Sightings of freshwater jellyfish, or 'hydromedusae', in Canadian waters are becoming more common these days. Just yesterday, The Star reported on a man who had found one while he was fishing in Belmont Lake, about 60 km north of Trenton, Ontario.
These jellyfish, Craspedacusta sowerbyi, are an invasive species. They have a transparent or translucent 'bell', with a slightly white or greenish tinge, can grow to about 2.5 cm wide and have anywhere from 50 to 500 tentacles. The cells of these tentacles all contain cnidocysts - tiny organelles which recent research says can fire as quickly as 700 nanoseconds to inject toxins into the jellyfish's predators or prey.
Craspedacusta sowerbyi are native to the Yangtze River valley in China, and typically live in calm waters, such as those in reservoirs, lakes and quarries, as well as slow-moving rivers. They were likely brought to North America attached to plants and ships, and have been sighted in Quebec since 1955, and Ontario since 1980. They have spread throughout Lake Erie and Lake Huron, and were spotted in both Star Lake and Falcon Lake, in Manitoba in 2010.
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One potential reason for their spread is global warming or climate change. With the Yangtze River valley lying on roughly the same latitude as the southern United States of Georgia, Alabama, Mississippi and Louisiana, as temperatures rise it stands to reason that these creatures would move north to seek out waters with temperatures more comfortable for them. However, retired biology professor Terry Peard, who has more than 20 years experience studying freshwater jellyfish at the Indiana University of Pennsylvania, believes that the increase in sightings reported is also likely due to how easy the Internet has made it to submit those reports.
According to the Canadian Wildlife Federation and the United States Geological Survey, the impact of this species is unknown, although in a paper published in 2007, titled 'The invasiveness of an introduced species does not predict its impact', Dr. Anthony Ricciardi and Jill Cohen from McGill University identified Craspedacusta sowerbyi as a species which has "not caused substantial ecological impacts in their invaded range."
What is known, though, is that they are harmless to humans.
"I don't think it can penetrate human skin," says Peard. "We've handled them bare-handed for years, and we've never felt anything."
Sightings of freshwater jellyfish can be reported on Peard's website.