On the Move: Deep Sea Sponges
By: Alexandrya Robinson

When thinking about the deep ocean floor, pictures may come to mind of barren hills of sand, maybe dotted with the occasional prints from crab legs. But other organisms call the depths their home, and recently one phylum has been the source of discussion: sponges. Sponges are simple, multicellular filter-feeding organisms with no tissue diversification.

Scientists from the Helmholtz Centre for Polar and Marine Research, after looking at high resolution images of arctic depths, found mysterious tracks across the ocean floor that baffled them until they followed those tracks, which led to sponges, showing evidence of mobility.

Sponges were previously accepted as sessile organisms that sometimes passively moved from one area to another, transported by other organisms or even water currents. However, in deep arctic water, where these images were taken, there are no strong currents. That, coupled with an almost snail-like ooze trail, were definite indicators of the sponge’s path. These images provide new evidence that sponges are not as immobile as previously thought. 69% of the images taken by the Helmholtz Centre for Polar and Marine Research showed these trails, meaning this is not just an isolated occurrence.

How was this fact missed for so many years? The answer to that is simply the time intervals of observation. Because sponges move very slowly, while lab experiments have observed contraction and relaxation of the sponge’s skeleton which can cause movement up to four millimeters a day, this phenomenon has not been seen in the wild until this point due simply to the time scientists can realistically spend observing individual sponges in the wild. Sponge movement is already an odd concept due to the lack of muscle tissues in Phylum Porifera. The skeletons of sponges are very dense and, in some cases, highly rigid.

The question, then, is how these sponges are moving and why. Currently there is no definitive explanation, only the hypothesis that sponges are moving around the ocean to potentially seek out sources of food, move away from poor conditions, or to disseminate their offspring. Sponges are incredibly important to deep-sea ecosystems, and this new information is another piece of the puzzle scientists are hoping to understand.