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Lakes in the Canadian Shield are slowly becoming “jellified,” a legacy of acid rain that changed the water chemistry and has made life easier for a tiny crustacean with a big jelly blob on its back.

In the granite hills of Algonquin Park and the Gatineaus, lakes are low in calcium to start with.

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The acid rain years washed away much of the calcium in the lakes and surrounding soil, says biologist John Smol of Queen’s University.

And this tips the balance away from a little crustacean that normally lives in this lakes, called Daphnia, and lets another one called Holopedium take its place.

Holopedium needs less calcium. Both animals are sometimes called water fleas.

“This we think is quite major,” Smol said. “It’s a legacy of acid rain. This was a very slow problem, really under the radar.”

Holopedium carries a bulbous coating of jelly, possibly a defence against predators.

Photo by Ron Ingram, Ontario Ministry of the Environment and Climate Change / Ottawa Citizen

The ecological problem is that Daphnia is an important part of the food web in lakes. But a lot of water species can’t eat the bigger jelly-coated flea.