As It Happens

Acid rain's legacy threatens crayfish to the verge of extinction in Algonquin Park

A new study by Canadian scientists warns of drastic declines in crayfish populations in Ontario's Algonquin Park to the point of extinction. The culprit: a lack of calcium in the water.
John Smol, professor of biology at Queen's University, was part of a research team looking at drastic declines in crayfish populations. On the right, is a Cambarus bartonii crayfish with its young, taken from Cradle Lake, Algonquin Park. (PEARL/Queen’s University/Robin Valleau/OMOECC)

Canadian scientists have released a new study on what they call "aquatic osteoporosis" and its drastic effect on declining crayfish populations and aquatic life in the lakes in and around Algonquin Provincial Park. 

The researchers found that depleted calcium levels have now driven some crayfish populations to near extinction.

"Crayfish are in decline in many parts of the world," John Smol tells As It Happens host Carol Off. "We were suspicious that one factor that may be causing the decline of crayfish in certain regions is the lack in calcium."

Close-up of Cambarus Bartonii crayfish from Clayton Lake. (Ron Ingram/Ontario Ministry of Environment and Climate Change)

​Smol is a professor of biology at Queen's University and one of the authors of the research. He explains that the bedrock in Algonquin is granite, not the calcium carbonate-rich limestone found in the southern regions of Ontario. Over time, the minimal calcium deposits in the granite have been drained to critically low levels in many lakes.

"It appears to be a legacy of acid rain," Smol says.

He says the pH levels are changing in many lakes but the calcium reserves are no longer present in the soil to replenish the lake.

Smol says crayfish have a particularly high calcium requirement because of their hard exoskeleton.  He adds that their extinction could cause a ripple effect with severe consequences on other aquatic species.

"These are actually a fairly keystone species. Crayfish are important because they eat plants but they're also detritivores. They are like the garbage collectors in lakes." Smol says the outlook is grim.
Traps ready for deployment in Pincher Lake, Algonquin Park. (Ron Ingram/ Ontario Ministry of Environment and Climate Change)

"We are dealing with a multiple stressor world, where all these things are additive."

Algonquin Park is the ideal setting to conduct the research. The remote location allowed Smol and his team to study regional stresses on the watershed rather than pulling data from a less controlled local area.

"There are so many reasons why different types of organisms like crayfish might be under decline but if you go to a place like Algonquin Provincial Park you can remove a lot of stresses. For example, road construction or agriculture or local activities."

Close-up of the Orconectes Propinquus crayfish. (OMOECC)

"We've been calling it colloquially '"aquatic osteoperosis" because as we all know we all need calcium," Smol explains. "At a certain point there's too little in the water for certain organisms to live."

Smol claims the only way to reverse the problem is to further decrease acid deposition which is an unrealistic fix.

"This calcium decline is really quite a wicked problem - it doesn't have an easy solution to it."


To encourage thoughtful and respectful conversations, first and last names will appear with each submission to CBC/Radio-Canada's online communities (except in children and youth-oriented communities). Pseudonyms will no longer be permitted.

By submitting a comment, you accept that CBC has the right to reproduce and publish that comment in whole or in part, in any manner CBC chooses. Please note that CBC does not endorse the opinions expressed in comments. Comments on this story are moderated according to our Submission Guidelines. Comments are welcome while open. We reserve the right to close comments at any time.

Become a CBC Member

Join the conversation  Create account

Already have an account?