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Toxic algae blooms raise the risk of fatal heart disease in sea otters

Toxic algae blooms raise the risk of fatal heart disease in sea otters. A neurotoxin produced by algae blooms is causing fatal heart disease in sea otters, according to a new study from UC Davis. Southern sea otters are inadvertently ingesting domoic acid by eating contaminated crabs and clams.

“Sea otters are an amazing indicator of what’s happening in the coastal environment, not just to other marine animals, but to us, too, especially on the issue of domoic acid,” said study senior author Christine K. Johnson is the director of the EpiCenter for Disease Dynamics in the One Health Institute.

Domoic acid is produced by harmful algal blooms and accumulates in the marine food web. In 2015, a massive warm water “blob” created a widespread bloom along the West Coast. Levels of domoic acid became so toxic that the Dungeness crab fishing season was forced to close.

The past five years are the hottest on record for the world’s oceans, which means that toxic algae blooms and domoic acid exposure will continue to rise.

To investigate the relationship between long-term exposure to domoic acid and fatal heart disease in southern sea otters, the experts analyzed data from 186 free-ranging individuals in California from 2001 to 2017. Of those otters, heart disease was listed as a cause of death for 34 of the 48 otters that died during that time.

The scientists found that otters who consume a high proportion of crabs and clams have a 2.5 times greater risk of fatal heart disease. Even southern sea otters who do not consume large amounts of crabs and clams have nearly double the risk of dying from heart disease as a result of exposure to domoic acid.

The researchers also that discovered domoic acid is particularly harmful to prime-age adult sea otters, whose survival is vital for population growth.

“That’s worrisome for the long-term population recovery of southern sea otters, which are a threatened species,” said study lead author Megan Moriarty. “This study emphasizes that domoic acid is a threat that isn’t going away. It’s a food web toxin and is pretty pervasive.”

Study co-author Melissa Miller, a veterinarian and pathologist with the California Department of Fish and Wildlife, recently led a separate study analyzing the causes of death of sea otters.

“Improving our understanding of the effects of domoic acid on the health and population recovery of southern sea otters is extremely important” said Miller. “Given their unique biology and specialized diet, sea otters are extremely vulnerable to toxic algal blooms, which are likely to worsen with climate change. So the results of this work have far-reaching implications.”

The study is published in the journal Harmful Algae.

By Chrissy Sexton, Staff Writer

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