers looked for domoic acid and saxitoxin.
Domoic acid has killed California sea lions. A study last year indicated affected animals that survive can suffer brain damage that leads to significant deficits in spatial memory, which could affect their ability to forage, migrate or avoid ship strikes, Lefebvre said. Domoic acid was found in all 13 Alaska species reviewed and was found in 68 percent of bowhead whales samples and 67 percent of harbor seals.
Saxitoxin, which causes paralytic seafood poisoning in clams, was found in 10 of the 13 species. It was detected in 50 percent of the humpback whale samples and 32 percent of bowhead whale samples.
Researchers could not conclude whether algal toxins were related to 2015 Alaska marine mammal die-offs, such as fin whales and sea otters.
“We don’t have the smoking gun,” Lefebvre said. “We don’t have the right kinds of samples to look at.” Instead, the research emphasizes the importance and potential impacts of algal toxins in historically cold Alaska waters, she said.
Researchers also don’t know whether the toxin concentrations found were high enough to cause health impacts for the marine mammals sampled. They did conclude, however, that the levels accumulating in commonly eaten parts of the animals were not at a level of a concern for human safety.
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