Small and harmless freshwater jellyfish are being found in record numbers in lakes as varied as the US East Coast to Manitoba, Canada.
Experts cannot explain the sudden presence of the freshwater jellyfish in lakes where local observers say they've never been seen before. The jellyfish species, C. sowerbyi came from Asia approximately 100 years ago, and are considered to be an invasive species because they are not native to North America. The unusual sightings of the invasive species have created a sensation in the communities where they have been found.
The jellyfish found in a lake in Whiteshell Provincial Park, Manitoba were thought to be a first for the province reported the Winnipeg Free Press. Authorities said they would study the species to determine what ecological impact they might have. However, another report from the Winnipeg Free Press said the species has been found in Manitoba before. The earliest sighting of the jellyfish in Ontario, also called 'Medusa,' was 1980.
The adaptable species has been found in a gravel pit in Lithuania and as far north as Finland, according to a fact sheet prepared by Viktoras Didžiulis, Coastal Research and Planning Institute, Klaipeda University, Lithuania. It is believed the species was transported out of its native China via lilies in the 1880s. There are three species of freshwater jellyfish, but only C. sowerbyi has become established around the world in every continent except Antarctica.
The fact sheet advises that blooms of the species are common in late summer when lake temperatures are optimum. The species prefers still water to moving water. The jellyfish spend most of their lives as 'polyps,' and it is thought they are easily transported by wildlife in this stage, along with the movement of aquatic plants.
Blooms of freshwater jellyfish have been reported in Walden Pond, where a swimmer reported finding herself in the midst of approximately "thousands" of the creatures said WBUR.
A report from the Nashua Telegraph says the jellyfish have also bloomed in New Hampshire's Naticook Lake. Once again, the report was attributed to a swimmer who found himself swimming over top of hundreds or thousands of the animals. That swimmer, Mike Malzone, told the Nashua Telegraph “It was like seeing Bigfoot or something. I’ve been fishing my whole life, and I go there at least six or seven times a year, but I’ve never seen anything like it.” Sightings of the jellyfish in New Hampshire are normally rare, said the newspaper.
The Daily Globe reported at the end of August that the species had also been found in some Minnesota lakes, reporting the species were found near the Ontario border. The last time there was a noticeable freshwater jellyfish bloom in the area was 2006.
Sightings have also been reported in Tennessee, said the Chatanoogan. An expert interviewed by the Chatanoogan said the species is common in North America, but sightings are rare as the jellyfish only blooms in the right conditions for a brief time.
Another sighting came from Brockville Ontario last week, where swimmers say they saw the jellyfish in the St. Lawrence River, according to the Reporter & Times.
Typically, when swimmers tell others of seeing hundreds and thousands of jellyfish in a freshwater lake, the response is skepticism. This prompts the people who saw the creature to return to where they saw the animal and capture a specimen. That's what Brockville Resident, 17 year old Philip Nevay did, said the Reporter & Times. Philip's mother, Francine told the paper "He's been showing it around the neighbourhood. People really want to see it."
Like most jellyfish, the C. sowerbyi has a toxin which it imparts through stinging, but the small size of the species means that the toxins do not bother most people.
Global warming, which means spring has an earlier onset and summers last a little longer, are thought to be the contributing factor to this year's sightings of the jellyfish.