Alien-looking blob discovered in southern Michigan lake

Suspicious aquatic oddity attached to boat is actually indicator of good water quality

This alien-looking blob was found attached to a pontoon boat.
This alien-looking blob was found attached to a pontoon boat. Photo by C. Daly.

As an aquatic ecologist at Michigan State University who works closely with Michigan State University Extension, I receive a lot of emails and phone calls about mysterious or unusual discoveries in Michigan lakes. I enjoy responding to them, because it gives me a chance to chat with Michigan residents about all sorts of interesting aquatic phenomena.

This story begins with one of those messages. A boat owner pulled their pontoon out of Juno Lake (Cass County, in southern Michigan), and discovered a weird, alien-looking, gelatinous blob attached to it below the water line. Was it an invasive species? Toxic algae? Eggs of an alien from outer space!? They contacted a friend on a neighboring lake who happens to be a volunteer in our statewide Cooperative Lakes Monitoring Program, and she reached out to me with a photo and inquiry about the aquatic oddity. I was excited to let her know that they’d discovered a colony of bryozoans!

Meet the bryozoans – tiny aquatic organisms that live in colonies. They are filter-feeders, relying on floating bits of food in the water for nourishment. You can view the waving tentacles of a microscopic bryozoan individual on this video. There are many saltwater species of bryozoans, but only a few are native to freshwater lakes. The freshwater bryozoan species that makes blob-like colonies is Pectinatella magnifica. These colonies often form attached to structures like rocks, logs, and – as was the case in Juno Lake – on boats left in the water for a while. Colonies begin to form in the spring, and are most frequently noticed in late summer and fall, when they reach their largest size. Colonies are usually only a few inches across, but can grow to a foot wide or more in the right conditions.

Bryozoans on pontoon_LMroczek

Bryozoan colonies attached to the underside of a pontoon boat pulled from Juno Lake, Cass County, Michigan. Bryozoans are harmless, tiny, filter-feeding aquatic invertebrates that can form jelly-like colonies on solid surfaces. Photo by L. Mroczek. 

Still, most Michigan residents have never seen a bryozoan colony before, since they are underwater and often small in size. It’s not surprising, then, that these jelly-like, alien-looking blobs raise concern and worry when they are spotted. Luckily, these native species are harmless to humans (although they do occasionally clog pipes). Even better, they are indicators of good water quality, since they depend on healthy waters to survive.

To learn more about freshwater bryozoans, check out the Missouri Department of Conservation’s excellent web article. If you find an aquatic oddity in Michigan and aren’t sure what it is, take a picture or two and post it using the  Ask an Expert link on the Michigan State University Extension website.

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