By Graves Lovell
Biologist, Southeastern Pond Management

Every once in a while, we run across unusual and even bizarre things in lakes and ponds. Over the years, I've seen freshwater jellyfish, fish with two tails, Atlantic needlefish and bright orange phytoplankton blooms. One of the more unusual organisms I have encountered, although not completely uncommon, is an animal generically referred to as bryozoa.
On numerous occasions, usually in the summer months, I receive calls from concerned individuals regarding strange "jelly balls" in ponds:
"I've got these funny jelly looking things in my pond and I want to know where they came from. There are literally hundreds of them growing around the ends of sunken brush tops and they have completely covered the surface of an old sunken boat. I've never seen them in my pond before."
I recall first hearing about bryozoa in my "Introduction to Invertebrate Zoology" class at Auburn. We learned that this particular invertebrate was common to lakes and ponds. We were required to submit a collection of invertebrates at the end of the course. The professor reported that no student had collected bryozoa in quite some time, suggesting that it was somewhat rare. My experience dealing with lakes and ponds on a daily basis since would suggest otherwise.
So, I tell my concerned callers that they are describing a harmless invertebrate commonly found in lakes and ponds and not to worry about it; that it is safe to let out the dogs and kids.
These objects are not eggs of fish, frogs, or martians; nor are they the result of mutations caused by radioactivity from nuclear power plants. They are colonial invertebrates in the animal phylum Ectoprocta (bryozoa or "moss animals"). They are among the most commonly encountered animals that attach to submerged surfaces in freshwater. There are over 4,000 species of bryozoans (mostly marine). But for many biologists, bryozoans remain a biological oddity, with much of their ecology and physiology virtually unknown. The massive, gelatinous bryozoa, Pectinatella magnifica, is the largest of the roughly 50 freshwater species and is probably the most common bryozoan in lakes and ponds in the southeast. At maturity, the colony is commonly the size of a grapefruit or a small watermelon, however they can measure as large as two feet or more in diameter. This particular bryozoa is found in quiet ponds, lakes and slow-moving streams. They are usually attached to twigs, logs, rocks or even boat docks; however, they sometimes become unattached and can be found floating. Occasionally, summer plagues of large, floating bryozoans clog the water intakes of hydroelectric power plants so effectively that it requires full-time labor to keep them clear. They seem to prefer highly-organic pond and lake bottoms, whereas sandy and pebbly bottoms are poor habitat. Bryozoans often go unseen because they are sensitive to direct sunlight and are ofte
n found several feet below the surface, depending on water clarity. Although unrelated, bryozoans are similar in physiology to corals. Each bryozoa colony consists of thousands of zooids. These zooids each have tiny protrusions with a mouth and tentacles which create a current to filter the water for food particles. The rest of the body as well as the whole colony itself is encapsulated by a slimy, gelatinous covering called a zooecium. They can multiply several different ways, including the formation of highly resistant statoblasts (eggs) that enables them to over-winter and endure almost any period of adverse conditions. Adult colonies, however, usually die in the fall when the water temperature drops below 16 degrees C.
Where do they come from? Well, chiefly by virtue of their resistant statoblasts, bryozoans are one of the few freshwater animals that are capable of being transported from one body of water to another by animals. Statoblasts often occur in mud on the feet and feathers of waterfowl and in the fur of mammals. They are even capable of forming new colonies after passing through the digestive system of waterfowl, turtles, frogs and fish.
Although strange and sometimes frightening in appearance, these animals are absolutely harmless. In fact, bryozoans are thought to be useful indicators of water quality. Pectinatella magnifica, for example, is said to prefer eutrophic (highly fertile) ponds and lakes, whereas it would be less likely to occur in infertile or contaminated waters.
So, no need to worry, these critters are not that unusual after all. On the other hand, if you run across a talking fish...be sure and give me a call!
If you have any quests on fish or your ponds, call me @ Norman Latona at Southeastern Pond Management 205-664-5596.