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Freshwater Jellyfish-Who Knew?

September 16, 2010

Several weeks ago a family of vacationers found some jellyfish in a small, eastern Manitoba lake. The discovery was considered so rare that it made a splash in the local media. Jellyfish in a LAKE, a cold, freshwater, local lake! Who knew?!
Of course, the media played it up as another reason to be scared. Another dangerous, new, invasive species. Watch out, Manitobans! Pollution, environmental disaster, global warming. etc., etc.
It turns out that a few observant biologists here had previously seen this species of jellyfish, Craspedacusta sowerbyi, in Manitoba. Its appearance here is unusual and unpredictable but not rare. There is nothing to be concerned about.
I must confess that my only experiences with jellyfish have been confined to seeing beaches closed in Australia because of lethal salt water varieties and warnings in Florida and California about bluebottles. So, the discovery turned into quite an educational moment for me.
Craspedacusta sowerbyi are so tiny and clear that they have probably gone unnoticed by most swimmers and boaters. They’re about the size of a quarter and so weak that the sting is harmful only to small fish and plankton.
Although Craspedacusta sowerbyi originated in China, they can now be found throughout the world, including almost all of Canada and the US. (According to Wikipedia, the only states with no reports are Montana, Wyoming, North Dakota, South Dakota, Alaska or Hawaii and the provinces of Alberta or Saskatchewan.)
What’s most interesting about them is how they got here, and evidently how they escaped China. They start out as tiny polyps, go dormant in the winter, and get transported as polyps from one fresh body of water to another by aquatic plants and animals. They likely hitchhiked to Manitoba as dormant podocysts via some unwary ducks or geese and then grew into jellyfish.
Freshwater jellyfish. Now I know. Look for them in a lake near you.

3 Comments leave one →
  1. Shadla Cycholl permalink
    September 21, 2010 1:16 pm


    It was a delight to meet you last week and thank you for introducing me to the website – I will enjoy it!

  2. September 24, 2010 7:00 pm

    Thank you for unraveling the mystery behind these jellyfish. We came in contact with them while swimming in a fresh water pond located in Mendocino County, California. We couldn’t believe our eyes.

  3. Lisa Leonard permalink
    September 30, 2010 12:20 am

    We caught one up in Gravenhurst, ON last weekend and brought it home but it died after a couple of days… My daughter was so intrigued that she wants to catch a couple more but what do they eat and can you keep them alive for a while in a jar? That one didn’t make it because I didn’t know what to feed it!


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