Jellyfish sightings in Michigan waters? Yes, it’s a thing

1st spotted in Michigan in 1933

Freshwater Jellyfish (Myriah Richerson - USGS)

It’s not common, but there have been sightings of freshwater jellyfish throughout Michigan waters for decades.

Craspedacusta Sowerbyi, also known as freshwater jellyfish, was first reported in the United States in 1880. There have been recordings of the species in 44 out of 50 states, according to the Great Lakes Aquatic Nonindigenous Species Information System.

When it comes to the Great Lakes, the freshwater jellyfish was first discovered near Ann Arbor in the Huron River. The discovery was noted in 1933, and officials say since the 1933 recording, there have been dozens of findings of the jellyfish in our steams and inland lakes.

While jellyfish are known to be these big and scary species from the ocean, freshwater jellyfish are very different. Officials have noted that there is little-to-no evidence that these freshwater jellyfish have any significant impact on the Great Lakes.

These species have been spreading nationwide for more than a century since they were found in 1880. They travel across temperate climates, and there is little research on controlling these species due to infrequent reporting and their size.

Females (medusas) are known to be temperature-dependent, but medusae (males) are more resistant to varying temperatures. These jellyfish are no bigger than a penny.

According to the Michigan Lakes and Streams Association, freshwater jellyfish typically appear in northern temperate inland lakes during the late summer.

Making occasional surprise appearances to the delight of swimmers in Michigan’s inland lakes for well over eighty years, freshwater jellyfish are an exotic, though non-invasive species that were accidentally imported from China in the early part of the twentieth century.

Michigan Lakes and Streams Association

The U.S. Geological Survey reported that the first found freshwater jellyfish sighting in Michigan was in 1933. The last report was in 2021. A total of 25 freshwater jellyfish have been spotted in Michigan since the 20th century.

Here are a couple of locations where this species was found:

  • Lake St. Clair in 1999
  • Lake Huron in 2003
  • Flint in 1999, 2002, 2003, and 2005

----> Read: Eastern Michigan University debuts course on jellyfish research

How do these jellyfish populate in Michigan’s fresh water?

There are four ways that these species of jellyfish can reproduce, according to Central Michigan University.

There are three asexual ways that these freshwater jellyfish can reproduce:

  1. Forming a colony by budding one of more new polyps.
  2. Budding larvae produced asexually, also known as frustule, are released from the male and will then attaches themselves to another polyp.
  3. The budding larvae will grow on the side of the polyp and will release themselves as a sexually immature medusa (female).

Below is the sexual way these freshwater jellyfish can reproduce:

Props release their sperm into the water, and medusas release their eggs. The sperm and eggs will meet and develop into planula larvae that settle to the bottom of a lake or pond. Sexual reproduction of these jellyfish is rare because populations tend to be all male or all female.

Craspedacusta sowerbyi aka freshwater jellyfish (Myriah Richerson - USGS)

So are freshwater jellyfish a threat to the Great Lakes?

The impacts of the freshwater jellyfish populations are unclear to many studying the species. According to the Great Lakes Aquatic Nonindigenous Species Information System, male freshwater jellyfish were killed and fed on striped bass larvae under laboratory conditions in 1978.

A European study found that there was a significant decrease in small crustaceans and an increase in chlorophyll concentration, suggesting freshwater jellyfish can have an impact on the zooplankton community.

These jellyfish can sting and paralyze macroinvertebrates and small fish, but there is no dangerous threat to humans.

The main predator of these species is crayfish.

“Freshwater jellyfish are an invasive species that are now found on every continent except Antarctica, but their appearances each year are somewhat unpredictable, making it difficult to collect data,” said a graduate student in the biology program at Eastern Michigan University Rachel Koski. “In comparison to other species of jellyfish, there is a lack of literature on freshwater jellies, so being able to research them and gain more knowledge about their ecology and distribution is awesome.”

Below is a map of where freshwater jellyfish has been spotted in Michigan since 1933:

Click here to view a table of all the national findings on freshwater jellyfish.