You’ve just had a relaxing swim and reach for the ladder on your dock when your hand grazes across what can only be described as a gelatinous mutated blob straight out of a Sci-Fi alien horror flick. Don’t worry though, these masses aren’t alien hatchlings prepared for the takeover all that inhabit the earth…

I get a number of calls and emails this time of year about “alien-like” life forms growing from docks, submersed tree limbs and other abiotic material in the lakes. “What are they?!?! and more importantly, what can we do with THEM?!?!?” are common questions I get. Today we will take about what THEY really are.

Bryozoans, or moss animals, are actually a group of small, filter feeding animals living in a colony that most often attach to anything they can for anchoring. These animals are not new to the world being a part of the phylum Ectoprocta which has a fossil record dating back 500 million years ago! Each colony is made up of individuals known as “zooids”, each with a specific function in the colony. For example, some zooids (autozooids) are responsible or feeding, while others are tasked for defense and reproduction. Worldwide, there are more than 4,000 species of bryozoan, most of which are marine species, but there are around 50 that make their home in freshwater. Bryozoans come in a variety of shapes and sizes, with marine bryozoans more closely resembling corals.

The most common bryozoan found native east of the Mississippi is Pectinata magnifica, also known as the magnificent bryozoan. P. magnifica grows in large, gelatinous masses and are often mistaken for the eggs of fish or reptiles. While relatively little is known about freshwater bryozoans, they are among the most common sessile aquatic animals and are extremely important filter feeders (like mussels) and are most often found in eutrophic systems. Filter feeders are extremely important in that they remove suspended matter from water, in turn, clarifying that water. The visible portions of the animal, the lophophores, extend small arms into the water to catch suspended matter and nutrients. When disturbed, these structures all quickly recede back into the gelatinous mass. P. magnifica undergoes asexual reproduction, producing new colonies of genetically identical organisms to the parent. When looking at P. magnifica, you will notice a number of black “dots”. The black dots are actually statoblasts that are released into the system when the rest of the mass of zooids dies off. These statoblasts then attach to other substrate and form new colonies. P. magnifica also provide food for various snails, insects and fish.

Some saltwater bryozoans have been known to cause a severe skin itch in fisherman. However, despite their menacing appearance, freshwater bryozoans rarely cause issues for humans other than becoming a nuisance in water pipes, sewage treatment facilities and power generation stations. P. magnifica is actually thought to be an indicator of water quality in eutrophic reservoir systems like those of Lake Gaston and Kerr Lake. There are organisms that parasitize some freshwater bryozoans and can cause kidney disease in salmonid fish. This organism has reduced fish populations in some North American waterbodies, but this is not at the fault of the Bryozoans.

If you have any further questions about bryozoans, specifically P. magnifica, please visit the web links for additional information.

Photo credit: Justin Nawrocki, NCSU Aquatics

Original Post: 06/17/2013

Web Links For Additional Information:
Bryozoa – NCSU Extension