Arctic sponges leave trails of spicules along the ocean floor

New research suggests ocean sponges aren't as sedentary as once thought.

Recent surveys of the Arctic seabed revealed trails of light brown sponge spicules, needle-like support elements in sea sponges. The discovery, detailed Monday in the journal Current Biology, suggests sponges are surprisingly mobile.

Until now, scientists assumed mobility was limited to the larval stage -- after young sponges locate a comfy spot on the seafloor, marine biologists estimated they settled down for life.

"We observed trails of densely interwoven spicules connected directly to the underside or lower flanks of sponge individuals, suggesting these trails are traces of motility of the sponges," researchers wrote in their newly published paper.

"This is the first time abundant sponge trails have been observed in situ and attributed to sponge mobility," the researchers wrote.

The research was led by Teresa M. Morganti, scientist at the Max Planck Institute of Marine Microbiology.

Sponges don't have any muscles or organs for moving around, but scientists have previously observed some evidence of mobility in the laboratory. Still, researchers had never before observed evidence of sponge migration in the ocean.

Scientists discovered the phenomenon after analyzing videos captured in 2016 by scientists aboard the research icebreaker Polarstern.

During the expedition, Polarstern towed a sled outfitted with a camera over the underwater peaks of the Langseth Ridge. Researchers also deployed a hybrid remotely operated vehicle, capturing images and video footage of massive sponge colonies.

Roughly 70 percent of the images analyzed during the recent survey revealed the presence of spicule trails. Though scientists spotted trails in areas with both dense and sparse sponge populations, they found the trails were more common in regions with large populations of small and juvenile sponges.

Researchers used 3D models to analyze the patterns of the interwoven spicule trails. The analysis showed the sponges occasionally change directions, according to the models, and regularly move uphill, battling gravity.

Authors of the new study estimate the sponges must regularly relocate to find sufficient amounts of food.

In the Arctic, conditions are harsh and resources are often scarce. It's also possible, scientists hypothesized, that young sponges move to find new mates and colonize new territory.

"Given the low primary production in this permanently ice-covered region, these trails may relate to feeding behavior and/or a strategy for dispersal of juveniles," researchers wrote. "Such trails may remain visible for long periods given the regionally low sedimentation rates."

Sponges are mysterious but hardy creatures, and have previously been discovered living beneath an Antarctic ice shelf, far from other life forms.

Many scientists are also interested in the study of sponges for their biochemical secrets, as they have yielded a variety of novel chemical compounds with potential for use in medicine.

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