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Mysterious organisms should not hurt ponds
STARKVILLE, Miss. – Evidence that people are watching too many zombie shows or movies can be found in the concerns and questions pond owners have for biologists.
Several times a year distraught pond owners will call me for help identifying alien lifeforms that have landed in their ponds. Their descriptions can be shocking. “It’s the size of a basketball and looks like a gelatinous human brain!” Often, these demon creatures are attached to their pier or seem to be eating their fish habitat. Other times they have broken free and are appear to be watching from the water’s surface. It sounds almost like a horror film.
Fear not, good citizens of Planet Earth. These are not aliens hiding in your pond to take over the world. They are bryozoans, an ancient aquatic colonial organism not unlike corals of the oceans. Their name comes from Greek, meaning “moss animals,” although “gelatin animals” might be a better fit. Today, there are about 5,000 species of bryozoans, with most species found in marine waters. However, about 50 species show up in freshwater when water warms above 60 degrees in the late spring.
A single colony might consist of 100,000 animals or more, and that’s where it really gets interesting. Each colony starts from a single individual that settles on a submerged surface, which then begins to bud into new animals. For the scientifically inclined, these are called zooids. Thus, the colony is made up entirely of clones!
Each zooid secretes and lives within a nonliving case called a zooecium, but zooids stay connected to their neighbors by a small strand of protoplasm. This allows nutrients to be shared from one zooid to the next. Not having to feed themselves, some zooids will actually change form and become specialized to serve various purposes for the colony.
The colony mostly stays in one place, but some freshwater species can actually walk or glide slowly to new locations when necessary. New colonies are usually started by sexual reproduction, which produces larvae that settle on new surfaces to start clone colonies of their own.
The next question I usually get from the pond owner is, “How do I get rid of them?” My response is always the same, “Why do you want to?”
You see, bryozoans are filter feeders. They pull microscopic food from the water. This helps keep the pond clean. As filter feeders, they require clean water, so having bryozoans is usually a sign of good water quality and a healthy pond.
Of course, they can become a nuisance when they cover surfaces that you use. If that happens, manual removal is the best solution. Otherwise, let them do their thing. They are not hurting anything, and when water cools to below 60 degrees in the fall, the colonies will dissolve, and they will return to whatever planet they came from.
Don’t be surprised when they return next year.
Editor’s Note: Extension Outdoors is a column authored by several different experts in the Mississippi State University Extension Service.