The freshwater jellyfish, or Craspedacusta sowerbii from its Latin name, is well established in several lakes in Quebec and risks taking advantage of climate change to proliferate. Even if it is harmless to humans, it is quite a surprise for unsuspecting swimmers.
“We expect to see more and more of them because of the temperature of the lakes that are increasing,” explains Beatrix Beisner, professor in the Department of Biological Sciences at the Université du Québec à Montréal. The creature, originally from China, was first recorded in Quebec in 1930, at Horseshoe Lake in Sainte-Agathe-des-Monts, according to the researcher.
Although it has been present in Quebec’s waterways for almost 100 years, the freshwater jellyfish has long gone unnoticed. Research by Béatrix Beisner and her colleague Nadia El Moussaoui shows that when the temperature of a lake is below 25 °C, it takes the form of very small polyps that are impossible to see with the naked eye.
Attached to rocks or plants at the bottom of a lake, the polyps can remain there for decades. Then, when the water temperature rises above 25°C, they transform into jellyfish. “They prefer warm water, the rising temperature favors them,” says the biologist. It is in the jellyfish state that the creature reproduces and becomes increasingly visible. “They are too small to burn us,” adds M.me Beisner.
No danger for now
Dominic Loiselle is a biologist and diver for his company, Subaquatique. He is fascinated by these creatures, which he is constantly looking to photograph in new waterways. “Usually, it’s late August, early September that I start seeing them.”
Because of the occasional nature of the hatches, “you have to be lucky to see them,” he explains. “It’s a really special animal, but most people don’t even know it exists in Quebec. However, this jellyfish is colonizing the entire planet.” Several sightings have been recorded in the eastern United States, Europe and Asia. In a 2021 podcast, the City of Paris even confirmed the presence of these jellyfish in the Seine, where athletes will swim at the 2024 Olympic Games.
Individually, jellyfish are harmless. It is rather their invasive nature that is of concern. Freshwater jellyfish are considered to be predators of zooplankton, an important food source for fish and an important element for the well-being of the ecosystem. If jellyfish colonies were to develop in too great a number, the quantity of zooplankton could fall, thereby jeopardizing the balance of the ecosystem. The Quebec Ministry of the Environment is monitoring the situation and potential dangers.
For the moment, “the impacts are rather minimal, since the outbreaks are quite occasional,” says researcher Béatrix Beisner.
An invasive species, but monitored
Last week, the Estrie Regional Environmental Council (CRE) added freshwater jellyfish as an invasive species to its list of contaminated bodies of water in the region. To date, 7 of the 151 bodies of water identified in Estrie are thought to be affected by the presence of these jellyfish.
Elsewhere in Quebec, their presence is not necessarily listed by body of water, but the Ministry of the Environment estimates that the species is established in the following regions: Capitale-Nationale, Chaudière-Appalaches, Lanaudière, Laurentides, Mauricie, Centre-du-Québec, Montreal, Laval, Montérégie, Outaouais and Saguenay–Lac-Saint-Jean.
Julie Reinling, communications officer for the Missisquoi Basin Watershed Organization (OBVBM), believes that the best way to combat these infestations “is to prevent them.” “Just like you brush your teeth in the morning and evening, when you visit a body of water with a boat, or even to swim, you have to clean everything that has been in contact with the water.” This way, invasive species cannot accidentally end up in other bodies of water. “We limit the damage,” she said.