A freshwater relative of the larger ocean creature is the latest ‘invasive’ species to enter Lake Erie

Associated Press

ERIE, Pa. — They’ve been in the Great Lakes Basin for decades, but have recently entered lakes Erie and St. Clair.

Freshwater jellyfish — about the size of a penny or quarter — are translucent, slimy blobs that inhabit lakes, streams, ponds and some rivers in Pennsylvania and much of the northeasternUnited States.

Like their saltwater counterparts, freshwater jellyfish will sting people, but their stingers are so small they would not penetrate human skin.

Some biologists categorize freshwater jellyfish as an invasive species, while others, like Sara Stahlman, an invasive species specialist with Pennsylvania Sea Grant, place them in the “non-native species”realm.

Whatever their classification, the invertebrates have been floating around portions of the Great Lakes ecosystem for decades. The Ontario Ministry of Natural Resources and Forestry reported that freshwater jellyfish appear to have entered Lake Erie and Lake St. Clair, a small lake between lakes Huronand Erie.

“They’ve been around for quite some time in Pennsylvania, since the early 1990s,” Stahlman said. “They prefer more slowly moving, stagnantwaters. They’re found in ponds, lakes and slower movingrivers in Pennsylvania.”

Off Erie County shores Craspedacusta sowerbyi falls under the management of the state Fish and Boat Commission, but little mention of the animal appears on the agency’s website. It has no Pennsylvania conservation classification. The jellyfish eat zooplankton and use their stingers to catch prey. At its current population level it does not challenge other zooplankton-eating species for food resources in Lake Erie. Turtles and crayfish eat the jellyfish.

The species exists in two forms: a polyp and a hydromedusa,or adult form.

“In the polyp form, they would not be as recognizable to people,” Stahlman said. “They can be dormant in sediment for a long time. They seem to be concentrated more in the eastern part of the U.S. In Pennsylvania, they’re all over the place. It’s a temperature-dependent type of situation. You see more of the adult forms in warmer-temperature waters.”

More than 180 aquatic invasive and non-native species have become established in the Great Lakes Basin, according to the 2017 State of the Great Lakes Highlights Report, a study conducted by the U.S. Environmental Protection Agency and Environment and Climate Change Canada.

Some of the more wellknown invasive species that inhabit the Great Lakes Basin include zebra and quagga mussels, round goby, rusty crayfish, sea lamprey and the predatory northern snakehead fish.

Most researchers and authorities do not believe freshwater jellyfish pose any threat to humans or the Great Lakes ecosystem.

“I would categorize these jellyfish as a non-native species and not necessarily as an invasive species,” Stahlman said. “Invasive species are very harmful from a health standpoint to humans, from an ecological standpoint and from an economic standpoint. It’s still to be determined how the jellyfish are impacting the ecosystem, but they do not really seem to be impacting the