seaweed_kitsilano beach_June 2022

B.C.’s sea life is bouncing back, slowly, after the 2021 heat dome

Barnacles are making a return, but one scientist says his early estimation that a billion creatures died from record-high temperatures was too low

It’s been just over a year since a devastating heat wave settled over British Columbia. It was in late June 2021 that temperatures so extreme, so unlike anything experienced here before, wreaked havoc across the province.

Those without easy access to air conditioning struggled to keep cool. Hundreds, mostly elderly people already burdened by health issues, died. A fire wiped out the village of Lytton. In farmers’ fields, crops wilted and berries shriveled on the vine. And, on coastal shorelines, barnacles, mussels and other sea life roasted under the powerful rays of the midday sun.

Twelve months ago, Chris Harley, a professor in the University of British Columbia’s zoology department, estimated that more than a billion sea creatures had died under the heat dome. 

A year later, Harley said the toll was far greater than he first thought.

“We get to numbers higher than [a billion] just estimating for one species of barnacle in the Strait of Georgia,” he told The Narwhal. “So that wouldn’t include all the clams and mussels and what was happening in Puget Sound or further north.”

The extent of the loss of crustaceans and bivalves — like clams, mussels and oysters — alone is striking, more so when the ripple effects are considered. Barnacles create vital habitat for other sea creatures. Mussels and oysters offer food not only for marine life, but people too.

For millennia, the ocean has been a source of sustenance for coastal communities. But warmer average temperatures and extreme heat waves could see rich sea life chased from some areas of the intertidal zone — the stretch of coastline inundated by water at high tide and exposed to sun and air at low tide. If that happens, there could be consequences for both food security and water quality.

Today, life is returning to areas scorched by last year’s unprecedented heat wave. The die off was patchy and the plants and animals in the intertidal zone that survived the heat wave “are the parents to the next generation,” Harley said.

“We have just tons of wee baby barnacles coating the rocks right now, so that’s encouraging,” he said. The crustaceans “make an incredible number of babies and those babies swim around a pretty good distance before they land.”

Barnacles are seen on a boulder at Kitsilano Beach.
Barnacles are seen on a boulder at Kitsilano Beach in Vancouver. Baby barnacles have been among the first sea creatures to return to intertidal areas after more than a billion of crustaceans and bivalves were wiped out during an unprecedented heat wave in the Pacific Northwest last year. Photo: Ainslie Cruickshank / The Narwhal

But the mussels that were lost haven’t yet returned, he said. Neither have seaweeds, which can’t travel as far as baby barnacles. “So, if they’ve been knocked out on a shore, it just takes longer for them to re-establish,” he said.

Barring another major heat wave, the shorelines should look more like they did in 2020 in just a few years. “Even if it gets a little bit hotter later in the summer, having a cool spring was a big advantage,” Harley said. “Hopefully, we’ll see that play out as an accelerated recovery.”

But another period of extreme heat could threaten that renewal.

Location determines impact of heat wave on intertidal life in the Pacific Northwest

Before the heat wave struck, Amelia Hesketh, a researcher in Harley’s lab at the University of British Columbia, had coincidentally set up an experiment to test how exposure to direct sunlight affects survival of sea life in the intertidal zone.

Hesketh studies sessile invertebrates — animals like barnacles and mussels that can’t move, and form critical habitat for other organisms. Critters that may be dislodged by waves, for instance, often take shelter in the gaps of a mussel bed.

Hesketh initially set up her experiment to better understand the thatched barnacle, which grows mostly in the Victoria area. It’s pretty big as far as barnacles go and looks like a “little haystack,” she says. 

Some people might not describe them as “cute,” but Hesketh does. She wanted to know what organisms live in thatched barnacle beds and how they are affected by temperature.

“In the summer, in the Strait of Georgia and Strait of Juan de Fuca, the low tides often occur during the middle of the day,” she said. “So, things are exposed to the hottest temperatures of the year.”

On a section of Victoria coastline, Hesketh set up a series of shades, intending to compare how shaded barnacle beds fared relative to their unshaded counterparts.

It was a passion project, really. Until the heat wave.

Amelia Hesketh, a research at the University of British Columbia stands in the intertidal zone at low tide on Kitsilano Beach with the ocean behind her and tanker ships visible in the distance.
Amelia Hesketh, a researcher at the University of British Columbia, had coincidentally set up an experiment to test how exposure to direct sunlight affects survival of sea life in the intertidal zone before the heat dome hit. Shaded barnacle beds had much higher survival rates than those that weren’t shaded. Photo: Ainslie Cruickshank / The Narwhal

Climate scientists with the World Weather Attribution initiative, which assesses the role climate change plays in extreme weather events, determined that the 2021 heat wave in North America’s Pacific Northwest would have been “virtually impossible without human-caused climate change.”

In a study published this spring, researchers from the United Kingdom looked at a region covering northern Oregon, Washington and southern B.C. and found the average temperature on the hottest day during the heat wave — June 29, 2021 — was 39.5 C. Many areas saw temperatures exceed 40 C. 

A graph showing daily high temperatures for the last week of June and first week of July in a region covering northern Oregon, Washington and southern B.C. from 1950-2021. The temperatures for 2021 are shown in red.
A comparison of daily high temperatures in a region covering northern Oregon, Washington and southern B.C. The last week of June and first week of July in 2021 are shown in red, with black showing daily highs between 1950 and 2020. Graph: Reprinted with permission from Thompson et al., Science Advances 8 (2022)

In the decade before the heat wave, the average daily temperature in the region during the months of June, July and August was 23.4 C.

As the heat dome retreated and temperatures returned to something more like normal, Hesketh returned to the site of her experiment.

At first, she didn’t realize so many barnacles had died. Many of the plates covering the openings in their shells that they feed through were still intact. It was the smell that gave it away. When she poked through those protective plates, Hesketh said the barnacles were “limp” and “rotting from the inside.”

“It was a sad day to be an ecologist,” she said. “This year has been an interesting process of sort of coming to terms with what that ecosystem will look like in the future.”

But not all the barnacles had died. The shades had made a difference.

“It was a pretty stark contrast,” she said. “In some spots, 100 per cent of barnacles were gone and then underneath shades, they were pretty much all alive.”

In the same way that Hesketh’s shades protected some barnacle beds from the worst of the scorching heat, some sea creatures found refuge under the blades of kelp growing in the intertidal zone, Rebecca Hansen, who also works in Harley’s lab, told The Narwhal.

Rebecca Hansen, standing, and Amelia Hesketh, both researchers in Harley's lab at the University of British Columbia, examine marine life on a boulder at Kitsilano Beach during low tide.
Rebecca Hansen, standing, and Amelia Hesketh examine marine life on a boulder at Kitsilano Beach during low tide. While life is returning to intertidal areas, it could take a few years before it’s back to the way it was before the heat dome. Photo: Ainslie Cruickshank / The Narwhal

Barnacles, mussels and seaweed living on northeast-facing shores or even the north face of boulders also fared better than sea life that was more exposed to the sun.

A new study in the scientific journal Ecology suggests that animals farthest from shore fared better as well. Based on observations from more than 100 different sites, the study states that “species found higher in the intertidal, such as acorn barnacles, were generally found in worse condition than species found lower in the intertidal such as clams and oysters.” 

But the extreme heat challenged species in deeper water too. William Cheung, a professor at the University of British Columbia’s Institute for the Oceans and Fisheries, uses computer simulations to predict the impacts of heatwaves on fisheries in the northeast Pacific ocean, off the coast of B.C and Alaska.

While the effects will vary between species and regions, Cheung said salmon — sockeye in particular — will be among the most affected by warming temperatures.

“Sockeye salmon is a cold adapted species and so they prefer cooler waters,” he said. Hotter temperatures can affect their food supply in the ocean, potentially limiting their ability to grow, Cheung explained. Sockeye may also struggle to reach spawning grounds in warmer waters.

Cheung’s modelling projects that climate change could reduce sockeye salmon populations, many of which are already threatened, by 30 per cent or more over the next couple of decades.

With the added burden of more frequent and intense heat waves, though, the impact on populations could be twice as bad.

Intertidal habitat expected to shrink as climate changes, but Indigenous Knowledge could help

As climate change leads to hotter, drier summers, intertidal species may see their habitat shrink.

Hansen is currently collecting data to measure shifts in the habitat range of intertidal kelp at sites between Victoria and Port Renfrew, on the southern stretch of Vancouver Island. She’ll compare her findings against historical data that goes back decades.

Preliminary data indicates the upper extent of kelp habitat at two sites has shifted farther away from shore, lower in the intertidal zone, than it was even 10 years ago. Essentially, species that make their home in the intertidal zone are seemingly being squeezed into a smaller area, Hansen explained.

Amelia Hesketh, a PhD candidate at the University of British Columbia, points out barnacles on a rock in the intertidal zone at Kitsilano Beach.
“We have just tons of wee baby barnacles coating the rocks right now, so that’s encouraging,” UBC professor Chris Harley said.

On top of broader warming trends, climate change is expected to cause more frequent and intense heat waves. That’s worrying, since the longer term impact of extreme events such as the heat dome depends in part on how often they occur.

“If this sort of thing happens once every 20 years, it will be very noticeable and it will smell terrible and there will be some temporary disruptions in the ecosystem — but it should bounce back,” Harley said.

If, however, extreme heat waves happen more often, even once every five years, “we might start to lose some of the species that just can’t recover enough in the intervening years to maintain their populations,” Harley warned.

And that could have consequences for food security.

“Oyster growers, some of their oyster crop is grown directly out on the beaches,” he said. “That’s even more true for clams, like cockles, and we lost an awful lot of cockles during the heat wave.”

People that rely on clams for food or income “have legitimate reason to be worried,” Harley said.

In the southern Gulf Islands, members of the W̱SÁNEĆ Nations and the Cowichan Nation Alliance are leading the restoration of sea gardens that were tended for thousands of years, fostering the growth of important foods such as clams.

These gardens were in shared territory and people from nations in the north and south would travel there to harvest clams as well as seaweed, according to Nicole Norris, an aquaculture specialist and knowledge holder from the Halalt First Nation.

Sea gardens, which are also known as clam gardens, tend to include a rock wall in the lower part of the intertidal zone that traps sand and sediment behind it. 

“It creates a grocery store,” Norris, whose ancestral name is Ala̱g̱a̱mił, told The Narwhal.

By changing the slope of the beach, the wall can increase the intertidal zone for clams, she explained.

But “there’s no sense in restoring a wall if we’re not touching the beach,” she said.

Norris said there’s value in “fluffing” the beach, which means using a potato rake to turn over the substrate in a process akin to tilling a garden. It helps loosen the top layer of silt and draws the grainy substrate to the surface, making it easier for clams to move around, Norris said. Fluffing could make it easier for species like butter clams, which tend to burrow in the sand, to retreat from the glare of a hot sun into the sediment.

“The government came in and said ‘wow, these are some really nice spaces, we’re going to draw an imaginary line around this and we’re going to call that protection,’” she said.

“Meanwhile, what they did is they killed those viable food sources by not allowing us to interact and actively manage those spaces,” she said.

Now, Norris and others are teaching the next generation how to care for and tend to the sea gardens. At the same time, the work is helping to revive the Hul’q’umi’num language, she said.

“We teach by showing,” Norris said. “When we’re on the beach, the Elders run their hand across the beach and they say ‘pqwutsun’ ” — pronounced “pa-qwut-sun,” meaning sand.

Already, life is returning to these spaces because of the work Norris and others are doing. “It’s phenomenal,” she said.

While preventing the worst effects of climate change will require a dramatic reduction in greenhouse gas emissions, restoring and tending to sea gardens could make clams in those areas more resilient to extreme heat events. 

“I’m sure that if we were there more often, we could definitely create a sustainable food source,” Norris said.

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The Narwhal’s reporting team is busy unearthing important environmental stories you won’t read about anywhere else in Canada. And we’ll publish it all without corporate backers, ads or a paywall.

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