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Freshwater Jellyfish Found in Namakan Lake

Freshwater jellyfish—Craspedacusta sowerbii — were found in Namakan Lake over the weekend by a fisheries specialist for the Minnesota DNR.

Usually about dime to quarter size in diameter, freshwater jellyfish are white to opaque in color and spend most of their lives living as polyps near the bottom of freshwater lakes and wetlands. It is only occasionally that the jellyfish mature from their polyp form into the recognizable, dome-like jellyfish shape of their salt-water relatives and move into surface waters. Researcher believe this change in morphology is intimately linked to increasing water temperature.

Warmer water allows for the development of surplus zooplankton, meaning a surplus of jellyfish food, and thus a larger population of resident jellyfish in Minnesota lakes. Additionally, researchers believe that the warming trend of earlier ice-outs and prolonged lake warmth into the fall, means that warmer temperatures are reaching further down into lakes—allowing more jellyfish polyps to develop into their mature form. As larger numbers of polyps mature, more and more make their way to the surface, creating what has been deemed jellyfish “blooms.” Each bloom lasts only a few days, and occur usually at the end of the summer during peak water temperature.

Sightings of freshwater jellyfish this summer have also been recorded in the Boundary Waters Canoe Area Wilderness and in Winona County. Researchers believe that as the warming pattern continues in Minnesota lakes, the frequency of jellyfish blooms will increase as well.

For more information, and to the view an original article from the Duluth News Tribune, visit http://www.duluthnewstribune.com/event/article/id/177547/publisher_ID/36/