URBANA-How could something just one centimeter in size, cause enormous problems for Lake Michigan? Easy, when you’re a water flea with no known enemies in the area. Cercopagis pengoi, (sometimes called the fishhook flea), has recently invaded the waters of southern Lake Michigan, and is tiny but prolific. It reproduces rapidly, has no known predators, and can create havoc by upsetting the lower levels of the food chain. Patrice Charlebois, biological resources specialist for Illinois-Indiana Sea Grant noted that although this water flea was found earlier this year in Grand Traverse Bay, it is now posing a threat closer to home.

It was first spotted in the open waters of southern Lake Michigan by Burt Atkinson, captain of a charter boat named "Donna G", who was out with a party off Waukegan Harbor. The captain noticed the masses (which can look and feel like wet cotton batten) on his lines and knew they were different from the other spiny water flea, Bythotrephes cederstroemi. Charlebois, checked zooplankton samples collected in the same area but closer to shore by her home institution, the Illinois Natural History Survey’s Lake Michigan Biological Station. She found them to be not only present in the sample, but fairly abundant.

Charlebois has followed the invasion of the spiny water flea and worries that this new species could cause even greater problems for the Lake Michigan ecosystem. As is the case with its predecessor, this new invader feeds on tiny aquatic organisms called zooplankton, which are an important food source particularly for young fish. So, Cercopagis could compete for the same food as these fish. Cercopagis also has little barbs on its tail, which gave it the nickname, "fishhook." The barbs make it difficult for small fish to eat them, and without a predator, the fishhook flea can concentrate on multiplying.

"We’re concerned about the potential impacts that Cercopagis will have on the Lake Michigan foodweb. The fact that Cercopagis feeds on other zooplankton and is not easily consumed by fish could have detrimental impacts on all levels of the lake foodweb. The foodweb has already been compromised by other exotics such as the spiny water flea and the zebra mussel." Charlebois goes on to say that Cercopagis could also be a serious threat to yellow perch. Young yellow perch rely on zooplankton as a food resource. "If Cercopagis strikes another blow to this already battered resource, yellow perch may feel the impact again."

So, what can be done to stop or slow down the spread of this potentially destructive water flea in Lake Michigan and inland lakes? Boaters and anglers can help prevent the spread of Cercopagis by observing many of the same procedures used to prevent the spread of other exotic species. Taking the time to do simple things like inspecting the boat and removing plants and animals from equipment; draining the boat of all lake or river water (including the bait bucket); dumping bait on land or in the trash, never in the water; and rinsing the boat with a high-pressure sprayer or 104ºF degree water or allowing the boat to dry for at least five days before transporting it to another body of water can greatly slow and even stop the spread of Cercopagis and other exotic species.

If you would like more information on the newest exotic species invader to southern Lake Michigan, contact Patrice Charlebois, (847)872-0140

Irene Miles
Illinois-Indiana Sea Grant
376 NSRC
1101 W. Peabody Dr.
Urbana, Il 61801
Phone:  217-333-8055
Fax:  217-333-8046
miles@illinois.edu