If you have seen one of these in your pond, you’ve seen a phylactolaemate bryozoan, an animal that has inhabited our planet for millions of years. Though there are several thousand species of bryozoan, the phylactolaemate bryozoan is exclusively found in freshwater and, currently, there less than a hundred named species. Bryozoans make their home on underwater structures such as fallen branches.
The colony begins with one zooid which will reproduce to form copies of itself. Every member of the colony is a genetic copy of the first. Bryozoans reproduce through both sexual and asexual means such as fragmentation. The freshwater phylactolaemate bryozoan also form statoblasts through asexual means. These statoblasts become encased in a shell like covering and will either be carried away from the parent colony to regrow in a different location or may remain attached to the parent colony to rebuild when the parent colony dies off. New colonies are produced through sexual means, however. Bryozoans, believed to be hermaphroditic, produce larvae that will detach from the parent colony and float or be carried to a new location to form a new colony.
Generally, the bryozoans will remain under the water unnoticed by pond owners. However, when the summer draws to a close and the water temperatures drop you may see colonies floating in the water. This happens when individuals die and gasses build up which make the colony float. Bryozoans are generally not harmful and can be a food source for other animals. They can, however, cause problems in watergardens or closed systems if they become lodged in filters or pumps. If bryozoans become an issue or are an eyesore, the colony can be removed by hand. Bryozoans will most likely return the following year, however, as buds or statoblasts have already attached elsewhere to begin another colony.
If you have questions about these odd creatures, ask your Aquatic Specialist or contact AQUA DOC at 800-689-5253.