Deep-sea creature — with ‘oar-like’ legs — seen eating odd meal miles below surface

Miles below the surface of the ocean, it’s pitch-black, cold and empty.

Only the highly adapted and most unique creatures on Earth can survive there, and even then, much of their lives are a mystery.

That’s why researchers from the Woods Hole Oceanographic Institution, University of Montana, SUNY Geneseo, Willamette University and the University of Rhode Island joined forces to shed light on the dark underworld.

Using a “Deep Submergence Vehicle” named Alvin, researchers explored the deep-sea trench off the northern coast of Puerto Rico over the course of 14 dives, according to a study published Sept. 11 in the peer-reviewed journal Proceedings of the Royal Society B.

“Using the submersible Alvin, scientists encountered (an) isopod swimming 3.7 miles deep , with oar-like legs as long as your fingers, eating an unexpected food source,” according to a Sept. 11 news release from the Woods Hole Oceanographic Institute.

The isopod, identified as Bathyopsurus nybelini, had a body that was “transparent and thin, of parchment-like consistency, (and) with highly fragile appendages,” according to the study.

The animal itself was not a strange find, researchers said, but what it was holding caught their interest.

“Surprisingly, these isopods can be seen carrying something more common on the ocean’s surface: large pieces of Sargassum algae,” according to the institute. “At the surface, Sargassum grows using photosynthesis, forming floating forests of algae.”

This meant the algae had grown at the surface, then sank nearly four miles toward the seafloor before it was snatched and eaten by the isopod, researchers said.

“The isopod waits, specially adapted to find and feed on this sunken source of nutrients,” the institute said. “These findings of a deep-ocean animal relying on sinking food from waters miles above underscore how closely connected the surface ocean is to the deep ocean.”

A video of the encounter was shared Sept. 12 by the institute on social media.

Study author Mackenzie Gerringer, from SUNY Geneseo, said “deep-ocean ecosystems seem like harsh environments, but the animals living in these habitats are well-suited to meet these conditions. This isopod illustrates that an animal in a dark and high-pressure environment at the bottom of the seafloor has evolved multiple adaptations to feed on algae that grow in a sunlit ecosystem.”

Part of that adaptation is the swimming technique of the isopod, researchers said.

Using large, paddle-like legs, the isopod swims upside down and backward through the water, according to the study. This technique allows the isopod to pick up and carry fronds of Sargassum off the seafloor, rather than trying to catch them in the water column.

“The isopod also possesses serrated and grinding mouthparts, ideal for tearing and consuming the tough Sargassum, and has bacteria in its gut to assist digestion,” the institute said.

Researchers said there has been an increase in Sargassum growth in recent seasons as climate change contributes to large blooms that ecologically and economically impact the Caribbean communities.

“Life everywhere, even in the deepest depths of the sea, is inexorably connected to the microorganisms around it,” said Logan Peoples, study author and microbial ecologist with the Flathead Lake Biological Station.

The research team includes Peoples, Gerringer, Johanna N. J. Weston, Rosa León-Zayas, Abisage Sekarore, Grace Sheehan, Matthew J. Church, Anna P. M. Michel, S. Adam Soule and Timothy M. Shank.

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