These invasive jellyfish are the size of a thumbnail — and they're making a new home in B.C.

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The next time you dip your toes into a lake in British Columbia, you might want to take a closer look at the water.

That's because an invasive species of jellyfish believed to be native to southeast China, Craspedacusta sowerbii, is making a new home for itself in B.C.'s freshwaters.

"We know they are there. We know they are potentially widespread. But before we go a step further, we need to know what they do and then we can talk about that," said Florian Lüskow, a University of British Columbia PhD candidate and researcher.

Lüskow, who studies gelatinous sewer plankton, was first informed of the presence of jellyfish in some of B.C.'s freshwater lakes in 2020. He said the discovery was surprising.

"In a very peaceful environment, such as a small lake, you would never expect to find a jellyfish," he said. 

Lüskow spoke to The Current guest host Nahlah Ayed about the jellyfishes' presence in B.C.'s freshwater areas, how they compare to their ocean relatives, and the role of climate change in their arrival. Here's a part of their conversation.

Could you tell me about this jellyfish? What are they?

I guess we all know jellyfish from the ocean, and similar to those, they are just transparent, gelatinous soft-bodied creatures, invertebrates, literally, that are swimming and drifting in the water column.

In contrast to their ocean brothers and sisters, they are relatively small — never grow much bigger than the size of a thumbnail.

But otherwise, they represent ocean jellyfish pretty much. They have plentiful tentacles, they have an umbrella and they do the typical pulsation movement.

You make them sound really kind of innocuous, but tell me more about those tentacles. There's a lot of them.

Jellyfish, as we know them from the ocean, have a few dozen of them, maybe a little bit over a hundred. But these jellyfish have literally several hundred, maybe close to a thousand. 

The reason for that is still a little bit in that debate. It's a matter of prey capture — and obviously, these tentacles are the instrument for this prey capture. 

They are spiked with nematocysts … a certain cell which contains a harpoon. [At the] moment of a prey contact, this harpoon is pulled towards the prey and basically injects the skin and the toxin with it. This toxin eventually leads to paralysis of the prey and eventually to its death.

But we're talking about fairly, fairly small prey here because it isn't a very big organism.

You're absolutely right. So the jellyfish itself is never bigger than, let's say, the size of a coin, maybe a thumbnail. So its prey is usually tiny. We're talking about plankton organisms.

So where do they come from? How did they get here?

The general belief is that they are coming from southeast China … a subtropical area. So the species appreciates the higher temperatures. So that's why we usually see it in the second half of the year. 

The question of how they actually arrived here…. There are so many hypotheses around this, but we have no definite answers.

At the moment, we have the feeling that they are … transported with water birds or with boats. Basically being attached to the feet of the birds or attached to the hulls of the boat and then transported from one lake to another. 

But this is barely possible over a distance of several thousand kilometres. So there's questions around this, that's for sure.

So we don't know exactly how they got here. But tell me about the time that you first encountered these jellyfish.

I was called by an observer on Vancouver Island who used to swim in a lake year after year. And she basically said … there's something that reminds her [of] a jellyfish. But everybody knows that there [are] no jellyfish in a lake. 

So she [worried] a little bit and reached out to me because she knew that I'm working with gelatinous sewer plankton in the ocean. So I basically went over to Vancouver Island and inspected that lake and actually confirmed her observation that it's a jellyfish. 

[These] are, by chance, the areas where you have in the summer the most temperatures, so it's never getting extremely warm. Also in the winter, it's getting never extremely cold.-Florian Lüskow, UBC researcher.

So where are you finding them now? How widespread are they?

So at the moment, we see them in many lakes in southern British Columbia and also on Vancouver Island. 

[These] are, by chance, the areas where you have, in the summer, the mild temperatures, so it's never getting extremely warm. Also in the winter, it's getting never extremely cold. 

But it's also the areas where you have the highest population density…. Our observations are very much biased towards these population centres; Vancouver, Victoria, Nanaimo, just to name a few. 

It's very likely that there's also jellyfish further in the interior and further to the north. It's just a matter of observing them and eventually reporting them back to us. 

So I'm curious, is the trend up? Are the numbers higher as time goes on?

Unfortunately, we don't have a long-term record of this. The government hasn't included it in any monitoring systems on a broader scale. So at the moment, I don't dare to say anything about long-term trends.

But looking at the global picture, we believe there will be increasingly good conditions for the species. So it is also likely that it's getting more prominent in British Columbia and elsewhere in Canada.

I guess what you might be hinting at there is a role for climate change in all of this. What role does climate change play in the numbers here?

The jellyfish only occurs at the end of the summer into early fall, and then dies off later on when the temperatures go down again. But there's another part of the lifecycle called the polyp. 

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These polyps are sitting along the sea floor, the lake floor, long branches, submerged stones, stuff like that, and basically around all year. 

Once the temperature becomes feasible for the production of jellyfish, they just invest energy and start producing those jellyfish. This is certainly triggered by a higher temperature. Usually, it's something like above 20 degrees. 

So if we follow the current predictions about climate change and water warming in our area, we might expect that the lakes [are] becoming warmer earlier in the year and also stay warmer for a longer period within the year.

Written by Mouhamad Rachini. Produced by Niza Lyapa Nondo. Q&A has been edited for length and clarity.