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California’s early June heat wave cooked coastal mussels in place

Eric Simons, BAY NATURE

Bodega Marine Reserve research coordinator Jackie Sones has worked in or walked on the rocky shores of the North Coast almost every day for the last 15 years. But while she was surveying the reserve for sea stars in mid-June, she saw something new: strips of bleached algae draped across the rocks, like frost, and a swath of dead mussels, hundreds or maybe thousands of them, black shells agape, orange tissue shining in the sun, stretching across 500 feet of rocky tidepools.

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

In all her time in Bodega Bay, she wrote in her blog The Natural History of Bodega Head, she’d never seen a mussel die-off that size, or affecting so many individual mussels.

She suspected immediately that the algae had bleached and the mussels had overheated earlier in the month. While many Bay Area residents fled toward fans or movie theaters or air-conditioned libraries to escape the record-breaking early June heat wave, the mussels, which attach themselves to rocks with super-strong threads and never look back, would have just roasted in place. The air temperature in Bodega Bay on June 11 hit an unusually warm 75 degrees Fahrenheit. The normal June sea breeze disappeared. A series of mid-day low tides stranded the tidepool animals out of the water for hours while the sun beat down from high overhead.

“In the past we’ve seen patches die, but in this case it was everywhere,” Sones said. “Every part of the mussel bed I touched, there were mussels that had died.”

She went back to the lab and talked to BML marine biologist Eric Sanford, who had seen the same thing in the part of the reserve where he’d been working. The next day Sones walked a longer stretch of shoreline, covering about a quarter-mile, and still saw the same pattern of mussel death. Further reports came in of die-offs around Bodega Bay at Dillon Beach and Pinnacle Gulch, at Sea Ranch, and at Kibesillah Hill north of Fort Bragg.

Northeastern University marine ecologist Brian Helmuth, who studies the effects of air temperature on marine creatures, said that on a 75 degree Fahrenheit day, the tissues inside a marine creature glued to a rock out of the water might rise to 105 degrees. The animals try to vent the heat building up inside of them but can’t without a breeze to carry it away. The mussels’ black shells trap even more heat. “They were just literally cooking out there,” Helmuth said. “Unfortunately this was the worst possible time.”

Read more at https://baynature.org/2019/06/26/californias-early-june-heat-wave-cooked-coastal-mussels-in-place/