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How Do Deep Sea Creatures Survive? (A Mystery Reveled)

The ocean is filled with life. You can see the life in the ocean for yourself by stepping into the beach. It’s the shallow end of the ocean. What about the deep end of the ocean? Do life exists in that deep end of the ocean and how do deep sea creatures survive ? Those are the common questions asked when talking about deep sea creatures. So let me answer you clearly in this super interesting article. Lets’s dive in.

How Do Deep sea Creatures Survive

How do deep-sea creatures survive?

Deep sea creatures are the animals that live below the “photic zone” of the ocean. The photic zone is the top layer of the ocean that receives sunlight. Sunlight allows phytoplankton to perform photosynthesis and produce food. Generally, the animals that live below this zone cannot get preferable conditions to live in. These animals must survive in extremely harsh conditions, such as immense pressure, small amounts of oxygen, very little food, no sunlight, and constant, extreme cold. Most creatures have to depend on food floating down from above as there is no productivity.

But the interesting thing is, there are some creatures that live hundreds or even thousands of meters deep in the ocean and have adapted to the high pressure, lack of light, and other factors. Examples of deep-sea creatures are sharks, whales, seals, crabs, Atlantic Wolffish, sea urchins, fangtooth fish, giant tube worms, vampire squids, Pacific Viperfish, anglers, red-lipped batfish, dumbo octopus, hairy frogfish, coffin fish, spotted handfish, giant isopods, Atlantic footballfish, zombie worms, and many others. Mariana snailfish (Pseudoliparis swirei) is considered the deepest sea animal that thrives at depths of up to about 8,000 meters (26,200 feet) along the Mariana Trench near Guam.

Many of the deep sea creatures look weird. This is because they adapt to the harsh conditions in the deep ocean. 

How do deep-sea creatures survive the pressure (adaptation)

The water pressure in the deep sea is several hundred higher than normal pressure and it is a real challenge to live in the deep sea. Ideally, high pressure in the deep sea should crash us! But, the incredible fact is that many marine species survive even at the highest possible pressure found as deep as 25,000 feet below the sea surface. Then how do they thrive in the deep sea below thousands of feet?

This is because, these creatures have several adaptations like compressible lungs, lung-like swim bladders, etc., to help them overcome the high water pressure in their deep-water environment. Before diving into the water, many deep-sea creatures exhale nearly 90% of the air in their lungs and keep only around10% of the oxygen available for their use. The survival of marine creatures in less oxygen supply is made possible by several factors. Some of them are listed below. 

Lowered Metabolic Activity

Under high pressure, some deep-sea creatures such as whales and seals shut down their digestion, liver, and kidney functions. Although not considered deep-sea animals, Penguins basically shut down all their organs except for their heart and their brain when doing deep dives.

Absence of Swim Bladders

The absence of Swim bladders is another clever adaptation of deep sea creatures. Basically swim bladders are bad for an animal under pressure., so most deep-sea animals avoid having them. While the creatures living in the deep sea lack swim bladders, deep sea divers like whales and seals have collapsible lungs to deal with extreme pressure.

Presence Of Trimethylamine Oxide (TMAO)

One of the challenges that deep ocean fish face is to keep the proteins and other vital molecules undistorted under high pressure. The high pressures can break down proteins, which are important for normal physiological processes. For that, they have a special formula, called Trimethylamine Oxide (TMAO). It prevents the distortion and compression of vital molecules within the body under intense external pressure. Most animals have one copy of these genes, while these creatures have more than one. The deepest living creature Mariana snailfish has five of them.

Further, pressure can even make molecules more or less toxic. For example, urea becomes more toxic as the pressure increases. So deep-sea sharks, which like all sharks have a lot of urea in their blood, also have a lot more protective chemical TMAO to offset this effect than do their shallow water cousins.

No Nitrogen Absorption

The divers sometimes get nitrogen narcosis, due to breathing compressed inert gasses at high pressure. The secret to why those animals do not get nitrogen narcosis and decompression sickness is they have adapted to have less nitrogen absorption. 

Adaptations of body structure 

According to a Chinese research team, the deepest living creature, Mariana snailfish, has a few peculiarities that help it thrive under high pressure. One such adaptation is that the fish have gaps in their skulls. It helps the internal and external pressures to be balanced. In another word, if this fish has a fused skull like humans or other land-living creatures, it would be crushed by the pressure. This adaptation helps to balance the pressure. 

Another adaptation of their anatomy is that their bones are not entirely made of, well, bone—but are largely cartilage. In fact, the fish have a mutation in the primary gene responsible for calcification. If calcification happens, their bones may build up calcium and it would harden their bones. This mutation renders the gene partially nonfunctional. This makes their bones more flexible and likely more able to withstand pressure.

As you may remember from high school or college biology, a cellular membrane consists of the lipid bilayer. The structure is entirely maintained by the interaction of charges (or lack of) between water and the phospholipids. Extreme pressure results in a tighter packing of the phospholipids which lowers the permeability of the membrane. Another adaptation by deep-sea animals to increase cellular permeability is to increase the percentage of unsaturated fatty acids.

At the basic level, pressures would also select for different enzymes. Changes in protein structure can influence their cellular function as mentioned before. Proteins contain hydrogen and disulfide bonds between different subunits and parts of the amino acid chain that both dictate structure. A selection for proteins with increased bonding would minimize changes in shape to do pressure.

How Do Deep sea Creatures Survive

How do deep-sea creatures survive without sunlight?

Obviously, sunlight is one of the major factors of life on earth. It is the energy source of photosynthesis. And also it is the primary light source of many organisms. However, there is no or little sunlight penetrating the deep sea area. So how do they produce food without sunlight? It’s simple they invent a new way to produce food. The process they use to create food is called chemosynthesis (not photosynthesis). Chemosynthesis is the process by which certain microbes create energy through a chemical reaction. It transforms one or more carbon-containing molecules and nutrients into food using different energy sources than sunlight. Especially the animals that live around underwater volcanos make their living from the chemicals coming out of the volcanos. 

The deep sea creatures overcome the problem of lack of sunlight by creating their own light source! This self-producing light is known as bioluminescence. All deep-sea animals do not have bioluminescence, but most have. Even though it is dark down there, most deep sea fish have eyes. This makes it easier for them to pick up bioluminescent light and residual sunlight. Bioluminescence is the result of a chemical reaction that allows living organisms to produce light. About 90% of creatures in the deep sea are capable of bioluminescence. They use bioluminescence to accomplish different functions which are listed below. 


Some species like black dragonfish generate this light to use headlights while some (humpback anglerfish) use the same as a lure to attract prey. 


Another common use of bioluminescence is communication. This is very useful to find their mates.


It can also serve as a defense tool. Some animals, in areas with dim light, make themselves luminescent to camouflage themselves in the light. Some deep-sea squid drops a bioluminescent cloud and make their escape instead of releasing the ink. 

Further, dragonfish can produce bioluminescent blue light like other deep sea fish whilst they are also capable of far-red light, using photophores in their eyes. Since there’s little to no red light available in the deep ocean, most creatures there aren’t receptive to it. This lets dragonfish light up their prey without their prey seeing the light.

How do deep sea creatures survive the cold

As there is no sunlight penetrating the deep sea, the water in the deep sea area is very cold. While the average temperature of the deep sea (500-1000 ft) is 4 0C, the temperature at 1000- 3000 feet ranges from 1 to 4 centigrades. The coldest area in the ocean is the deep-antarctic ocean in which the temperature is around -20C. Despite the extreme conditions in the deep ocean, they are still teeming with life. The deep sea animals have adaptations to survive cold. The small planktonic copepods, a species of crustacean that lives in Antarctica’s waters, have 70% body fat, making them one of the fattest organisms in the world. This fat gives them an energy reserve that they can tap into when food becomes scarce across the unpredictable seasons of Antarctica. Caviars beaked whale has a nearly 6 inches blubber layer found under the skin.

You may think, with the low temperature, thee creatures may die by freezing. It will not happen as they have special anti-freeze proteins. These proteins circulate in the fish’s blood and bind to any ice crystals that begin to grow, preventing them from growing any further.

How do deep sea creatures survive without oxygen?

Oxygen concentration in the deep sea area is low and limited. The adaptations to a low oxygen environment differ from one to another depending on the taxa they belong. Before diving into the water, deep-sea mammals exhale nearly 90% of the air in their lungs and keep only around10% of the oxygen available for their use. The survival of marine creatures in less oxygen supply is made possible by several factors. Some of them are listed below.

Holding the breath for hours 

Actually, most of these creatures, especially mammals, do not spend the whole of their lives in the deep ocean. They come to the ocean surface from time to time to get enough oxygen. This is mainly done by whales and seals. Their ability to be resilient in high-pressure deep-sea waters shocked the world. For example, the Cuvier’s beaked whale can dive as deep as 2,992 meters and withhold its breath in water for a record 2 hours and 18 minutes. Further, the elephant seal can hold its breath in water for 2 hours. 

Completely compressible lungs

This is also related to deep-sea mammals. The beaked whale considers the deepest diving cetacean. According to the reports, the lungs collapse forcing all of the gas in its lungs out into the muscles and bloodstream where the gas is dissolved when it is in the deep sea. Their muscles are well adapted to do it. Their muscles hold more myoglobin, which supplies oxygen to the cells in their muscles.  And also their blood possesses more hemoglobin for the storage of oxygen. Therefore, they can store oxygen more than a land-living mammal. Collapsing of the lungs results in reduced air pockets and minimum oxygen available for its survival.

Lowered heart rate 

The way to utilize low oxygen is to reduce the internal processes. In some creatures, the heart rate is minimized to about 4 beats per minute while others stop breathing for a while when diving into the deep sea.

Reduced Movement

Oxyegn demand is higher when you awaken and are active than you sleep. The same scenario applies here. The deep sea creature is not so active when they are in the deep ocean. They reduce their movement so that they glide rather than swimming downwards. Gliding is a process that requires no muscle movement; saving the creatures’ oxygen for use on their journey back to the water’s surface. 

Adapt to low oxygen concentrations 

Copepods (tiny crustaceans that function like insects of the sea) in the genus Lucicutia have fine-tuned their life cycles to different oxygen levels. L. grandis, a large red-orange species, is common in the most hostile regions of the Arabian Sea. Adults live at the deepest level of the ocean, where the oxygen concentration of about 0.14 milliliter per liter is adequate for reproduction.

No mitochondria

Scientists found a multicellular animal that doesn’t need oxygen at all. It is loriciferance that lives in the deep sea. Instead of mitochondria, which rely on oxygen, the creatures have organelles that resemble hydrogenosomes, which some single-celled organisms use to produce energy-storing molecules anaerobically.

How Do Deep sea Creatures Survive

Can deep sea creatures survive on the surface?

The deep sea creatures adapted to the extremely high pressure in the deep sea. Their body pressure is high as the external water pressure to avoid being crushed by the water pressure. When they come to the surface rapidly, their internal pressure is much greater than the air pressure which can cause their bodies to burst. However, if they get to the surface more slowly, the pressure has a chance to equalize to some extent.

Although, every deep sea creature cannot adjust their internal body pressure to be equal to the air pressure many of them are doing it successfully. They can withstand various ranges of pressure if they move slowly while allowing their bodies to adjust to the external pressure. Some pelagic organisms also have amazing vertical migrations during the course of 24 hours that can encompass 1000’s meters and many levels of pressure. However, they cannot withstand the low pressure on the surface for a long time. 

The temperature difference also makes it the deep sea creatures hard to survive near the surface. They adapted to cold temperatures and it is nearly impossible for them to adjust to the high temperature near the surface. 

Therefore, in conclusion, the extrema difference in pressure and the temperature between the sea floor and the surface makes the creature’s survival on the surface near impossible. Unfortunately,  this makes in-depth research difficult because most useful information can only be found while the creatures are alive.

What do deep sea creatures eat?

It is not only the pressure, temperature and light that are the extreme conditions in the deep ocean. Even foods are scarce resources in the deep ocean. All the deep sea creatures are carnivores as there are no plants in the deep sea. In the absence of sunlight, most animals in the deep ocean (below 200 m) depend on detritus from the surface waters as their primary source of food. This is commonly known as “marine snow” and is mainly composed of dead plankton and fecal pellets produced by zooplankton, which are exported to the deep seafloor as fine particles. 

Besides, they scavenge animals that sink to the seafloor when they die, sometimes called “whale falls”. They colonize near a caracas and stay there until they eat up the whole caracas. The skeleton host chemoautotrophic fauna and they thrive off hydrogen sulphide generated by the anaerobic decomposition of skeletal lipid.

However, they don’t get enough food all the time. For example, animal caracass hardly sinks to the bottom. Therefore, some the animals like crabs have special adaptations to eat a large portion of food at a time and store it for periods when there is no food. Those carbs can store the foods in their stomach for a week or longer. Further, their metabolism is slower than the land-based or surface-based animals which allows them to thrive with littleamount of food. 

how do deep-sea creatures see

Sight is essential for most animals for seeking food, finding mates, and spotting predators. So when the light gets low, nature gets creative. A few of the adaptations of the deep sea animals to see in minimal light are as below.

Looking Up

Some deep-sea predators swim just deep enough to make it hard for their prey to see them. For example, Pacific barreleye has directly upward eyes and they see the shapes of their prey while hiding in the dark waters. Then they can rotate the eyes forward as they line up to attack. They hide in the darkness and appear, as if out of nowhere to attack their prey. Then they disappear into the cover of darkness. 

The pocket shark also uses a similar tactic. They swim deep enough to keep out of sight of their prey.  Instead of coming up to attack, they lure their prey down. Then it shoots bioluminescent goo in front of itself, and when prey comes down to investigate, they gobble them up.  

Mirrors in the Eyes

This adaptation is used by the nocturnal land-based animals also. Owls especially have a mirror-like layer behind the retina instead of lenses. This allows them to get more out of less light. Scallops have one of the most complex image processing systems out there. They use a network of 200 eyes with concave mirrors made out of guanine crystals.

Guanine is a naturally occurring super-reflective material. It’s found in shiny fish scales and chameleon skin. It prevents optical distortions while maximizing the use of light. This allows scallops to see even in low light conditions.

Big Eyes

Although there are plenty of examples of deep water gigantism, the vast majority of creatures here are getting smaller. There’s less food, and the extreme cold and pressure take up more resources to hunt and process meals. However, their eyes are big compared to their body size. Enough Light condition is essential to see things. As deep sea creatures don’t get enough light their way is to evolve bigger. The stout blacksmelt is such a fish and found as deep as 6600 m. As they get little light, to cope with the threat condition, they have huge eyes with lots of cones, allowing them to make the most out of the light available.

Credit to : Natural World Facts

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About Dr.Chamika

Hello, I'm Dr. Chamika. I am a Researcher in Water quality, Aquatic organisms, and Environmental chemistry. I am a passionate fish keeper, with10 years of experience. My mission is to help other aquarists experience the joy of fish keeping.