Northwest Heat Hits Shellfish Hard

July 9, 2021

New York Times:

Dead mussels and clams coated rocks in the Pacific Northwest, their shells gaping open as if they’d been boiled. Sea stars were baked to death. Sockeye salmon swam sluggishly in an overheated Washington river, prompting wildlife officials to truck them to cooler areas.

The combination of extraordinary heat and drought that hit the Western United States and Canada over the past two weeks has killed hundreds of millions of marine animals and continues to threaten untold species in freshwater, according to a preliminary estimate and interviews with scientists.

“It just feels like one of those postapocalyptic movies,” said Christopher Harley, a marine biologist at the University of British Columbia who studies the effects of climate change on coastal marine ecosystems.

To calculate the death toll, Dr. Harley first looked at how many blue mussels live on a particular shoreline, how much of the area is good habitat for mussels and what fraction of the mussels he observed died. He estimated losses for the mussels alone in the hundreds of millions. Factoring in the other creatures that live in the mussel beds and on the shore — barnacles, hermit crabs and other crustaceans, various worms, tiny sea cucumbers — puts the deaths at easily over a billion, he said.

The dead sea stars, usually the most eye-catching creatures in tidal pools, hit him particularly hard. But the obvious mass victims were blue mussels, an ecologically important species that feeds sea stars and sea ducks and creates habitat for other animals.

Scientists have only begun to consider the domino effects. One concern is whether the sea ducks, which feast on mussels in the winter before migrating to their summer breeding grounds in the Arctic, will have enough food to survive the journey.

“It’s at least something that we’re starting to think about,” he said.

Species that live in intertidal zones are resilient, he noted, and the mussels on the shady north side of boulders seem to have survived. But if these extreme heat waves become too frequent, species won’t have time to recover.

While the heat wave over the Pacific Northwest has eased, punishing temperatures have persisted across much of the American West. Now, another heat wave appears to be building, only worsening the ongoing drought.

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