(WWJ) - If you spot what appears to be jelly fish while swimming or fishing in lakes or rivers in Michigan this time of year, don't be alarmed -- they've been here for almost a century.
According to the Michigan Department of Natural Resources (DNR), sightings of a common, but rarely seen invertebrate "Craspedacusta sowerbyi" -- also known as freshwater jellyfish -- prompts a flurry of calls in late summer and early fall, but officials said if you happen to see these creatures, "consider yourself fortunate."
Tim Cwalinski, the DNR's northern Lake Huron manager, said that the aquatic animal is believed to have originated in China and Asia, but has been found all throughout waterways in North America for over a century. They were first documented in Michigan in 1933 with sightings in the Huron River in southeast Michigan.
DNR officials state that the tiny invertebrate aren't necessarily "true" jellyfish since they have a membrane called a velum that the marine species lacks, but they move and look just like their cousins -- which often surprises Michiganders if they get the chance to see them.
"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 Cwalinski. "Though freshwater jellyfish do have stinging cells like the marine species, their tiny size means they lack the ability to sting, and so they're not harmful to people. It is also believed to be unlikely that freshwater jellyfish could consume enough zooplankton in our bodies of water to negatively compete with fish species."
The creatures can be found in most Michigan lakes and streams and are commonly seen in lakes around this time of year.
According to the DNR, freshwater jellyfish are polymorphic, meaning that there are multiple forms of the same entity within a population.
The jellyfish life cycle includes the following steps:
• The jellyfish spend winter in bodies of water in a podocyst resting stage.
• As conditions become more favorable, such as 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 is the life stage that is visible to the human eye and often observed during late summer.
While Michiganders often think only fish, birds and aquatic plants occupy our waters, Cwalinski said there is a whole plethora of life forms that call Michigan home, such as plankton, bryozoans and jellyfish.
"If you're among those to observe a single medusa stage or colony of freshwater jellyfish this year in our lakes or slow-moving streams, consider yourself fortunate, don't panic, and understand this is simply an invertebrate that has inhabited most of our waterways for a century."