As a lake researcher, I have encountered many people in recent years who ask me whether jellyfish really live in lakes. Some people think they’ve seen something, or that their friends or family have seen it. I’ve even heard of marital fights over this issue! So, are there jellyfish in Canadian freshwater lakes or not?

Yes, there are jellyfish in lakes in Canada. These organisms are related to saltwater jellyfish (Cnidaria) but are much smaller. The reason why more people are suddenly aware of these creatures is because their numbers are increasing; Their numbers are increasing due to climate change.

The bottom line is that freshwater jellyfish are real, and Canadians need to get used to their increasing presence in our lakes as the planet warms.

This article is part of our series Our lakes: secrets and challenges. speech and La Speech We invite you to a fascinating dive in our lakes. With magnifying glasses, microscopes and diving goggles, our scientists examine the biodiversity of our lakes and the processes taking place in them and tell us about the challenges they face. Don’t miss our articles about these incredibly rich bodies of water!

Craspedacusta is on the rise

Currently the most commonly observed breed in many parts of the world, including Canada Craspedacustawith most common types Craspedacusta sowerbii. Some have given it the common name Peach Blossom Jellyfish. In French it is simply known as “”.méduse d’eau douce”.

This species of freshwater jellyfish was first described and scientifically named in 1880 at the Royal Botanic Gardens in London. They are an introduced species outside their native China and It has been observed on all continents except Antarctica.

These jellyfish cannot sting humans; so you don’t have to worry about encountering them while swimming. Their diameter is between one and two and a half centimeters and they are mostly transparent. When their “bloom” occurs they can be very abundant and appear in the hundreds to thousands. However, these blooms usually only last about a week or two; This lasts long enough for them to achieve sexual reproduction.

Freshwater jellyfish have long been found around some lakes in southern Canada. The earliest detection that we know of was in Lake Québec in 1938.. So why are we hearing more about them now? There are several main reasons.

invisible being

Peach Blossom Jellyfish spends most of its life life cycle as a small polyp about one to two millimeters long. A population of polyps can survive for years by reproducing by budding in this asexual stage.

In this form, they live attached to vegetation, rocks and other surfaces near the lake bottom and are difficult to see. They feed on other passing organisms; mostly small crustaceans called zooplankton and especially those living near lake edges. During periods when the environment is colder and food is less available, they enter a dormant phase called podocyst.

But sightings of the larger, bell-shaped gelatinous forms typical of the jellyfish we all know (and try to avoid when swimming) are increasingly being reported. What is the connection?

The mature form of the Peach Blossom Jellyfish is only produced under the right environmental conditions. A critical trigger appears to be warm temperatures. When are the water temperatures exceed 25 CFully grown jellyfish may suddenly appear in large quantities.

This species has been living there as a polyp, perhaps for years, and suddenly ghost-like jellyfish appear as if out of nowhere and bloom profusely in the lake.

invisible invader

The first observation of the most common freshwater jellyfish is thought to have originated from imported Chinese plants at the Royal Botanic Gardens; Plants to which polyps or their dormant forms can easily be attached. This is a typical way aquatic invasive species Move around the planet.

The movement and migration of waterfowl may also play a role in how these occur. moved across lakes or continents. More locally, they may be distributed by recreational lake users. not cleaning their equipment adequately between bodies of water. Natural processes are also at work, with polyps and durable podocysts being transported by animals and water flowing from one lake to another. Over time, as more lakes are colonized, more reports of jellyfish sightings will emerge.

As noted, warm water temperatures appear to be the main trigger for the mature form of freshwater jellyfish. The original habitat of these organisms is tropical-subtropical Asia. So, as climate change increasingly warms the waters of northern temperate lakes, we will see more blooms of Peach Blossom Jellyfish. Climate change is pushing the habitable zones for these creatures further north. Recent modeling has shown.

Results

What will happen to lake food webs as jellyfish emerge more frequently in their mature form, feeding on plankton in the water column and not just at lake margins? This is still largely unknown. We still have a lot to learn about these organisms and their effects because they are difficult to study. It is difficult to culture in the laboratory, and we cannot yet predict when it will bloom in nature.

Some laboratory studies have shown that the mature form can consume 16 times more plankton prey than polyps.. Given that blooms are generally short and zooplankton reproduction rates are relatively high when waters are warm, it is still an open question whether this leads to a significant loss of zooplankton in the lake.

Zooplankton is an important prey for some fish species, especially juvenile fish. But for now, the emergence of waters warm enough to produce mature jellyfish (usually in mid to late summer) does not coincide with the emergence of young fish (usually in early summer). It is not yet known whether the timing of species interactions will overlap more as the climate warms, as species will likely adapt at different rates.

As the waters of northern temperate lakes stay warmer for longer, we run the risk of freshwater jellyfish becoming more permanent members of the summer food web. This may reduce prey availability for fish species such as: cisco (Coregonus spp.)They rely on zooplankton prey as their main meal.

Therefore, with climate change, not only are reports of human sightings expected to increase, but also the impact of these freshwater jellyfish on lake food webs is expected to increase.

Beatrix Beisner receives funding from NSERC and FRQNT. He is Co-Director of the Groupe de recherche interuniversitaire en limnologie (GRIL), a research network of 12 Québec universities.