Months after mass die-off of sea creatures in B.C. heat dome, researchers return in search of signs of life

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At the height of B.C.'s heat dome in June of 2021, Chris Harley, a professor at UBC's Department of Zoology, headed to West Vancouver's Lighthouse Park to measure water temperatures and observe how the marine animals that inhabit B.C.'s coastlines were faring under the extreme conditions.

He anticipated seeing some degree of die-off, but instead was greeted with the overwhelming stench of rotting flesh as sea creatures cooked in the open air, their shells popping open.

In the days that followed, Harley and his students estimated that billions of sea creatures died as temperatures soared above 40 C, and water temperatures reached as high as 56 C.  

Ten months after the catastrophe on B.C.'s shores, the researchers have returned to comb B.C.'s beaches, checking for signs that the vital populations of seaweed, crustaceans and shellfish native to the coast are seeing a resurgence. 

"There are some reasons for optimism. Seeing the wee little juvenile barnacles coming in is a good sign. But the system has been disrupted," said Harley, who has studied shorelines on the West Coast since 1995.

"Yesterday I was down closer to White Rock and it still looks like a bomb has gone off down there — lots of death and destruction."

Harley said while the ecosystem is showing promising signs of resilience, it is now uniquely vulnerable to the dangers of another heat dome. And the collapse of even one population has cascading effects on others. For example, many of the rocks usually slicked green and brown with seaweed are now bare, leaving the baby barnacles exposed to the sun. 

"Once all the species are back, we know that a diverse ecosystem is more resistant to that sort of insult. But if you get another big disturbance, another big heat wave before the ecosystem has a chance to recover, that can actually do more damage than it would have otherwise," said Harley.

Harley and his students have studied the coastlines from Victoria to Sooke and White Rock, and as far north as Bamfield, Puget Sound, and the Strait of Georgia. They measure the number of sea creatures repopulating by conducting random quadrant searches — laying down a square and counting the creatures that fall inside it, then scaling up to estimate mortality.

Early findings indicate species with mobility had a higher survival rate, thanks to their ability to find shade and cooler enclaves. But those anchored to rocks, like starfish and shellfish, fared worse. Barnacles and muscles planted on the north sides of rocks often survived, while those on the south side of the rock are, in many places, entirely gone.

Harley warns B.C.'s beaches and waters will transform if species like mussels and barnacles are replaced by populations that thrive in warmer temperatures.

"Mussels and barnacles filter out a lot of the gunk in the water. What would False Creek look like if we lost those filters or replaced them with something that might work a little bit differently? There are questions that we hadn't even thought to ask prior to last summer, because we weren't expecting this sort of thing to happen this quickly," he said.