New UM Bio Station Study Finds Unlikely Food Source for Deep Sea Crustacean

Could a deep-sea crustacean play an important role in the future of our changing planet? In a new study published in the journal Proceedings of the Royal Society B: Biological Sciences, Flathead Lake Biological Station postdoctoral research associate Logan Peoples and a team of scientists found that a remarkable isopod species named Bathyopsurus nybelini has adapted to feed on an unexpected food source—sunken algae known as Sargassum.

“Many might think of deep-ocean organisms as strange, weird, or otherworldly,” said Peoples, a co-lead author on the study. “When we watch this organism swim while carrying macroalgae, the only thing that comes to mind is how beautiful and graceful it is.”

Peoples and his fellow scientists—which include researchers from the Woods Hole Oceanographic Institution (WHOI), the University of Montana’s Flathead Lake Biological Station (FLBS), State University of New York (SUNY) Geneseo, Willamette University, and the University of Rhode Island—were able to demonstrate that the isopod is specially adapted to find and feed on this sunken source of nutrients.

These findings of a deep-ocean animal relying on sinking food from waters miles above prove how closely connected the surface ocean is to the deep ocean.

“This isopod, that appears to lack eyes, is finding, carrying, and eating algae that sunk from the surface at depths three times deeper than Logan Pass in Glacier Park is tall,” Peoples said. “It highlights how the deep ocean is not that far removed from the surface.”

Sargassum grows at the ocean’s surface, forming floating forests of photosynthetic algae. During storms, Sargassum sinks to the seafloor where it has significant implications for carbon cycling and storage. It also serves as a food source for isopods like the Bathyopsurus nybelini.

Using WHOI’s submersible Alvin, on the first cruise since it’s upgrade to reach depths deeper than 18,000 ft, the scientists encountered this isopod swimming 3.7 miles deep in the Puerto Rico Trench, the boundary between the Caribbean Sea and the Atlantic Ocean, and the Cayman Trench, the deepest part the Caribbean Sea near Jamaica. The isopod swims backwards and upside down, with oar-like legs as long as your fingers. It is expertly adapted to feeding on sunken algae, with serrated and grinding mouthparts that are ideal for tearing and gut bacteria that aid digestion.

Algae like Sargassum are difficult for many animals to digest because the cell walls are built of strong, complex molecules called polysaccharides. But the gut microbiome of the Bathyopsurus nybelini has genes that break down these tough compounds. As found in the human gut, the microbiome provides access to important carbon and nitrogen nutrients for these hosts.

SUNY Geneseo undergraduate researcher Abisage Sekarore analyzed video of the seafloor in the Puerto Rico and Cayman Trenches collected by the submersible Alvin, identifying hundreds of Sargassum fronds.

"Far more Sargassum was observed and recorded in the deep ocean than anticipated, with deposits found on the seafloor at depths greater than 6,000 meters,” said Sekarore. “In just one dive, over 300 deposits were recorded, raising questions about the connection between the surface and Sargassum as a potential food source for the isopods."

The abundance and distribution of Sargassum in the tropical Atlantic and Caribbean Sea appears to be changing, with large blooms creating ecological and economic impacts for coastal communities in the region.

Further studies will need to evaluate how much and where Sargassum arrives at the seafloor, how the algae's sinking changes over seasonal and long-term timescales, and connections to the broader deep-ocean food web.

Understanding the ecological impact of altered Sargassum deposition will be crucial for predicting the responses of deep-ocean communities to changing environmental conditions and for developing strategies to mitigate these impacts.

“Deep-ocean ecosystems seem like harsh environments, but the animals living in these habitats are well-suited to meet these conditions,” said study co-lead author Mackenzie Gerringer, a deep-ocean physiologist at SUNY Geneseo. “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. We’re excited to share its amazing story of adaptation and this important reminder that habitats and organisms on our planet are deeply and intricately connected.”

Funding for this work was provided by the National Science Foundation, Simons Collaboration on Ocean Processes and Ecology, the State University of New York at Geneseo, and the Woods Hole Oceanographic Institution.

For the complete study, visit the Proceedings of the Royal Society B: Biological Sciences website at https://royalsocietypublishing.org/doi/10.1098/rspb.2024.0823

(Adapted from a release by the Woods Hole Oceanographic Institution)

Banner Photo: An isopod swims backward and upside down in the deep ocean using large paddle legs, carrying Sargassum algae that has sunk from the surface miles above. (Photo Credit: L. Peoples (UMT), NDSF Alvin Group, NSF, ©Woods Hole Oceanographic Institution)