Canada is home to some of the most beautiful lakes in the world, but many of them are at risk of “jellification,” according to a paper published today in The Proceedings of The Royal Society B.
The study’s authors, led by ecologist John P. Smol, found that over a century of industrial pollution has leached lakes of calcium. In particular, acid rain and deforestation have been major drivers of this decalcification, which Smol called “aquatic osteoporosis.”
“For thousands of years, it was kind of in balance,” Smol told me over the phone. “Then acid rain came along—this uncontrolled experiment. It was a bit like putting vinegar on an Alka-Seltzer tablet. For a little while, whatever calcium was there would have been released very quickly, so for a short while, lakes would have had high calcium. But eventually, the easily removable calcium was washed out.”
Lumbering also contributed to this rapid loss of lakeside calcium. “If you cut down a tree and you let it rot there, the calcium goes into the lake. It just recycles,” said Smol. “But if you cut down a tree and put it in your house, you’ve removed that calcium and brought it to your house.”
Because calcium is such a crucial nutrient in food webs, its absence gives calcium-poor microorganisms an adaptive edge over competitors that require a lot of calcium. In this case, decalcification led to an ecological war between two planktonic water flea species: Daphnia and the jelly-coated Holopedium. Guess which one is responsible for the recent jellification of lakes.
“[Holopedium] has all this jelly, so it doesn’t need all this protection of a calcified exoskeleton. They have a big advantage now that the calcium’s lower,” Smol said. “Daphnia, these keystone water fleas, were disappearing because they had high calcium requirements.”
The rise of Holopedium has unleashed a death-by-1,000-cuts type of fate upon Daphnia. Not only are daphniids unable to subsist on withering calcium reserves, they are also targeted more by predators put off by Holopedium’s jellified exteriors.
“A lot of things can’t eat these jelly-clad fleas,” explained Smol. “They are about 10 times bigger because they’re encased in this jelly. They are too big and too non-palatable to be eaten by many organisms. Also, the food quality of Holopedium is much lower, so it can have far reaching ecosystem effects.”
Larval midges are among the many predators that refuse to dine on Holopedium, but love to feast on Daphnia—in fact, they are its main predator. As if that weren’t enough of a run of bad luck for Daphnia fleas, climate change is also reducing oxygen deep in lakes, which provides better breeding conditions for midges.
“It’s a multiple stressor world,” Smol said, “and it’s almost been a perfect storm for these organisms.”
It’s also not a Canadian-only issue. Though the 80 lakes Smol’s team studied were primarily in Ontario and Nova Scotia, Holopedium are thriving in calcium-depleted regions all over the world.
“The same types of issues are probably happening throughout New England,” said Smol. “There’s also reports of Holopedium in the Pacific Northwest. Scandinavia is another area with similar types of lakes and similar types of stressors.”
The displacement of daphniids by Holopedium also has repercussions beyond ecological disruption. The large jelly clumps holopediids form in lakes could potentially clog water intake valves.
“Just in Ontario, about 20 percent of our water intake for drinking water are from low calcium areas, so that could be a factor,” said Smol, who also pointed out the aesthetic problems inherent in finding gross clumps of gelatinous goo floating around lakes and washing on beaches.
There are no easy answers when it comes to restoring the ecological balance between the two water fleas, and between calcium-poor and calcium-rich organisms more generally. “It may take thousands of years to return to historic lake water calcium concentrations solely from natural weathering of surrounding watersheds,” said co-author Andrew Tanentzap in a University of Cambridge statement.
“In the meanwhile, while we’ve stopped acid rain and improved the pH of many of these lakes, we cannot claim complete recovery from acidification,” he added. “Instead, we many have pushed these lakes into an entirely new ecological state.”
So if the toxic algae bloom in Lake Erie wasn’t enough of a reminder to remain hyper-vigilant about lake pollution in the future, let the prospect of invertebrate jelly clumps floating around our lakes refresh our collective memory.