Freshwater jellyfish are sticking around
Defensive mechanism allows the creatures to survive even a month spent in lab’s freezer
Are they invaders, or were they always here?
Researchers disagree, but one thing is sure: Their zombie-like indestructibility means freshwater jellyfish aren’t going anywhere.
It might not really matter, though — aside from startling a few swimmers every now and then with their oddly eerie presence, they’re unlikely to have a noticeable affect on ecosystems, the Ministry of Natural Resources and Forestry reports.
While freshwater jellyfish were first reported in Georgian Bay in the 1950s, it’s likely they were there for some time before they were first recorded, a spokesperson for the ministry said in a statement.
They’re considered an invasive species but, Ted Peard said, that’s “debatable.”
Peard is a retired biologist who studied freshwater jellyfish at the Indiana University of Pennsylvania and continues to run freshwaterjellyfish.org, where people across the U.S. and Canada can report freshwater jellyfish sightings.
“I haven’t been given a definitive answer by any agency, anybody I’ve talked to. That leads me to believe that they couldn’t have always been here. I just don’t know,” he said.
One line of thought puts their origin in the Yangtze River basin in China, Peard said.
They were discovered in England and Pennsylvania in the 1800s and the ministry said they likely travelled to Ontario on a boat.
“I don’t know if that’s how they got here or we always had them,” Peard said.
Sightings of the small, translucent medusas have been reported across Ontario from the St. Lawrence River, near Prescott, in the east, to Saganaga Lake near Thunder Bay towards the west and in many lakes and rivers in between, including Lake Ontario.
Earlier this month, a couple from Port Dover, Ont., came across one while fishing in Lake Erie.
Jeremy Stevenson was reeling his line in when he noticed what he thought was a piece of plastic in the waters.
“My girlfriend scooped it up with a little Tupperware thing and, it turns out, it was a jellyfish,” he said.
“He was only the size of maybe a loonie . . . just a tiny, tiny thing.”
It’s not believed that a freshwater jellyfish’s “stingy cell, the little barb that they shoot out to paralyze” their food, can penetrate human skin, Peard said.
They can be hard to spot, especially when the wind picks up, and they’re not strong swimmers so they’re at the mercy of the currents. But they are not going anywhere. “There’s no way to kill them,” he said. He’s not sure how they do it, but the polyp form of a jellyfish has a self-defence mechanism that even a month spent in a freezer during a lab experiment couldn’t destroy.
The polyp form is a cylinder shape that sits on the floor of a water body and spawns the free swimming medusa. When it senses that the water is too cold or that it’s drying up, it will “shrink down into a flat disk and just sit there.”
Some researchers think that may be one way freshwater jellyfish are spread — as flat, dried-out disks picked up by the wind and flown to new waterways.
“When favourable conditions return, they’ll rehydrate back into the polyp again,” Peard said.