We have jellyfish in Missouri. For some, occasionally viewing these unusual creatures is a thrill while a frightening sight for others. Many compare freshwater jellyfish to ocean versions that are considerably bigger with a stinger that burns on contact.
The translucent, dime-sized freshwater jellyfish are not harmful to humans like their counterparts in the ocean. The tiny stinging cells on tentacles of freshwater jellyfish are used to paralyze microscopic animals called zooplankton in the water with their ring of 400 slender tentacles. The jellyfish then consumes immobilized prey for nourishment. Sound scary? Not for humans!
"I've held them in my hand, and the cells are either too small or too weak to hurt a person," said Greg Stoner, fisheries biologist at the Missouri Department of Conservation. “They look just like ocean jellyfish with an important difference – stinging capabilities. Freshwater jellyfish have the same stinging cells as ocean jellyfish, but not to the same extent.”
According to the Missouri Department of Conservation website, freshwater jellyfish likely originated in China, but the species was first described by a researcher in England during 1880. It has been reported in lakes, old quarries and ponds in the United States for more than 100 years.
“How much freshwater jellyfish affect the productivity of a fishery is unclear,” Stoner said. “When jellyfish are placed into an aquarium containing fish, the fish readily attempt to eat them but then quickly reject them. Anglers have reported a decrease of fishing success when jellyfish were present. Also, fin damage and death of young fish due to contact with the tentacles have been observed in the laboratory.”
Crayfish apparently find freshwater jellyfish appealing. When Conservation Department officials put jellyfish into aquariums containing crayfish, the crayfish consumed the jellyfish like a child eating chocolate.
So how did freshwater jellyfish show up in Missouri? They enter new habitats as polyps stuck to vegetation, birds, or transported in bait buckets. Jellyfish like to live in lakes with good water quality, and they usually hang out near the bottom and are not generally seen in fast flowing streams or rivers.
The best time to seek out a freshwater jellyfish would be in a calm water on a nice sunny day. Most sightings have generally been during August or September months. These unusual creatures usually surface in a “bloom” of many jellyfish packed together.
So next time you see a jellyfish in Missouri, take a good look and don’t be frightened. They couldn’t hurt you if they wanted to.
That said, we have another creature in Missouri that people often confuse for a jellyfish. A reader recently sent me a photo of a blob-like creature while asking if it was a jellyfish. I did not know and started researching. Here is what I found:
The blob was a freshwater bryozoa and they are common in Missouri. Colonies of this harmless aquatic animal can grow big as a basketball, sometimes called “moss animals.” Colonies of this species might take different forms or colors to blend in with their surroundings.
Bryozoa are strange, slimy masses that can range in color from clear to green or yellow to dark brown. Their slimy, jellyfish like bodies often makes them mistaken for a freshwater jellyfish, a considerably smaller creature.
Bryozoa are found in ponds, lakes and slow streams. They often attach to vegetation or the undersides of logs, pilings and docks to avoid bright sunlight. Bryozoans filter water for their food, feed on small microorganisms, and are indicators of good water quality. Snails, insects and fish may prey on bryozoans, but the predation is not extensive.
Normally, the colony dies out by late fall, when they are often found as they break up and wash up on shore. Individual eggs are released as winter-hardened “seeds” and may be carried to other waterways on the feet of aquatic animals.
Although about 20 species of bryozoans are found in oceans, one class, Phylactolaemata, lives only in fresh water. Our freshwater version usually prefer the rather quiet waters of lakes, ponds and swamps, but some live in streams. Most bryozoan colonies are attached to some object, like a rock, dock support or tree branch, and most form in spring and die away in winter. Colonies reach their largest size in late summer and fall, which is when most people notice them.
Freshwater bryozoans are harmless, though they occasionally clog water pipes and sewage treatment equipment. Bryozoans eat microscopic organisms and are eaten by several larger aquatic predators, including fish and insects. Like mussels and other filter feeders, bryophytes gradually cleanse the water as they feed.
So, the old outdoor writer learned something new and hopefully you did too. Thanks to the Missouri Department of Conservation for the bulk of this information.
Kenneth Kieser, a veteran outdoors writer and member of the Waterfowlers Hall of Fame and National Fresh Water Fishing Hall of Fame, writes a weekly outdoors column for The Examiner. Reach him at firstname.lastname@example.org