Algae have changed dramatically in Great Slave Lake — and what that means for fish is uncertain

Algae growing in Canada's deepest lake have changed dramatically in the past couple of decades according to new study — and although one researcher considers the new microscopic organisms to be "beautiful" he says it's "definitely" going to have repercussions for the rest of the food chain. 

John Smol, a biology professor at Queen's University in Ontario and a co-author of the study, said around the turn of the 21st century, a small-celled type of algae replaced the larger type of chain-forming algae that used to be dominant in Great Slave Lake in the N.W.T.

"We're quite surprised how striking the change was," said Smol, who's studied algae for more than four decades.

Smol attributes the "very sharp transition" to climate change, which is warming the Arctic and sub-Arctic more quickly than other parts of the world. There's less ice cover on Great Slave Lake, he said, meaning the water is getting warmer and more light is filtering into it.

The small-celled planktonic diatom algae that have replaced the chain-forming diatoms do better under these conditions, said Smol. The sheer amount of algae in the lake are also increasing because more light means more photosynthesis — fostering growth. 

"Most people say 'who cares,'" said Smol. But, he pointed out, any change at the bottom of the food chain is going to lead to changes above it — rippling through invertebrates to fish and the animals and people that eat those fish. 

The peer-reviewed study, published in Proceedings of the Royal Society B on Tuesday evening, said the algal change between the late 1990s and the mid 2010s represents a "new ecological regime" in Great Slave Lake.

Kathleen Rühland, the study's lead author and a senior scientist at the Paleoecological Environmental Assessment and Research Lab, said in a media release that big shifts like this are a "sure sign that the entire lake is changing and changing fast." 

It will have "unknown consequences for aquatic ecosystem functioning and fish populations that First Nations, Métis and other northern communities rely on," wrote Marlene Evans, another co-author of the study and a research scientist with Environment and Climate Change Canada.

Andrea Kirkwood, an algal ecologist at Ontario Tech University in Oshawa, Ontario, was not involved in the study — and isn't surprised by its findings. 

"I view this study as another important piece of evidence showing the ecological effects of climate change," she said. "There's definitely a tight association between the changes in the [algae] community and climate." 

Kirkwood described Smol and the lab where the research was conducted as "world renowned." 

Charlie Trick, a professor in the Department of Health and Society at the University of Toronto who has also studied algae and wasn't involved in the study, spoke highly of the research too, saying it is "very calmly written" and it doesn't "over-state" its findings. 

"You've got the best of the best, doing a really good job, giving you a cautious report," he said.