What’s A Bryozoan?

First time you see a bryozoan clinging to a dock or fallen tree limb in shallow areas, you’ll wonder if you should run yellow caution tape and call the Environmental Protection Agency or a hazmat team. Before you panic, let’s examine this jelly-like blob that resembles something from outer space. These critters are moss animals. They look alien, but can be beneficial.

Some freshwater varieties are considered useful indicators of water quality. Scientists say they like water that is eutrophic (rich in nutrients which cause excessive growth of aquatic plants). Freshwater bryozoans live in colonies and can get as big as basketballs. Since they’re aquatic animals, they digest microscopic creatures like plankton by filtering water. They’ve been around 400 to 500 million years.

Bryozoans contribute positive and negative effects. Positively, they may circulate nutrients and deliver food to other organisms. Negatively, they can grow on pipes, thereby, disrupting drainage and irrigation systems.

At the end of the summer, as lake temperatures cool, bryozoans die. The jelly dissolves releasing small, dark brown disks. The disks remain dormant for some time, withstand drying or freezing, and survive winter to start new colonies next year. While appearing ominous, they typically pose no threat to lake users.

Over 4,000 living species are known. One genus is solitary. The rest are colonial. A few species can creep very slowly using spiny defensive zooids as legs. Zooids are any organic body or cell capable of spontaneous movement and existence more or less apart from, or independent of, the parent organism.

Zooids of all freshwater species are simultaneous hermaphrodites. Although many marine species function first as males, and then females, their colonies always contain a combination of zooids that are in male and female stages. In some species, larvae have large yolks, go to feed, and quickly settle on a surface. Others produce larvae that have little yolks, but swim and feed for a few days before settling. After settling, all larvae undergo a radical metamorphosis that destroys and rebuilds almost all internal tissues. Freshwater species also produce statoblasts (encased cells that can survive unfavorable conditions). They lie dormant until conditions are favorable, which enables a colony’s lineage to survive even if severe conditions kill the mother colony.

Freshwater bryozoans are preyed on by snails, insects, and fish. Chemicals extracted from a marine bryozoan species have been investigated for treatment of cancer and Alzheimer’s, but analysis has not revealed productive results.

Mineralized bryozoan skeletons first appeared in rocks making them the last major phylum (large group of related animals or plants) to appear in a fossil record. This has led researchers to suspect bryozoans arose earlier, but were initially unmineralized, and may have differed significantly from fossilized and modern forms. Early fossils are mainly of erect forms. Encrusting forms gradually became dominant.