Freshwater jellyfish could be spotted in Michigan lakes, streams
MICHIGAN (WNEM) - Anglers, swimmers, and other water recreation fans may catch a glimpse of the common, but rarely seen, freshwater jellyfish in Michigan lakes and streams.
Freshwater jellyfish (Craspedacusta sowerbyi) are not a true jellyfish, since they have a membrane called velum that true jellyfish do not have, the Michigan Department of Natural Resources (DNR) said, adding despite the difference, the appearance and movement of freshwater jellyfish mimic those of a true jellyfish.
According to the DNR, they are not native to Michigan or North America and are believed to be native to China and Asia, however freshwater jellyfish have been found throughout most of North America for over a century. They are considered to be a nonharmful member of Michigan’s aquatic community.
In 1933, freshwater jellyfish were first documented in the Huron River in southeast Michigan, the DNR said, adding they can now be found in most Michigan lakes and streams.
They are more frequently spotted in lakes in the late summer and early fall.
“These are the sightings that often trigger calls to local DNR offices from curious spotters who have caught the rare glimpse of the invertebrate,” said Tim Cwalinski, the DNR’s northern Lake Huron manager.
Cwalinski said while they do have stinging cells, freshwater jellyfish cannot sting due to their tiny size and are not harmful to humans. He also said it’s unlikely they could consume enough zooplankton to negatively compete with fish.
Freshwater jellyfish are polymorphic, which means there are multiple forms of the same entity within a population, according to the DNR.
The DNR said the jellyfish life cycle follows these steps:
- Jellyfish spend winter in bodies of water in a podocyst resting stage.
- As conditions become more favorable, like during spring, the podocysts develop into polyps and continue the life cycle with asexual reproduction.
- By late summer polyps develop into the medusa stage, which most resembles a free-swimming jellyfish.
- Jellyfish in this stage take an umbrella-shaped form and can range in size from a penny to a quarter.
- This life stage is visible to the human eye.
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