What is this Jelly-like Blob Under My Dock?

The Question: I was swimming in the lake behind our house with a friend one day and we found a thing attached to our dock and it appeared to be brown fish egg sacks. But with closer observation it turns out to be a jelly like substance. What is it?

Submitted by: Kali, Tennessee

(click on photos and graphics to expand)

"Pectinatella magnifica 8568" by Jomegat
Freshwater bryozoan (photo by Jomegat)

The Short Answer: Without any other information or photos, it’s hard to be definitive about this, but usually, when people ask this question, what they have found is colony of the freshwater bryozoan Pectinatella magnifica. Freshwater bryozoans are tiny colonial animals that can form jelly-like masses, which are often found attached to sticks or docks.  Bryozoan colonies can be as much as a foot (30 cm) in diameter.

This Youtube video shows a couple of very nice bryozoans blobs: http://www.youtube.com/watch?v=g1H3e0Iynso

Pectinatella magnifica (photo by Triclops200)
Pectinatella magnifica (photo by Triclops200)
Pectinatella magnifica
Pectinatella magnifica

More Information: 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.  For further information on freshwater bryozoans, the site of Dr. Timothy Wood at Wright State is very helpful: http://www.wright.edu/~tim.wood/bryozoans.html. (My thanks to Dr. Wood for his help in preparing this answer.)


This Youtube video shows a very nice view of a bryozoan filtering food particles out of the water: http://www.youtube.com/watch?v=utPtyceR_YY&feature=related

Cite this article as: Pelletier, TC. (September 16, 2010). What is this Jelly-like Blob Under My Dock? Retrieved from https://askanaturalist.com/jelly-like-blob-under-my-dock/ on December 15, 2018.

60 thoughts on “What is this Jelly-like Blob Under My Dock?”

  1. Hi Elissa, they sound like bryozoans. Can you email a picture to me? This is the time of year when they are large and everyone is seeing them. But they’re always around. You can just leave them alone. Tom

  2. yeah, they are GOOD things, leave them alone, let them do their thing, which is clean the water. 🙂

  3. We found one under our dock at Lake Land’Or in Ladysmith,
    Virginia. Huge…thanks for the explanation and advice tha they
    are harmless.

  4. We have 2 of these masses on our shoreline. While canoeing along the shore we saw many many more. Are they a hazard to people when they hatch? This is the first year I have seen them in out Lake. Big Mink Lake in Hastings Highlands On. I took pictures but don’t know how to post them here. They are the same as picture above of the bryozoan.

  5. Hi Valda, they are completely harmless. They don’t hatch into anything. In fact, once the water gets colder, they disintegrate and form many tiny statoblasts that fall to the bottom. In the spring, the surviving statoblasts begin growing again. Tom

  6. Hi Tom. I know what musicians are. We find them in our wetlands at Roger Williams Park Zoo in Providence, RI. But my son saw something similar up in Maine which was clear and growing on the foam under their raft. Do you think it may have been an immature colony? Do they attach themselves to inorganic substances? He said it was about a 20 inch long mass. It had cellular water-filled compartments which squirted when pinched.

  7. A friend of mine just found these on the ladder of her dock and would like to remove them but was not sure what they were until I found your site here. Can she carefully scrape them off and let them drift in the water to find a new anchor spot without harming them? Or is there a better way to do this?

  8. Yes, you can remove them. They are about to die back when the water gets cold anyway. You could try taking a stick and poking it through the middle and then prop the stick somehow so the colony is off the bottom, but I’m not sure how critical that is. I would just scrape if off if you want and not worry about it. Tom

  9. Hi Rose, I’m trying to figure out what you meant by “musicians.” Are you talking about a salt water dock or a fresh water dock? Did he take any photos?

  10. Hi, we recently anchored near Pickwick state park on Pickwick Lake, Tennessee, in the morning we had jelly like creatures on the boat with a pale blue tint. These creatures were found at the highest point of the boat and were about the size of a quarter. When they dried out they were a small dark blue spot. what is it.

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