The phrase "hot enough to fry an egg on the sidewalk" is oft met with rolled eyes and accusations of exaggeration. But this past month, California shellfish experienced temperatures so hot that such a phrase may not be hyperbolic.

In June, temperatures at Bodega Bay in northern California reached in excess of 100 degrees Fahrenheit. That was hot enough to cook local mussels inside their shells.

The mussels — firmly stuck to coastal rocks, where they feed on plankton floating in the sea water — are exposed at low tides to the scorching sun. According to a research coordinator at Bodega Bay marine reserve, Jackie Sones, this month a California heat wave roasted these shellfish where they sat.

Sones told The Guardian about "scores of dead mussels on the rocks, their shells gaping and scorched, their meats thoroughly cooked;" it's the largest die-off of mussels in at least 15 years at this location.

And it might not be just Bodega Bay, a picturesque inlet on the coast of California's wine country. Sones reported that other researchers told her about similar mass mussel deaths up and down 140 miles of the state's coastline.

Rippling effects of heat waves and warming temperatures

This isn't the first time mussels have roasted en masse. In 2004, a biologist at the University of British Columbia, Christopher Harley, reported a similar incident, though he and Sones think this year's die-off is likely worse.

Bodega Bay temperatures were hot enough to cook mussels inside their shells. Arnstein Rønning/Wikimedia Commons

"These events are definitely becoming more frequent, and more severe," Harley told The Guardian. "Mussels are one of the canaries in the coal mine for climate change."



Last year was the warmest year on record for the world's oceans, and the fourth warmest for the planet itself. A trend of rising global temperatures — in part due to human-driven climate change — can be linked to changes in other species, and the wider spread of diseases, as well as the occurrence of severe heat waves like the one baking Europe this week.

Warming temperatures not only cook mussels inside their shells, but also precipitate climates where flesh-eating bacteria can spread farther, faster in US waters.

The bacteria, Vibrio vulnificust, thrives in warm salty or brackish water. It can cause a flesh-eating disease that can sometimes result in amputations or death. People can contract a Vibrio infection after wading in this water with an open wound or eating raw shellfish from the water.

Read More: A 12-year-old girl got infected with flesh-eating bacteria on a Florida beach. Experts say this will become more common as ocean water warms.

And it's not just flesh-eating bacteria. As average temperatures rise around the world, the geographic area in which disease-carrying mosquitoes can thrive and transmit illnesses like the Zika virus and dengue fever is expected to grow.

According to a March 2019 study, if greenhouse gas emissions continue to rise unabated, nearly 1 billion new people will be exposed to two species of disease-carrying mosquito over the next 60 years.

Europe, the US, and Canada, in particular, will see increased exposure.