What Are The Jelly-Like Blobs Under My Dock?

The Bryozoan Species

Have you ever noticed jelly-like blobs attached to a dock on a freshwater lake? At first glance, they appear to be brown fish egg sacks, but what are they?

Typically, when people ask this question, what they have discovered is a colony of the freshwater bryozoan Pectinatella magnifica. Freshwater bryozoans are microscopic aquatic invertebrates that live in colonies that can form into jelly-like clumps, and are often found attached to docks or sticks. Bryozoan colonies can be as big as one foot (30 centimeters) in diameter. The base of each tiny bryozoan is attached to a surface. Its body has an outer sleeve-like structure called the cystid, and a mass of organs called polypide that moves inside of it. 

Pros of the Jelly-Like Blobs:

Bryozoans live in colonies, and they’re filter feeders, so they eat algae and other small creatures.

They’re native to our region – and even better, they require clean water. So if you find them in your lake, it signals that you have a healthy aquatic environment. 

Cons of the Jelly-Like Blobs:

They can attach to pond fountains and block the intake on the pump. Filters like the PondSelect Mesh Cage* we sell with a large surface area can be the solution. These filters keep the jelly balls or Bryozoans away from the pumps intake while still allowing water to flow through the filter.

The opening at the top of the cystid allows the polypide to slide out toward the water. This exposes a head-like structure called lophophore topped with tentacles that filter food from the water. The slightest disturbance will cause the polypide and tentacles to retract quickly. The mucous-coated tentacles capture diatoms and other microscopic organisms. The microscopic organisms are then swept into the mouth by tiny hairs called cilia that layer the tentacles.

It’s unclear how bryozoans are related to other invertebrates. Bryozoans are not a close relative of other groups and likely evolved from a marine worm that adapted to a sessile existence. Fossil bryozoans first appear in Cambrian rocks, which is late in the fossil record. They likely existed earlier, but in softer form that did not secrete calcareous exoskeletons that leave fossil evidence.

Where the Species Comes From

They are not a close relative of coral. However, bryozoans are similar in that they are small colonial aquatic species that effectively filter particles from the water. These large jelly blobs in freshwater are native to North America, and they typically grow on docks and other submerged wood.

There are several ways that bryozoans can reproduce. Zooids can multiply themselves by budding, and they also grow eggs and sperm to reproduce. Larval forms will go through complete metamorphosis. Freshwater bryozoans form hard, round statoblasts inside their bodies and act like seeds.

During the summer months, these jelly blobs release small larvae that disperse and establish new colonies nearby. During the autumn season, each colony produces thousands of small seed-like disks that remain dormant during the winter, and will germinate the following spring.

Potential Problems with Bryozoan

Most other freshwater bryozoan species develop branching tubules that look like brown moss in the water (Bryozoa = “moss animal”). While freshwater bryozoans improve the quality of the water, some species become a serious problem when they clog the irrigation and intake pipes. Others carry parasites from certain species of myxozoan invertebrates. This can cause proliferative kidney disease in salmon and their relatives. This species maybe causing problems in your pond if they are present.

*The PondSelect Mesh Cage is sold as a product add-on that fits all of PondSelect Pond Fountains. We offer a hard or soft cage option.

Ask Us Anything

If you have any questions related to your pond that we can help you with, just let us know!

Please enter your email, and we'll follow up with you as soon as we can.