Published on 11/08/07

Mock 'jellyfish' sign of healthy pond

By Sharon Omahen
University of Georgia

If you see what look like jellyfish floating in Georgia ponds, don’t be alarmed. These are actually harmless moss animals called bryozoa.

“I get a lot of calls from pond owners who want me to come out and look at the ‘thing,’ ‘glob’ or ‘weird creature’ that’s under the surface of their ponds,” said Jim Crawford, the University of Georgia Cooperative Extension coordinator in Jefferson County.

Bryozoa are colonies of aquatic animals belonging to the phylum Ectoprocta, a group with fossil records dating back to the upper Cambrian period. Most live in saltwater, but one class, Phylactolaemata, lives exclusively in fresh water.

“Pectinatella magnifica is the type seen most often in our county ponds, and it consists of a mass of animals living on the surface of a gelatinous mass that is 99 percent water,” Crawford said. “There could easily be millions of interconnected animals forming this one colony.”

These colonies are firm and slimy to the touch and are most often attached to underwater limbs, pipes, logs, posts or even boat docks, he said.

UGA aquaculture specialist Gary Burtle has seen bryoza as large as baseballs, footballs and even basketballs.

“They are a food source for panfish such as bream and crappie,” he said. “They’re microscopic animals, and they form colonies for protection. When they’re football size, the bream can’t eat them.”

There are three ways to control bryoza populations, he said: physical removal, chemical control and fish control.

“If they’re large enough, you can scoop them out and take them to shore,” he said. “You can also add more panfish.”

Treating algae with herbicides containing copper sulfate will subsequently control bryoza, Burtle said.

“These bryoza have actually been in ponds for a while,” Crawford said. “But as the weather cools and the algae population recedes, the water becomes clear and they become highly visible. One pond had so many (bryozoa) they had attached themselves to the inside of the drainpipe. It actually became stopped up, and the water flow was down to a trickle.”

Saltwater species are known to grow on the bottoms of ships, causing drag and reducing the efficiency and maneuverability of the fouled ships.

“To me, they resemble a human brain. And that’s how I describe them to people on the phone,” he said. “If you take them out of the water and put them in the sun, the animals will dry out and die, leaving just the gelatinous material that looks like clear jelly.”

Bryozoa are a sign of a healthy pond. “Pond owners should be fascinated that their pond is clean enough to support these prehistoric animal colonies,” he said. Burtle agrees.

“They’re one of those anomalies that people just don’t understand,” Burtle said. “They’re on the same evolutionary scale as jellyfish, and they can’t hurt you.”

“These freshwater bryozoa are completely harmless in and of themselves, except when they occasionally clog water pipes,” Crawford said. “If you have some close to your boat dock, they probably make interesting conversation pieces.”

Sharon Omahen is a news editor with the University of Georgia College of Agricultural and Environmental Sciences.