Deep sea sponges are not known for their mobility. After all, they lack muscles, nervous systems and organs. And forget about fins or feet to tour the arctic seabed.
However, new research suggests that these ancient life forms can and can actually get around – and far more than marine biologists believed. While examining hundreds of photos and videos of Arctic sponges, scientists at the Max Planck Institute for Marine Microbiology in Germany discovered a vast web of traces that were several feet long in the creatures’ wake.
“Sponges are one of the most primitive forms of animal life,” said Dr. Teresa Morganti, who led the study published in Current Biology on Monday. “At the beginning we were very skeptical. We thought, ‘That is not possible. Sponges cannot move. ‘”
For the study, Dr. Morganti and her colleagues took underwater images of Langseth Ridge, a mountain range not far from the North Pole that is almost a mile below the permanently ice-covered surface of the water. Despite their initial skepticism, they found evidence that the wild sponges not only moved in their cold habitat, but also changed direction and even went uphill.
“They’re more active than we think,” said Rachel Downey, a deep-sea sponge expert at Australian National University who wasn’t involved in the new study. “We have never received such evidence before.”
In a handful of experiments, researchers have shown that at least some species of sponges are able to crawl slowly by contracting and expanding over days and weeks. “It’s one thing to know that a sponge is capable of doing this in a laboratory. Seeing it play out in the wild is a different thing, ”said Stephanie Archer, a marine ecologist at the Louisiana Universities Marine Consortium who was not a contributor to the paper.
In order to gain an insight into the extreme habitat of the deep-sea sponges, Dr. Morganti’s team on videos and pictures taken in 2016 by Polarstern, a research vessel and icebreaker.
The Polarstern footage showed a community of more than 10,000 sponges (ranging in diameter from a dime to that of a hula hoop) so dense that they almost covered the upper peaks of Langseth Ridge.
Underneath and between the animals are interwoven traces of spicules, skeletal structures that are thrown off by the sponges. The researchers found that spicula traces were visible in 70 percent of the hundreds of live sponge images examined for the study.
How and why sea sponges move in the deep polar sea remains open, said Dr. Morganti. It is very likely that they will wiggle toward food or away from their birth parents, she said.
Marine biologists are also unsure of the age of the Langseth Ridge Trails, as the habitat is largely undisturbed by water currents. Deep-sea sponges can live for decades, centuries, or even millennia, and previous laboratory studies have measured sponge movement at a rate of four millimeters per day or a few millimeters per month (whichever estimate you consult).
“A snail would be so much faster,” said Ms. Downey. “It is likely that at this moment there are thousands of sponges moving around the world. We just don’t see it. When it came to Langseth Ridge’s network of spicule trails, she said, “These trails can be stop-start, stop-start for decades or even hundreds of years.”
Dr. Morganti’s ongoing research aims to explain how exactly marine sponges manage to survive – let alone migrate – on the cold, dark, nutrient-poor peaks of barren underwater mountains near the North Pole. “How can these massive sponges survive in such an extreme environment?” She said.
The spicula traces provide tantalizing evidence that sponges (despite their anatomical simplicity) may sense environmental stimuli and move towards food.
And since the sponge species on Langseth Ridge are also found in waters off the coasts of Norway, Russia, Canada, Greenland and Iceland, their newfound mobility may also be more widespread.
“This reminded me of why I fell in love with sponges,” said Dr. Archer about the new knowledge. “Every time we think we’ve found them out, they surprise us.”