The ocean holds a great assortment of mysteries and fascinating creatures that push the boundaries of both physics and chemistry. One such phenomenon is that of those sea creatures that dwell at extreme depths under the water. As humans, we barely feel the 14.7 pounds of pressure, also known as gravity, that keep us firmly attached to the ground. Ocean water, on the other hand, is composed of different materials and has a pressure of its own due to its density. As you dive underwater pressure increases by the equivalent of one atmosphere for every 10 meters, or 33 feet. The deeper you go, the more extreme the pressure build up and the more damage will be inflicted upon the human body due its composition of mostly water. For humans, at 100 meters underwater, we experience one atm of air pressure and 10 atm of water pressure, for a total of 11 atm (NOAA). This is why deep sea diving for humans is extremely dangerous and difficult. Deep-sea dwelling creatures, on the other hand, are able to not only survive but also thrive and grow at extremely deep expanses.
While humans need oxygen in their lungs to survive, deep diving mammals, such as whales and seals do not seem to encounter the same need as we do. In fact, these mammals let their lungs collapse completely as they dive deeper and deeper. How can they do this and still survive? Their secret is to store oxygen in their muscles, allowing it to be absorbed through their blood starting in the muscles, instead of breathed through their lungs (Kunzig). This is successful because these sea dwelling mammals’ muscle tissue contains much higher concentrations of oxygen-binding myoglobin than a human does (Kunzig). Additionally, as the lungs are collapsed, they become heavier, allowing, for example, seals to sink more quickly and use less of their stored oxygen on their descent. However, just because these mammals have this capability, does not mean that they spend the majority of their time, or dwell, at extreme depths.
Seen in the image above, only certain creatures can survive and dwell at certain depths. What about aquatic creatures, such as deep dwelling fish? Deep sea fish and creatures have adapted overtime and their cell membranes are composed of thinner, more soggy material than humans. Cell membranes are made of fats that allow proteins, nutrients, waste and other molecules in and out of the cell (Kunzig). High pressure causes these fats to tense up if they are not fluid enough, which is why deep-sea creatures use more unsaturated fats to build their cell walls. Largely, these fish and creatures contain the same metabolic enzymes and humans. However, their enzymes appear to be able to change shape without changing volume and combine in ways ours cannot. Just a couple mutations can create a pressure-resistant enzyme, which is what is keeping these deep-sea creatures alive.
Another obstacle to contend with is the lack of light at extreme depths. How do they see, hunt or swim without running into things? Some creatures have developed large eyes with retinas containing reflective qualities allowing them to multiply any small light source (Lane). Others can sense vibrations of other creatures, or prey, and use the location of the vibrations to hunt and move. Still other creatures produce their own light through structures known as photophores. These photophores emit light in a process known as bioluminescence (Lane). Finally, what do they eat? Because life, and consequently, food, is scarce at extreme depths, many deep-sea creatures wait for the death of a larger creature, such as a whale or dolphin, to sink down to their depth (Lane). This sustains a multitude of extreme depth creatures, however some predatory fish and other creatures hunt one another for food.
Kunzig, Robert. “The Physics of . . . Deep-sea Animals.” Discover Magazine. Discover Magazine, 01 Aug. 2001.
“The Impacts of Pressure at Ocean Depth Are Less for Organisms Lacking Gas-filled Spaces like Lungs or Swim Bladders.” NOAA Ocean Explorer Podcast RSS. National Oceanic and Atmospheric Administration, 14 Feb. 2013.
Lane, Sana. “The Survival Strategies of Deep Sea Creatures.” Fiboni. Themedy, 15 Mar. 2013.