'Cooked to Death': Heatwave Probably Killed More Than a Billion Marine Animals on Canada’s Coast

Jul 9

Experts estimate that nearly a billion mussels, clams, sea stars and snails died along the Salish Sea coastline due to record-breaking temperatures.

Dead mussels on the coastline. Credit: Christopher Harley

More than a billion marine animals along Canada’s Pacific coast may have died last week as a result of the record-breaking temperatures in British Columbia.

The unprecedented heat wave that hit western Canada and the north-western U.S. saw temperatures soar to record highs in late June and early July, killing as many as 500 people and triggering hundreds of wildfires, mainly in British Columbia.

Christopher Harley, a marine biologist from the University of Columbia, discovered ten of thousands of dead mussels, clams, sea stars and snails along the Salish Sea coastline, and estimated that more than a billion animals may have perished across the country.

Harley was “stunned” by the smell of rotting mussels and the sight of decaying snails, sea stars, and clams along a Vancouver-area beach.

“When you have a big die-off like this, the scavengers can’t eat them quickly enough to process all of that extra meat and so it just sits rotting in the sun,” he said. “So if you have been to a local beach in the past week or two and noticed that awful low-tide smell multiplied by 100, that’s the smell of all the animals that have just died.”

“It was an overpowering, visceral experience.”

As temperatures reached 40 C in Vancouver, Harley’s team used infrared cameras to record temperatures above 50 C along rocky shore habitats.

“It was so hot when I was out with a student that we collected data for a little bit and then retreated to the shade and ate frozen grapes,” said Harley. “But of course, the mussels, sea stars and clams don’t have that option.”

Animals found in the intertidal zone - an ecosystem found on marine shorelines - can withstand temperatures in the high 30s, Harley noted, but the scorching heat, combined with low tides created deadly conditions.

"A mussel on the shore in some ways is like a toddler left in a car on a hot day," Harley said. "They are stuck there until the parent comes back, or in this case, the tide comes back in, and there's very little they can do. They're at the mercy of the environment. And on Saturday, Sunday, Monday, during the heatwave, it just got so hot that the mussels, there was nothing they could do."

To gauge the scope of marine destruction, Harley multiplied the amount of dead animals found in small areas by the total habitat size in the Salish Sea: “You can fit thousands on to an area the size of a stove top. And there are hundreds of kilometres of rocky beach that are hospitable to mussels. Each time you scale up, the numbers just keep getting bigger and bigger. And that’s just mussels. A lot of sea life would have died.”

The marine deaths will also temporarily affect water quality, as mussels and clams help to filter the sea, Harley said. Other animals that rely on mussels for food, like starfish and sea ducks that migrate back and forth from Alaska, will likely experience repercussions of the die-off too.

Mussel bed populations will likely recover in a year or two, but these deadly heat waves may become more common and severe as a result of climate change, according to Harley. "Eventually, we just won't be able to sustain these populations of filter feeders on the shoreline to be anywhere near the extent that we're used to.”

Now, south-western Canada and the western U.S. States are bracing for another heatwave in the coming week.

“A lot of species are not going to be able to keep up with the pace of change,” said Harley. “Ecosystems are going to change in ways that are really difficult to predict. We don’t know where the tipping points are.”

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