Bryozoans, ancient microscopic animals, thrive in Hayden Lake

Bryozoan colonies are often mistaken for masses of frog or fish eggs or even freshwater jellyfish, which are found in some local lakes. (Kathy Plonka)
Bryozoan colonies are often mistaken for masses of frog or fish eggs or even freshwater jellyfish, which are found in some local lakes. (Kathy Plonka)

Diane Lawrence couldn’t identify the gelatinous masses attached to the community dock in her Hayden Lake subdivision.

They were translucent with a jellyfish-like texture, and they kind of gave her the creeps.

“Sometimes, you see them free-floating in the lake,” Lawrence said. “They look like alien life forms.”

“Alien-looking” is a common description for bryozoans, freshwater colonies of microscopic animals that group together like coral. The colonies are thriving in local lakes this year, prompting calls from people who spend time on the water.

“I get a lot of calls from landowners like these folks in Hayden, wondering, ‘What is this thing?’ ” said Thomas Woolf, a program manager for the Idaho Department of Agriculture.

Bryozoans are an unusual but benign presence in local lakes, he said. They’re part of the varied life forms that teem below the water’s surface.

“I think they’re really cool, especially to show to kids,” Woolf said. “They’re neat, gooey, booger-like creatures that you don’t expect to see in the water.”

Because of their gelatinous nature, people often mistake the colonies for masses of frog or fish eggs, or even freshwater jellyfish, which also are found in some local lakes.

Bryozoan colonies are made up of individual animals called zooids, each about a millimeter long. They form jelly-like tubes that attach to submerged objects and sometimes are seen as floating spheres.

Under a microscope, the individual polyps are visible, along with the tentacles that direct food into the mouth, Woolf said. Bryozoans are filter feeders, sucking algae and decaying organic material out of the water, which benefits water quality.

They’re ancient animals, with a fossil record that predates dinosaurs. About 5,000 bryozoan species exist worldwide, with about 50 varieties inhabiting freshwater lakes.

Because they’re relatively unstudied in the Northwest, little is known about the types of bryozoans that live here, Woolf said. There’s even dispute about whether freshwater bryozoans are native to the Northwest.

Woolf has spotted bryozoans in the Coeur d’Alene River’s chain lakes, Lake Pend Oreille and Hayden Lake. Phil Cooper, a wildlife educator for Idaho Fish and Game, has received calls about them in Panhandle lakes since he moved here in the mid-1990s.

Bryozoans are also found in Eastern Washington, including lakes in Spokane County, said Chris Donley, Inland Fish Program manager for the Washington Department of Fish and Wildlife.

During certain years, bryozoans seem to experience exponential growth, with large colonies forming. That’s when agencies get flooded with calls from curious residents.

“Someone said there’s one in Hayden Lake the size of a Volkswagen, but I haven’t verified that,” Cooper said.

When cold weather sets in, the bryozoans will produce survival pods that contain a single zooid. Zooids in the pods can survive long periods of dormancy, including drying out and freezing. They start reproducing new colonies when the conditions are right.

The bryozoans that are so visible now will disappear as fall progresses, Woolf said.

“Once the water gets cold, they basically disintegrate and go away,” he said.

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