A local resident reported an unusual sight at Spencer Lake in Waupaca County last week – freshwater jellyfish (Craspedacusta sowerbyi). Paul Skawinski, Regional Aquatic Invasive Species Education Specialist for Golden Sands Resource Conservation & Development Council, Inc. in Stevens Point visited the lake and confirmed the report. These strange creatures originate from China, and were first observed in Wisconsin in the late 1960s. They are thought to have arrived by clinging to aquatic plants that were imported for water gardens or aquarium use, and later escaped to the wild during flooding events or through illegal dumping of aquarium water or plants. A total of 94 Wisconsin water bodies are currently known to contain freshwater jellyfish. Impacts of the freshwater jellyfish on Wisconsin’s ecosystems are not well known. They feed on zooplankton, the same food source of young fish, so they may have some impact to fish populations. According to Skawinski, these jellyfish do contain stinging cells on their tentacles, but these cells are harmless to humans. “Their stinging cells are only effective against small creatures like plankton. They are too small to pierce human skin, so they pose no threat to swimmers or other lake users”, he said. The mature life stage, known as the medusa stage, is the familiar one with a bell-shaped body and long tentacles. A fully-grown individual is only about one inch in diameter, and is mostly transparent, making them very difficult to see in the lake. This stage is short-lived, and jellyfish are unlikely to be observed in any other life stage. Anyone that observes freshwater jellyfish or another aquatic invasive species is encouraged to contact Golden Sands RC&D Council at 715-343-6215, or info@goldensandsrcd.org. More information about the Golden Sands regional aquatic invasive species program can be found at www.goldensandsrcd.org.
