How Do Animals in the Deep Ocean Handle the Pressure?
The water on Earth covers approximately 70% of the surface.1 The oceans are a vast body of interconnected waterways with a depth that we still have yet to fully uncover. It might be shocking to know that we have actually only explored about 5% of the oceans and their depths on Earth.2 And as we slowly start exploring the oceans, we learn that there is more and more that we don’t know. In places where we thought there couldn’t be life, life is thriving, almost like its own little world outside of our own. But how does life exist in places with little food and light but plenty of water and pressure?
The oceans are divided in a variety of regions, broadly known as the pelagic (the area where the water is) and the benthic zone (the area along the ocean floor).3 The pelagic zone is then divided into photic and aphotic. The photic zone is the zone where sunlight reaches. It contains everything from the beaches you build sandcastles and surf on, filled with biodiversity, at a maximum of 40m, to as far below as about 200m (the size of about 50 trucks stacked on top of each other).4 In the aphotic zone is the twilight zone at 200m and the midnight zone at 1000m and below.5 The aphotic zone has little to no sunlight, so there are no plants or animals that do photosynthesis in these areas.6 The midnight zone also encompasses the abyssal zone at 4000m (the size of just over 7 CN towers stacked on top of each other) and the trenches at 6000m (the size of almost 11 CN towers stacked on top of each other).7 The deepest area of the ocean is known as the Challenger Deep in the Mariana Trench off the coast of Japan.8
As humans, we are generally in contact with the sunlight zone - where everything is bright and lively. Very few humans have ever gone below this area due to the immense amount of pressure on your body as you dive deeper. At an average depth in the ocean, pressure is more than 380 times higher than it is on the surface. 9 At the deepest trenches of the ocean, it can be more than 1000 times higher than it is on the surface. 10 Even certain submarines cannot go past a few hundred meters!
The reason we have problems diving deeper unless we have really fancy, reinforced submarines is because of the way our bodies are built. Due to the laws of physics, air becomes more compressed as the amount of pressure put on it is increased. 11 Think of those videos you can find on YouTube that show pop cans flattening under the pressure of a hydraulic press. Similarly, marine life that either dive to great depths or live deeper in the water have different adaptations to make sure they can prevent being flattened and crushed like a fly under a fly swatter. Marine life that live in the midnight zone can have liquid filling their body cavities instead of gasses like humans, as liquids cannot be compressed under pressure. 12,13 They may also have unsaturated fats in their cell membrane which act similarly to antifreeze. 14,15 Temperatures deep in the ocean can get quite low, almost 4 degrees Celsius or lower. 16 So, by having liquids in their body that resist freezing, their bodies won’t turn into solids, and therefore, the solids won’t compress and break under the pressure of the water.
So, we know what might happen with the pressure. But if there are no plants that far down the ocean, what do the animals eat?
Depending on the diet of the animal, they can get food from a variety of sources! One of the most common ways to get food at that level is to look around. As you descend lower and lower, you can start seeing what appears to be snow. And not your traditional white fluffy snowperson making snow, but instead marine snow. 17 This is detritus, which is made up of dead and decaying plant or animal matter, pretty much anything organic, including sand and sediment matter from the upper zones of the ocean. 18 Animals in the lower regions of the ocean can eat this. They can also eat from the carcasses of dead animals that end up floating down the water to settle on the ocean floor. 19 They can eat the other animals in the same zone, too! Animals can also gain energy by converting the energy and nutrients that are released from underwater hydrothermal vents. 20 A lot of animals will use bioluminescence (the light that is made by an animal and emitted around them, similar to how a firefly creates its light) to attract other animals right into their mouth. 21
We may not see the animals in this zone often and when we do see them on videos and film, they may seem scary. But due to where they live, the way they look is the most energy conservative way of living for them. 22 The animals in these zones are vital to our climate and regulating carbon sequestering so it is important that we get the chance to learn more about them and help with ocean conservation! 23
Tang, Wei, Bao Dong Chen, and Zhong Lin Wang. “Recent Progress in Power Generation from Water/Liquid Droplet Interaction with Solid Surfaces.” Advanced Functional Materials 29, no. 41 (2019). https://doi.org/10.1002/adfm.201901069.
Widyaningrum, Shinta, Mochamad Subhan Alkyana, and Evvy Kartini. “Indonesia Strategy to Reduce Land-Based Sources Pollution to Achieve the SDG Target on Life below Water.” THE INTERNATIONAL CONFERENCE ON ADVANCED MATERIAL AND TECHNOLOGY (ICAMT) 2021, November 14, 2022. https://doi.org/10.1063/5.0122604.
Webb, Paul. “1.3 Marine Provinces.” Introduction to Oceanography. Accessed November 11, 2023. https://rwu.pressbooks.pub/webboceanography/chapter/1-3-marine-provinces/#:~:text=The%20first%20major%20distinction%20is,are%20known%20as%20the%20benthos%20.
Webb, “Marine Provinces”.
Webb, “Marine Provinces”.
Webb, “Marine Provinces”.
Webb, “Marine Provinces”.
Nakanishi, Masao, and Jun Hashimoto. “A Precise Bathymetric Map of the World’s Deepest Seafloor, Challenger Deep in the Mariana Trench.” Marine Geophysical Research 32, no. 4 (2011): 455–63. https://doi.org/10.1007/s11001-011-9134-0.
“Why Is Pressure Different in the Ocean?” Woods Hole Oceanographic Institution, July 24, 2023. https://www.whoi.edu/know-your-ocean/did-you-know/why-is-pressure-different-in-the-ocean/#:~:text=At%20the%20average%20ocean%20depth,and%20other%20air%2Dbreathing%20animals.
“Why Is Pressure Different in the Ocean?”.
Webb, Paul. “6.1 Pressure.” Introduction to Oceanography. Accessed November 11, 2023. https://rwu.pressbooks.pub/webboceanography/chapter/6-1-pressure/.
Sanderson, Katharine. “Scientists Achieve the Tricky Task of Compressing Liquids.” Nature, 2023. https://doi.org/10.1038/d41586-023-03032-3.
Milsom, William K. “Central Control of Air Breathing in Fishes.” Acta Histochemica 120, no. 7 (September 27, 2023): 691–700. https://doi.org/10.1016/j.acthis.2018.08.014.
Sanderson, “Compressing Liquids”.
Milson, “Air Breathing in Fishes:.
“Why Is Pressure Different in the Ocean?”.
Iversen, Morten H., and Richard S. Lampitt. “Size Does Not Matter after All: No Evidence for a Size-Sinking Relationship for Marine Snow.” Progress in Oceanography 189 (October 19, 2020): 102445. https://doi.org/10.1016/j.pocean.2020.102445.
Iversen, “Marine Snow”.
Iversen, “Marine Snow”.
Iversen, “Marine Snow”.
Iversen, “Marine Snow”.
McClain, Craig R., Andrew P. Allen, Derek P. Tittensor, and Michael A. Rex. “Energetics of Life on the Deep Seafloor.” Proceedings of the National Academy of Sciences 109, no. 38 (2012): 15366–71. https://doi.org/10.1073/pnas.1208976109.
The Ocean Twilight Zone: Earth’s Final Frontier. YouTube. YouTube, 2020. https://www.youtube.com/watch?v=Fma6MM359Z0&t=51s&ab_channel=WoodsHoleOceanographicInstitution.