A mucilaginous mystery: Freshwater jellyfish in Minnesota lakes

[Carl Karasti]

FYI — Something new to be aware of in our waters.

I just came across this, which I hadn't heard of before now, from Jan 31.  The text and the image is here, along with a link to the source.

The webinar mentioned at the end already happened on Feb. 6.

Carl Karasti

A mucilaginous mystery: Freshwater jellyfish in Minnesota lakes
By Charlie Mitchell
Published January 31, 2025 at 3:58 PM CST

Freshwater jellyfish are invading MN lakes! Professor Beatrix Beisner discusses their arrival to the area, hidden life cycle, and how to prevent their spread.

Have you spotted an eerie aggregation of tiny white jellyfish in Minnesota lakes? You’re not hallucinating—they’re real. Beatrix Beisner, a professor of biology at the University of Quebec in Montreal, joined the KAXE Morning Show to discuss the science behind these unexpected blooms of freshwater jellyfish.

The peach blossom jellyfish, an invasive party crasher originating in subtropical China, seem to mimic the habits of human tourists to Minnesota. They disappear during the bitter winters, only to show up to lakes in large numbers during the long, sun-soaked days of summer.

Unlike human tourists, these jellies aren’t interested in a brisk swim on a hot day – they only show up when water temperatures exceed 77 degrees. On the rare occasion they are visible, they appear in huge groups. These aggregations, called “blooms,” happen when water conditions are suited for the adult jellies (called medusas) to mate. After about a week, the medusas finish releasing their eggs and die off.

(As Beisner points out, you need not fear swimming with the jellies. Their tentacles and stinging parts are not large enough to puncture human skin; they feed on tiny zooplankton. Their ecological impact seems minimal for now, but climate change might make their sudden summer blooms into more than just an oddball spectacle.)

Despite the showy aggregations of adult medusas, jellyfish spend most of their life in stealth mode. Their young take the form of tiny, one-sixteenth of an inch polyps which anchor themselves to rocks and plants. There they wait, filter-feeding and waiting for the right time for a tentacular transformation.

Once a lake has been invaded, years may go by without visible blooms. On the lake bottom, the tiny, microscopic polyps remain in their larval form, waiting for favorable conditions.

To stop the spread of these jellyfish, Beisner suggests the same tried-and-true method that has worked for other aquatic invasives: Clean your boats, boots, and gear! Jellyfish eggs are resilient stowaways that cling to plant, rock, and other surfaces. They are able to withstand long periods of drying, freezing, and heat. By removing the surfaces they cling to, you can vastly reduce or eliminate the movement of these invasive interlopers.

Curious to learn more? Professor Beisner is presenting the February edition of the “Practical Water Wisdom” series, hosted by Itasca Waters. The webinar is at noon on Feb. 6, and participants can register at the Itasca Waters website.

https://www.kaxe.org/show/91-7-kaxe-90-5-kbxe-morning-show/2025-01-31/a-mucilaginous-mystery-freshwater-jellyfish-in-minnesota-lakes

Freshwater jellyfish in their adult hydromedusa form float in water.

[Juile Grahn]

I watched the Itasca Waters webinar on Feb 6th.  It was very very interesting!  Itasca Waters archives their webinars so one can go to itascawaters.org to watch it.  Look for Practical Water Wisdom 2025 Series # 1. I have watched several of their webinars and they have all been good.  

Julie Grahn

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