Arctic sponges are rolling stones | Polarjournal
Sponges leave traces on the seabed of the deep sea. Until now, science assumed that the animals were sessile. The tracks to live sponges suggest that the animals could be actively moving. The underwater images were taken by researchers of the Alfred Wegener Institute on a Polarstern expedition in the Arctic with the help of the OFOBS (Ocean Floor Observation and Bathymetry System). (Photo: AWI OFOBS Team PS101)

Sponges: They are considered to be one of the most primitive forms of animal life, because they have neither locomotion organs nor a nervous system. A team around deep-sea scientist Antje Boetius has now discovered that sponges leave trails on the sea floor in the Arctic deep sea. They conclude that the animals might move actively – even if only a few centimetres per year. They are now publishing these unique findings in the journal Current Biology.

The surprise was great when researchers looked at high-resolution images of the sea floor of the Arctic deep sea in detail: Path-like tracks across the sediments ended where sponges were located. These trails were observed to run in all directions, including uphill. “We conclude from this that the sponges might actively move across the sea floor and leave these traces as a result of their movement,” reports Dr Teresa Morganti, sponge expert from the Max Planck Institute for Marine Microbiology in Bremen. This is particularly exciting because science had previously assumed that most sponges are attached to the seafloor or are passively moved by ocean currents and, usually down slopes.

The images published in the study show the movement patterns (red) and the individual sponges (purple arrows). The pictures above show that the sponges are sitting on organic material and that the tracks had partially formed large circles (white arrows). Image: from Morganti et al (2021) Current Biology

“There are no strong currents in the Arctic deep sea that could explain the structures found on the sea floor,” explains expedition leader Prof. Antje Boetius, who works together with deep-sea biologist Dr Autun Purser from the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI) in the HGF-MPG Joint Research Group for Deep-Sea Ecology and Technology. The recently published recordings were made during an expedition at 87 °North at the Karasik Seamount about 350 kilometres away from the North Pole with the research icebreaker Polarstern in 2016 with a towed camera system OFOBS (Ocean Floor Observation and Bathymetry System). “With OFOBS we can create 3D models from the deep sea. The seamount’s summit was densely populated with sponges. 69 percent of our images showed trails of sponge spicules, many of which led to live animals,” reports Autun Purser.

Video footage from the OFOBS system shows deep-sea sponges on the Arctic seafloor. The traces left by the animals are also partly visible. Video: Youtube AWI

Many questions arise from these observations: Why do the sponges move? How do they orient themselves? Possible reasons for locomotion could be foraging, avoiding unfavourable environmental conditions, or to distribute offspring. Searching for food in particular plays a major role in nutrient-poor ecosystems such as the Arctic deep sea. Sponges have an important function there anyway. Sponges also provide arctic fish and shrimp useful structures to use as a habitat. However, the scientists still have to investigate the mechanisms of locomotion.

Press service AWI

Link to the study: Teresa M. Morganti, Autun Purser, Hans Tore Rapp, Christopher R. German, Michael V. Jakuba, Laura Hehemann, Jonas Blendl, Beate M. Slaby, Antje Boetius: In situ observation of sponge trails suggests common sponge locomotion in the deep central Arctic. Current Biology (2021); DOI: 10.1016/j.cub.2021.03.014

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