When you hear of jellyfish, you probably think of the ocean and the fact that you don’t want to be stung by one. But did you know there are freshwater jellyfish as well? And that they’ve been in the lake at Bays Mountain Park for at least 30 years?
“It’s true,” explains Bob Culler, a park ranger at Bays Mountain. “There really is such a thing as a freshwater jellyfish.”
These little critters live in freshwater lakes and rivers all around the world, and during most times of the year they exist as polyps attached to rocks and logs on the bottom. The polyps can exist indefinitely and they reproduce asexually, growing to pretty large numbers fairly quickly when the water conditions are right and there’s plenty of food to eat.
However, when the water temperature reaches a certain point, Culler said, the polyps then transform into the jellyfish stage of their life.
“That’s when we see them. Usually in late August or early September. They’ll most likely come out after we’ve had a hot, dry summer,” Culler said. “They’re about the size of a nickel to a quarter, and they’re clear except for the white cross on their back. That’s the part you see pulsing through the water.”
After the polyps become jellyfish, they live about three weeks and then die. Though for the time they are alive as jellyfish, Culler said, they can be found close to the surface all across the 44-acre lake. The water is clear most of the time, and the creatures can be seen as deep as three or four feet most days.
“We’ve known they’ve been here at least 30 years, though it could have been longer,” Culler said. “Nobody knows how they got here. Probably carried by birds is the standing theory, by ducks or some other waterfowl. It may take years to get the population up to where a body would notice them, but it only takes one.”
The jellyfish are just another thing in the lake and best Culler can tell, nothing eats them. Maybe because they don’t taste good or because of their mild stinger. They do eat plankton and water fleas and don’t have an effect one way or the other on the water or the wildlife.
If you’re thinking about catching one and putting it in an aquarium, you might want to reconsider. Culler said the jellyfish are hard to keep alive, and they’re only going to live for a few weeks at best.
“Jellyfish are almost all water, they’re very delicate and you have to set up a special system to keep one alive,” Culler said.
So if you’re interested in seeing a freshwater jellyfish firsthand, go up to Bays Mountain Park this fall, walk along the dam or take a barge ride. You might just spot one bobbing along in the water.
Facts about freshwater jellyfish
• Freshwater jellyfish lack a head and skeleton and contain no special organs for respiration or excretion. The body is made of 99 percent water.
• Though small and practically see-through, they are easy to spot on sunny days as they tend to surface in large groups called blooms.
• Their large, flat sex organs — called gonads — are the only parts of the creatures that are not translucent.
• They tend to stay near the bottom of shallow waters where they can conserve their energy for capturing food or escaping predators.
• They feed on super tiny aquatic animals called zooplankton.
• They are rich in protein and are eaten in many cultures around the world.
Source: The Nature Conservancy