They Came from the Lake

Published on: Jul. 3, 2009

blobOdd-looking gelatinous blobs are appearing in some Missouri lakes and ponds. I’ve been contacted twice in the last week by persons observing them and wondering what they are. They may remind you of the jellyfish that you have seen in the ocean. There is nothing to fear from these colonial, invertebrate animals called bryozoans. They are from this world.

Most bryozoans live in saltwater environments, and they build stony skeletons similar to those of corals. There is one group of bryozoan species that live in freshwater habitats, including Missouri’s lakes, ponds and streams. Worldwide, bryozoans are found on every continent except Antarctica.

The tiny (about 1mm long) individuals in a colony, called zooids, are filter feeders. They extract plankton, bacteria and detritus from the water and help to recycle nutrients in the water. Their colonies can form gelatinous masses as large as basketballs, although they typically are closer to the size of a softball. Colonies may be found free-floating or attached to submerged rocks, dock supports, logs, plastic debris or vegetation.

Bryozoans can reproduce by several methods. They can form small structures, called statoblasts, which are easily transported to new water bodies by waterfowl. The statoblasts can remain dormant for years and become active again when conditions are good for growth. Colonies can also reproduce by pinching off portions of their gelatinous, zooid-containing material that can grow into another colony.

Although strange-looking, bryozoans are harmless and their presence usually indicates good water quality, as they are intolerant of pollution or muddy water. They can become a nuisance only if they attach to the inside of pipes or filters and impede the normal flow of water.

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