Mussels roasted to death in record-breaking California heat, experts say

A heat wave that sizzled much of California last month appears to have taken a devastating toll on a sea creature that is foundational to the marine ecosystem.

Jackie Sones, research coordinator for Bodega Marine Reserve north of San Francisco, said she saw hundreds or even thousands of dead mussels along the rugged Northern California coast after unusually hot temperatures cooked them to death, Bay Nature magazine reported in late June.

“It’s one of the first things you see, coming down the rocks into the middle of the intertidal zone,” Sones said, according to the magazine. “They were very visibly dead.”

Sones called it “a significant die-off of California Mussels” in a blog post published on June 18, adding that “a large percentage of the mussels were open and gaping, some were empty and some still had tissue inside.”

In a second blog post about the die-off the next day, Sones wrote that “we think this is the most significant mussel mortality we’ve seen on Bodega Head during the last 15 years … in terms of number of individuals and the amount of area impacted.”

Sones, who has worked on Bodega Bay for more than a decade, said she found tens of thousands of mussels roasted to death on the coast as she surveyed more, CNN reports.

Temperatures in notoriously temperate San Francisco hit 97 degrees during the mid-June heat wave, the Sacramento Bee reported, while in Bodega Bay the temperature hit 75 degrees — hot enough that the insides of mussels attached to the rocks and exposed to the hot air could swelter to 105 degrees, according to Bay Nature.

“They were just literally cooking out there,” said Northeastern University marine ecologist Brian Helmuth, according to the magazine.

Mussels won’t be the only creatures to suffer from the die-off.

“Mussels are known as a foundation species. The equivalent are the trees in a forest — they provide shelter and habitat for a lot of animals, so when you impact that core habitat it ripples throughout the rest of the system,” Sones said, according to The Guardian. “I would expect that this actually impacted the entire region, it’s just that you would have to have people out there to document it to know.

Back in 2004, a similar die-off struck the Bodega Head area that Sones studies — but Sones and Christopher Harley, a University of British Columbia biologist who studied the earlier incident, think this die-off is likely larger, according to The Guardian.

“These events are definitely becoming more frequent, and more severe,” Harley said, according to the British newspaper. “Mussels are one of the canaries in the coal mine for climate change, only this canary provides food and habitat for hundreds of other species.”

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Jared Gilmour is a McClatchy national reporter based in San Francisco. He covers everything from health and science to politics and crime. He studied journalism at Northwestern University and grew up in North Dakota.