How Deep-Sea Comb Jellies Hold Their Shape Under Crushing Pressure

For us land-dwellers, being crushed under several miles of ocean water wouldn’t end very well. But for a deep-sea dwelling ctenophore, also known as a comb jelly, being brought up to the surface can be just as bad­.

Scientists working with comb jellies have witnessed this firsthand—taken from their deep-sea environments, the ctenophores seemingly “melt” in the lab, losing their shape and essentially disintegrating. Now, a new study published last week in Science tackles the mystery of why this happens, revealing how these creatures’ cells are specifically tuned to the depths where they live.

“For some deep-sea ctenophores, their cell membranes are literally held together by pressure,” Jacob Winnikoff, a deep-sea biochemist at Harvard University and the study’s lead author, tells Scientific American’s Elizabeth Anne Brown.

Ctenophores are predatory sea creatures that live at widely varying depths across the world’s oceans. Despite their name and translucent appearance, comb jellies aren’t closely related to jellyfish. They use rows of threadlike cilia, known as combs, to propel their soft bodies through the water in search of prey. And, according to the study authors, understanding how their cells work could hold important lessons for human health.

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The new research is “a seminal contribution to understanding life in high-pressure environments,” Douglas Bartlett, a deep-sea microbiologist at the University of California San Diego who was not involved with the study, tells Science’s Sean Cummings. “It’s a totally new way to think about adaptation to the deep sea.”

To learn more about how ctenophores can live at different depths—and to untangle the impact of pressure on their bodies—the researchers collected different species of comb jellies from a range of sites across the Northern Hemisphere.

They tried to collect specimens from similarly cold-water places, varying only the pressure the animals are typically exposed to. In low-pressure locations, like in shallow Arctic waters, scuba divers could pick up the creatures. In deeper, high-pressure waters, some 2.5 miles beneath the sea surface off California’s coast, the team used remotely operated vehicles to carefully vacuum up specimens, per Scientific American.

Scientists then analyzed the ctenophore tissues they’d collected, looking specifically at the shapes of lipids, or fats, that make up cell walls.

In general, cell walls need to be firm enough to hold the cell together, but flexible enough to let proteins inside move around and maintain the cell’s functions. To accomplish this delicate balance, the lipids need a particular pattern of cylindrical and cone-shaped structures.

The research revealed that the shape of these structures in a comb jelly differs depending on where its species is adapted to live. And deep-water ctenophores are a particularly dramatic case: Their lipids form especially exaggerated cone shapes.

With the pressure of miles of ocean above them, these cell walls are held in a workable shape. But when the deep-sea comb jellies aren’t under extreme pressure, such as when scientists bring them to the surface, the lipids expand into those exaggerated cones, curving into a flimsy shape that leads the cell walls to fall apart.

The highly flared structures found in the new study belong to a class of lipids called plasmalogens. To confirm that these structures help comb jellies live at crushing depths, the researchers created E. coli bacteria that made their cell walls with the plasmalogens found in deep-sea comb jellies. They then grew those bioengineered bacteria at pressures equivalent to those roughly 3.1 miles under the ocean surface—where normal E. coli can’t survive. But the modified bacteria thrived, according to a statement from the University of California San Diego.

These findings could help future researchers learn more about human cells. Plasmalogens are not just found in ctenophores—they’re also common in human brain cells, and research indicates that declining abundance of these lipids corresponds to neurodegenerative diseases such as Alzheimer’s. Revealing the structure of plasmalogens could help scientists understand this link and even look for new treatments for neurodegenerative conditions.

“I think the research shows that plasmalogens have really unique biophysical properties,” Itay Budin, a biochemist at the University of California San Diego and a co-author of the study, says in the statement. “So now the question is, how are those properties important for the function of our own cells? I think that’s one takeaway message.”

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Rudy Molinek is Smithsonian magazine's 2024 AAAS Mass Media Fellow.