Freshwater Jellyfish Appear in Namakan Lake

Tiny freshwater jellyfish have recently made a rare appearance in Namakan Lake along the Ontario border.  The creature — Craspedacusta sowerbii — is the size of a small coin and typical shows itself toward the end of warm summers.

Freshwater Jellyfish (Craspedacusta sowerbii) photo courtesy http://www.freshwaterjellyfish.org/picture11.html
Freshwater Jellyfish (Craspedacusta sowerbii) photo courtesy http://www.freshwaterjellyfish.org/picture11.html

The Duluth News-Tribune has a story on the recent discovery HERE.

The jellyfish is a regular resident of many Minnesota lakes, but it is not often seen in its signature hydromedusa state.  The hydrozoa spends more of its time as a polyp, attached to the bottoms of lakes.  However, in warm summers that are rich in zooplankton, the jellyfish’s food source, the species often morphs into its gelatinous, tentacled form.

Freshwater jellyfish are thought to be an exotic species to North America, although their decades-long presence in Minnesota lakes has not posed an ecological problem, according to experts.  It is thought that longer ice-free periods for Minnesota lakes and warmer summers may make jellyfish blooms more frequent.

While freshwater jellyfish immobilize their prey with their stinging tentacles, they do not pose a threat to humans.

The U.S. Geological Survey has a fact sheet on freshwater jellyfish HERE.

We also recommend the essay in THIS issue of Wilderness News about contributor Andy Wright’s freshwater jellyfish encounter on the BWCAW’s Ruby Lake.

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