Dead sand dollars and fragments of dead mussels rest on the sandy bottom of shallow water

Heat wave killed far more marine animals than originally thought, says scientist

UBC marine ecologist Dr. Chris Harley initially told the media that more than a billion mussels, clams, sea stars and other invertebrates may have cooked to death in the area between Campbell River and Washington state. That was a ‘back of the envelope’ estimate, based on his observations among the Lower Mainland’s mussel population and some preliminary reports. Harley has done a great deal more research since then. He now guesstimates that, conservatively speaking, the number of marine fatalities during last June’s heat wave is closer to 10 billion.  

Image credit: Dr. Chris Harley at Kits Beach, with downtown Vancouver in the background. -Photo by Chris Harley

In the attached podcast, he describes the new temperature records being set throughout British Columbia.

“Unfortunately for marine life, those really hot days coincided with very low tides. So things that aren’t normally out of the water for very long, were left high and dry during extreme hot weather,” explained Harley. “That combination resulted in dead sea stars, and dead clams, and dead mussels, and dead barnacles – the list just goes on and on.”

While it is easy to spot dead mussels because their shells open, this isn’t as easy with some other species. Harley says that for the first few weeks, there is very little to distinguish between live and dead barnacles. 


Dead barnacles on Calvert Island (between Port Hardy and Bella Bella) on 20 August 2021 Photo by Chris Harley

As the geographic extent of the disaster, numbers of species involved, and numbers of individual animals became clear – Harley gave up on the attempt to make an exact count.

In the Campbell River -Discovery Islands area

While there is not much information about the marine impacts, Harley said “the north end of the Straight of Georgia is one of the places that got the hottest for coastal communities.”

Visiting the area south of Comox, on Vancouver Island, Harley said, “There were certainly still a lot of dead barnacles in evidence as of a few weeks ago.”

There were die-offs on Quadra and Calvert Island, as well as Desolation Sound. 

Snails feasting on dead mussels at Smelt Bay on July 10, 2021 – Photo by Roy L Hales

A number of reports came from Cortes Island, and on July 10th Cortes Currents emailed Harley a series of photos of dead mussels at Smelt Bay. There appeared to be thousands. 

Snails were attached to some of the shells.

Harley responded, “Yes, you do have some snails in your photo. Those guys are apparently pretty tough – I’ve seen them on other beaches where other species didn’t make it through the heat wave. One of them in the upper-middle part of the second photo has glued itself on edge to a mussel shell with a little blob of mucus. They do that so that as little as possible touches a hot surface, which keeps them cooler.”

He suggested returning to the site to do a series of plots and put a metre stick in the images to indicate the scale.

Dead sand dollars and fragments of dead mussels in Sand dollar ‘Plot’ 4/20, July 14 – Photo by Roy L Hales

Most of the dead mussels had washed away by the time Cortes Currents returned to take 10 ‘plots’ on July 14th, but there were also what appeared to be thousands of dead sand dollars.

‘Wow!’ emailed Harley, looking through the subsequent images from 20 sand dollar plots.

Local biologist Deb Cowper reported that some sand dollars survived in the more sheltered waters of Mansons Lagoon, but Smelt Bay is more exposed. There do not appear to be any survivors in the images taken by Cortes Currents.

Most of the sand dollars were white, which Harley suggested meant they are ‘recently dead.” There were also some, ‘greenish ones have been dead long enough to acquire some algal growth.’ 

Dead sea star at Smelt Bay July 14, 2021 – Photo by Roy L Hales

Putting it in focus

Harley said he is aware of recent die-offs in California and New Zealand, but they were much smaller by comparison. 

“There are places that are just naturally hot, like Hong Kong, where every year when it gets hot – things just die. But those species have evolved in that system and essentially only live for a year,” he said. “That’s not the way species have evolved in British Columbia, so it is a bigger problem when things die-off here.” 

Harley is not aware of an intertidal die-off of this magnitude having occurred anywhere else in the world. 

“I would not be surprised if we see another heat wave like this in the next five or ten years because it is no longer a once in a lifetime event. This is the kind of thing that is going to happen more regularly. It is possible that the next one could be even more severe.” 

Cropped image of Dead kelp crab, along with dead dogwhelks (the snails) and barnacles, at 1001 Steps Park near White Rock – Photo by Chris Harley

Instead of becoming depressed, Harley hopes people treat the die-off as a call to action. 

He added, “There are small things that we can do to bend the curve of climate change like we’ve done for the COVID pandemic.” 

Top photo credit: Dead sand dollars and fragments of dead mussels rest on the sandy bottom at Smelt Bay during high tide – Photo by Roy L Hales

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