Question: How do deep-sea organisms survive under so much pressure?

Answer: The staggering pressure in the deep sea would crush most life that we’re familiar with. The organisms that live there have a series of fascinating adaptations that make life there possible.

As scuba divers know well, pressure increases with depth. Standing on the surface at sea level, you experience one atmosphere of pressure, which is about 15 pounds per square inch (PSI). For every 33 feet (10 meters) that you descend under the water, another atmosphere of pressure is added. Most divers never go below 100 feet (30 meters) or so, but marine life can be found much, much, much deeper than that. The Psuedoliparis snailfish, for example, was discovered deeper than 8,000 meters.

Pressures at that depth would obliterate life as we know it. “Pressure in the deep sea is up to 1,000 times higher than what we experience at the surface, the equivalent of an elephant standing on your thumb,” explains Dr. Mackenzie Gerringer, an associate professor of biology at State University of New York Geneseo. “People think that this means that deep-sea organisms need to be very strong, like a titanium submarine. But water pressure actually pushes on organisms from all directions, not just above. You feel this when you go in the water, the water doesn’t just feel like it’s pushing on us from above, we feel the squeeze from all around.”

This means that adapting to life in the deep requires a wide variety of adaptations. “Many deep-sea organisms have adapted to limit air spaces in their body because air is so compressible,” Dr. Gerringer tells me. Instead of a gas-filled swim bladder like those used by shallow-water fish, many deep-sea organisms use a fatty liver, extremely low-density bones, or gelatinous tissues to help them stay neutrally buoyant. “This is why many deep-sea fishes are gooey looking. My favorite example is the blobfish, which has a lot of gelatinous tissues under their skin, making them look blobby when they are taken out of the water!”

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These adaptations don’t just take place at the level of organs and tissues, but at the cellular level! “High pressures impact cell membranes, making them solidify, like butter in the refrigerator,” Dr. Gerringer says. “A healthy cell membrane needs to be able to move enough for the cell to operate, but not so much that it falls apart. Deep sea organisms have specialized membrane structures to keep their cell membranes moving under high pressure. And sometimes, deep-adapted species will accumulate specialized compounds that help keep proteins working under high pressure. One of these molecules is called Trimethylamine N-oxide, or TMAO. While you might not be familiar with TMAO, you know the smell, it’s what gives the ‘fishy’ smell of fish.”

The deep sea is a fascinating ecosystem, and it’s incredible that life can survive there at all—scientists did not know life was possible until recently. “These high pressures that are characteristic of deep-sea habitats have led to a remarkable array of adaptations across the tree of life,” Dr. Gerringer continues. “Although we’ve continued to learn about these adaptations, there is still much more to be discovered about the incredible organisms with whom we share our planet.”

Ask a Marine Biologist is a monthly column where Dr. David Shiffman answers your questions about the underwater world. Topics are chosen from reader-submitted queries as well as data from common internet searches. If you have a question you’d like answered in a future Ask a Marine Biologist column, or if you have a question about the answer given in this column, email Shiffman at [email protected] with subject line “Ask a marine biologist.”

Dr. David Shiffman is a marine conservation biologist specializing in the ecology and conservation of sharks. An award-winning public science educator, David has spoken to thousands of people around the world about marine biology and conservation and has bylines with the Washington Post, Scientific American, New Scientist, Gizmodo and more. Follow him on @WhySharksMatter on Twitter, Facebook and Instagram, where he’s always happy to answer any questions about sharks.

The views expressed in this article are those of David Shiffman, and not necessarily the views Scuba Diving magazine.