Sea sponges survive in the Arctic by feasting on extinct creatures

The bottom of the Arctic Ocean is not the easiest of places to live in. Nutrients and vegetation are very scarce, it’s cold, it’s dark, the elements are pretty much against you. That’s why researchers were very surprised to find a dense population of sponges alive and kicking in the volcanic seamounts of the ocean. As it turns out, they were feeding off fossilized remains of extinct animals and fauna.

Image credit: The researchers.

Researchers from Germany’s Alfred Wegener Institute were around 200 miles from the North Pole on board their research vessel when a submarine camera they were towing caught sight of fuzzy sponges on top of the extinct volcanoes. They just couldn’t believe it. Some of the sponges even stretched over three feet (one meter) across — very big for sponge standards. 

Sponges don’t have a digestive tract, so they rely on passive filter feeding to collect nutrients from water passing through them. Ocean currents in the Arctic Ocean are slow, with not many particles swirling in the water. This made the sighting even more unusual, especially considering tests showed the average sponge was 300 years old. How were they surviving there, for centuries, in what was basically an ocean wasteland?

Studying the sponges

The researchers collected samples of the organisms and the sediment around them and sent the samples to the lab for examination. The analysis showed the seafloor wasn’t as desolate as thought. In fact, the sediment samples were full of fossils. 

The fossils were the empty shells of large deep-sea worms. While they don’t live there anymore, the researchers weren’t surprised to find the shells. Many years ago, gases leaked from the vents of the submerged volcanoes, creating a perfect habitat for the worms. That dynamic ecosystem from a long time ago is still influencing the area. 

The samples collected suggest the sponges are packed with microbial bacteria, with which they form a symbiotic relationship. The bacteria break down the ancient leftovers that then the sponges use to obtain nutrients from. The researchers spotted different sizes of sponges, with the average measuring 30 centimeters or 12 inches.

“This allows them to feed on the remnants of former, now extinct inhabitants of the seamounts, such as the tubes of worms composed of protein and chitin and other trapped detritus,” said first study author Teresa Morganti, a sponge expert from the Max Planck Institute for Marine Microbiology in Bremen, Germany, in a statement.

The researchers believe that there could be more sponge grounds similar to this one along the volcanic ridge of the Arctic Ocean. This would be good news for many other creatures that live there because sponges are natural ecosystem engineers. As they grow, they create places for other animals to live in, depositing a sticky surface for bacteria to settle on. 

A better understanding these ecosystems is essential to protect and manage the diversity of the Arctic Sea, which is currently under serious pressure, the researchers stress. With the sea ice retreating at record rates, the researchers want that the web of life in the Arctic Sea is under pressure. Both the sea ice and its thickness have shown a big decline, affecting the oceanic environment. 

Last year, another group of researchers found sponges below the Antarctic ice shelves while drilling in the Filchner-Ronne Ice Shelf neat the southeastern Weddell Sea. It was an accidental discovery that left the researchers perplexed, calling for further studies (like this one) to better understand what’s actually going on below the Arctic Sea. 

The study was published in the journal Nature

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