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Don’t be surprised to discover jellyfish in Missouri freshwater bodies

Freshwater jellyfish
Jim Rathert
Missouri Department of Conservation
A freshwater jellyfish in an aquarium in 1998

A non-native species of jellyfish from the Yangtze River Basin in China is thriving in St. Louis region freshwater habitats.

The species Craspedacusta sowerbii, also known as the peach blossom or freshwater jellyfish, is common throughout Missouri’s lakes, reservoirs, and other slow-moving bodies of water, according to the Missouri Department of Conservation.

The jellyfish have been in the United States since 1888. The first one collected in Missouri was in 1930 from a quarry pit in St. Charles County, said Will Mabee, an aquatic animal researcher with the Department of Conservation.

“They've always interested me, just because they're jellyfish, and we're in the middle of the continent. People normally associate these creatures with saltwater,” Mabee said.

The Department of Conservation suspects the jellyfish could have hitchhiked on an aquatic plant display over 100 years ago as inconspicuous polyps.

They are the size of a quarter, and feed on microscopic crustaceans called zooplankton. “If you're looking for something that cues in on the jellyfish possibly being in a freshwater habitat, look if there is a good population of zooplankton,” Mabee said.

The jellyfish toggles between two life stages: a polyp form and a medusa form. During the polyp form, they are even smaller than a quarter and attach themselves to submerged plants or at the bottom of a lake.

Freshwater jellyfish side
Jim Rathert
Missouri Department of Conservation
A freshwater jellyfish in its free-swimming, medusa stage, which has an umbrella-like body with a stomach extending downward from the center.

“They are sessile in this stage. So, they don't actively swim up and down through the water column, like the medusa stage does,” Mabee said. In this stage, the polyps form buds that separate and become new individuals.

The polyps transform into a normal-looking jellyfish, umbrella-shaped with tentacles, when the waters get warmer.

“The medusa stage in the lifecycle is the actual jellyfish stage,” Mabee said. In Missouri, this stage appears in late July, and will go through early September.

Mabee said there have been reports of freshwater jellyfish in Lake Ozark, Stockton Lake, Lake Pomme de Terre, Tom Sawyer Lake and Table Rock Lake, but they are difficult to track.

“They just pop up, you know. They just are there and then they're gone,” he said. “They reproduce asexually by budding. So, it would be very difficult to get a population estimate.” Even though the jellyfish are non-native, they are a well-established part of Missouri fauna now.

The tiny stingers on the jellyfish's tentacles do not affect people. They use their stingers to paralyze zooplankton which are a few microns in size. The tentacles are even smaller than that, Mabee said.

The jellyfish are not harming other animals or the environment, but they are an example of how an exotic species can be easily moved from one place to another and populate a habitat that is not their own.

“Conservationists are always trying to avoid introductions of invasive species," Mabee said. "We are actively working to control the spread of other invasive animals and plants in the state, like bush honeysuckle or bighead carp."

Britny Cordera is a poet and journalist based in St. Louis and is currently serving as a newsroom intern at St. Louis Public Radio.

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