How heat waves distort ecosystems

Bleached kelp on San Juan Island, Washington during this summer’s heat dome. (Courtesy of Robin Fales)

During this summer sweltering heat wave, Robin Fales patrolled the same stretch of shoreline on Washington’s San Juan Island every day at low tide. The stench of decaying sea life increased as temperatures hit triple digits – around 30 degrees above average – and Fales watched the kelp beds she studies wither and fade. “They bleached more than I had ever seen,” recalls Fales, who holds a doctorate. candidate and marine ecologist at the University of Washington. She didn’t know if they would make it.

Never in recorded history had the Pacific Northwest experienced anything like the “heat dome” that plagued the region in late June 2021. Temperatures hit a searing 116 degrees Fahrenheit in Portland, Oregon, and 121 degrees at Lytton, British Columbia – the highest on record north of the 45th parallel.

Scientists said the event would have been “virtually impossible” without climate change. It killed hundreds of people, damaged roads and power lines and devastated crops. It has also caused widespread ecological fallout, the full extent of which scientists have not yet grasped.

Early reports were sobering: a billion crustaceans and other intertidal animals cooked to death on the British Columbia coast. The Portland Audubon Society declared a “hawkpocalypse” as it treated dozens of sick and injured birds. And in eastern Oregon, state officials have estimated that tens of thousands of groundfish sculpins have perished in streams already strangled by drought.

“They whitened more than I had ever seen”

By fall, the headlines and memories had faded, but the effects of the heat wave linger. In fact, researchers have learned that short periods of high temperatures can pose a greater threat to plants and animals than long-term warming, and may even increase the risk of extinction.

In a recent study, researchers looked at 538 species from around the world, nearly half of which had already become extinct in at least one place. They found that the doomed populations experienced larger (and faster) increases in maximum annual temperature than the others. Surprisingly, however, they often experienced smaller changes in average temperature, said John Wiens, an evolutionary ecologist at the University of Arizona and co-author of the study. “The most important variable is these hottest summer temperatures.”

Extreme heat can kill organisms instantly, especially if they are also exposed to intense sunlight. Dehydration sets in and organs fail as enzymes stop working and proteins suffer damage. Trauma can make survivors more vulnerable to disease and predation and reduce or delay reproduction. Hot weather can also cost animals dearly by discouraging them from foraging or hunting. And these events are happening more often: by 2040, heat waves are expected to become 12 times more frequent than in a non-warming world.

After the latest episode in the Pacific Northwest, researchers began tracking damage to a variety of species and ecosystems, such as coastal forests, which did particularly poorly. Scorched leaves have turned hillsides into sickly shades of orange, and already drought-stressed trees have dropped their needles prematurely. But the deadliest impacts may be invisible, said Christine Buhl, an entomologist with the Oregon Department of Forestry: Thirsty trees, for example, may have suffered damage to their roots and vascular system if they don’t could not extract enough moisture from the soil. “We’ll know for years to come how bad it was,” Buhl said.

“You can still go around and find the legacy of this event”

Australia provides a grim picture. After a series of heat waves hit the west of the country in 2010 and 2011, scientists documented widespread tree death, among other impacts, which later contributed to beetle outbreaks and wildfires, a said Joe Fontaine, a fire ecologist at Murdoch University in Perth. Even now, he said, “you can still shop around and find the legacy of this event.”

Yet heat waves can also help species adapt to long-term warming by driving rapid evolutionary change, said University of Washington climate change ecologist Lauren Buckley. They can weed out unfit individuals, giving an advantage to those who tolerate warmer temperatures. Scientists have seen evidence of such changes in Douglas fir and fruit fly populations. But “there’s kind of a middle ground,” Buckley said, between a stress test and a slaughter.

It’s too early to tell if the recent temperature spike has hit the sweet spot for some Northwest species, if any. On San Juan Island, however, Fales found some hope. After the heat wave, Fales studied the damage to the kelp she studies and determined that although it had lost about half of its biomass, most of the plants were still alive. Many mussels also survived.

This may be because warm spring temperatures prompted them to mount defenses before the heat wave, Fales said, by producing heat shock proteins that repair other damaged proteins, for example. But there’s another possible factor: By heavenly chance, summer low tides on the island always occur at midday, exposing intertidal organisms to peak temperatures and making it “a hot spot,” Fales said. . Perhaps the kelp and its neighbors had already begun to adapt.

This story was originally published by High Country News and is republished here with permission.