|Blob growing on dock flotation|
The water quality office phone rang last week and Gopala Borchelt, Executive Director of Table Rock Lake Water Quality answered. A local lake resident wanted to know what in the world was growing on their dock and could it be the result of some lake contamination or sewer overflow. Maybe a space alien! Since the dock was nearby, Gopala jumped in the car with camera in hand to see what was up. It turns out the strange blob is not the result of any pollution or invasion but a strange creature that is actually working to help us keep the lake clean.
The blob is a bryozoan colony. Pectinatella magnifica is a member of the animal phylum Ectoprocta (common names: bryozoans, moss animals), a group with a fossil record extending back to the upper Cambrian (500,000,000 years ago!). The majority of bryozoans are marine (several thousand species), but one class, the Phylactolaemata, is found exclusively in fresh water. The species of this class is what is found in our area lakes. The basic ground plan of a bryozoan superficially appears to have more in common with a coral; they are, in fact, ecological analogs. Bryozoans and corals are in different phyla and are unrelated. What seems to be an individual is actually a colony of zooids (not polyps as in corals). Each zooid has whorls of delicate feeding tentacles swaying slowly in the water catching food.
Bryozoan scraped off into a dip net
Though they are not closely related to corals, bryozoans are superficially similar in that they are tiny colonial aquatic creatures that effectively filter particles from the water. The large gelatinous species is native to North America and often grows on docks and other submerged wood. During the summer it releases small larvae that swim away and establish new colonies nearby. In the fall each colony produces thousands of tiny, seed-like disks that remain dormant over winter and germinate the following spring. Most other freshwater bryozoan species form branching tubules that resemble brown moss in the water (Bryozoa = "moss animal"). While freshwater bryozoans improve water quality, some species become a serious nuisance when they clog intake and irrigation pipes. I, for one, am glad for the help the bryozoans are providing in keeping the lakes clean!
|Holding a bryozoan (gloves help - it is slimy!)|
Quote of the Week
Ocean: A body of water occupying about two-thirds of a world made for man - who has no gills. -Ambrose Bierce