Season 2: Episode 1- The Physiology of the Creatures of Atlantis (Aquaman)

Film: Aquaman (2018)
Production Company: Warner Bros. Pictures
Distributed By: Warner Bros. Pictures
Monster: Karathen/Sea-Dragon-Horse
Featuring: Sam, Adam, David
Rating: Mature (for some offensive language and adult themes)



The world of Aquaman is full of a variety of different organisms. We could spend days discussing all of the different life forms. However, for our purposes we decided to focus on two very different creatures, the Karathen and the Seahorse/Sea Dragon mounts.

The Karathen


The Karathen is the feared guardian of the King Atlan’s Trident. It is believed to be one of the oldest and most powerful creatures on the planet. Within the film, the creature is discovered behind a waterfall in the Hidden sea, protecting the Trident of Atlantis from false claimants. The creature is enormous both in height and general mass, looking to be the size of a small skyscraper. It is covered in thick dermal plates, has enormous jaws, 6 long appendages similar to a crab, and a mass of tentacles arising from the caudal most aspect. Within the film the creature is voiced by Julie Andrews.

The Karathen has a number of interesting physiological principles to explore, as covered below.

Size, Respiration and Metabolic Constraints

As we have discussed in previous episodes, there are rules governing how large terrestrial organisms can get. We discussed that King Kong would have serious issues with topics ranging from respiration, to heart function, to general mobility. Being bigger when on land leads to increasing difficulties with forces like gravity weighing down on you.

However in the water, the rules are different. You are still experiencing the effects of gravity when in the water, but it is not directed in the same way. The square cube law still applies but your mass is displaced by the water and buoyancy becomes the most important force. As a result, aquatic animals can be much larger than anything typically seen on land. Stranger still, it appears that in some cases creatures get bigger as you move deeper into the ocean, a phenomenon we still don’t fully understand. Creatures like the giant squid are one example. Some theories suggest that since the creatures don’t have to expend energy regulating body temperature at depth and have a smaller need for activity, they can allocate more resources to bodily processes. However, this is just a theory.

The Karathen would likely have an exoskeleton, similar to what is seen within a crab or lobster. Based on its’ extreme size and some of the demanding activities we see it take on in the film, it would likely have very high metabolic demands. This would create difficulties with oxygen extraction. Normal air contains approximately 21% oxygen and provides sufficient metabolic fuel for most terrestrial organisms. However, the dissolved oxygen in the water is typically less than 1%. As a result, most aquatic life has limits on the level of activity that can be performed. The Karathen might be able to survive at depth and be as big as it is, but it would not be the fast moving creature that the film portrays it as.

Moving a large body through water is incredibly taxing, especially with very long limbs that are not particularly hydrodynamic in design. If you have ever watched a cra slowly moving along the ocean floor, you have an understanding of how this might work. The fast movement associated with the tentacles and claws could not occur. Furthermore, the massive strength behind the swings that knocks creatures flying in every direction would not be possible.

In order to meet even basic energy demands for movements and survival, the Karathen must be consuming some high caloric material. It is not clear what food sources might be available in the area that the Karathen guards, but it will not be able to survive only on wannabe trident seekers. We can’t rule out the possibility that she has also been feeding on The Trench.

Pressure Tolerance/Carapace

Surviving at lower depths requires physiological modifications to survive high pressures. If you have ever dived into the water and tried to swim downwards before, you have likely felt some discomfort in your head and ears. When on land, the air around you exerts pressure on your whole body as a result of forces like gravity. We measure this pressure we use units like pressure per square inch (psi), bars, or or atmospheres. When standing at sea level you are experiencing 1 atmosphere of pressure. However, when descending into the ocean, the deeper you go under the sea, the greater the pressure of the water pushing down on you. For approximately every 10 meters) you go down, the pressure increases by approximately 1 atmosphere or 14.5 psi. Animals surviving at deeper ocean depths have evolved mechanisms to help allow them to function under increased pressure.

The mechanisms that are typically utilized for survival at depth are

  1. Removal of small cavities that would collapse under pressure
  2. Removal of air/replacement with water where possible (water is incompressible)
  3. Biochemical changes to resist pressure on the cellular level (ex: TMAO)

It is likely that the Karathen would employ a few of these changes to better protect itself at depth. However, the important feature to understand that changes in physiology to pressure would likely restrict the Karathen to survival to a limited range within those depths. Although it is true that some species of aquatic mammals like dolphins or whales can descend to increased depths and then return to the surface, it is important to remember that this is a temporary action. Most deep sea living species adapt to extreme pressure and cannot be brought to the surface without dying. Multiple attempts have been made to capture live deep sea species and most have led to the death of the organism. If you adapt to live under extreme pressure then absence of that pressure is typically fatal. The Karathen would not be able to move to the surface as seen within the film.


Within the film, the Karathen is seen to telepathically communicate with Aquaman. Although there are multiple seen where Aquaman is seen to be signalling and seemingly commanding other aquatic life, this is the first time he is seen actively talking with anything.

In order to discuss the Karathen to Aquaman communication, we must first address the Aquaman to Sea Life communication. There are multiple mechanisms for communication between biological systems in nature. The primary mechanism that I feel could be employed by aquaman for communication with aquatic life would be:

1] Pheromones

Multiple aquatic species communicate through the water using pheromones. Good examples are the sex pheromones in Sea Lampreys (Petromyzon marinus) and Shore Crabs (Carcinus maenas). However, I don’t think this is how Aquaman is communicating. Firstly, pheromone communication is very slow and difficult to direct towards one particular animal. Secondly, in the film we clearly see a young Aquaman communicating with fish at the aquarium through a chunk of plate glass. This would not be possible with pheromones.

2] Electric Signalling

Many types of aquatic life use electrical currents for communication and tracking. Many forms of sea life like sharks, lungfish, and aquatic salamanders have a specialized electroreceptive organ called the Ampullae of Lorenzini that they use for detecting electrical signals. Electroreception has been observed almost exclusively in aquatic or amphibious animals as water is a much better electrical conductor than air. Weakly electric animals can communicate by modulating the electrical waveform they naturally generate, a mechanism that is primarily used for mate attraction and territorial displays. Aquaman could theoretically harness this mechanism to communicate with a wide variety of fish. However, specific instructions would be difficult to communicate. Also, there would be limitations as to which fish types would be able to receive the communications and have their behaviours altered accordingly.

3] Sonar/Ultrasound Communication [most likely mechanism]

Among the different mechanisms for communicating in an aquatic environment, sound is the most effective and most likely mechanism that Aquaman would harness. Sound waves travel rapidly underwater (~1,500 m/s) and water serves as a much better conduction medium than air. Fish send and receive sound cues underwater using similar, but different mechanisms to life on land. Fish have an ear of sorts but use something called otoliths or ear stones to transmit mechanical disturbances of the water into neurological signals interpreted by the brain as sound. Fish can generate sound/noises underwater to be heard by others, but usually communicate in clicks and hear best within a lower frequency (30-1000 Hz) than terrestrial organisms underwater (400-2,000 Hz). The sounds produce are generally used for communication related to reproduction or stress and can be used over very long distances.

Sonar is the mechanism that makes the most sense for Aquaman to be utilizing within the film. If he could modulate the sound waves that he is putting out from a specialized organ (in his hand, face, etc) to generate different frequencies to replicated attraction/stress signals he could theoretically summon and scare aquatic species into defending him. Although it should be noted that he would not be capable of some of the very intricate commands he seems to be able to give out in the film. This mechanism would explain why when aquaman uses his powers there seems to be a ripple effect generated from his hand at the aquarium.

In regards to the Karathen though, the mechanism of communication might be a little different. The Karathen does not seem to be commanded by Aquaman, it seems to be actively communicating with him. In order to do this they would need to be speaking underwater. The Karathen goes out of her way to explain that no Atlantean has be able to communicate with her since King Atlan. This would suggest that Aquaman possess some unique characteristic. The simplest explanation would be that Aquaman is capable of hearing and communicating at a frequency below that of normal Atlanteans. As discussed, typically fish communicate in water between 30-1000 Hz, while terrestrial organisms underwater communicate at 400-2,000 Hz. If the Karathen normally communicates at a frequency that only King Atlan and Aquaman can hear at, that might explain why no one else has been able to carry on a conversation.

Enormous Sea Dragon/Seahorse


Throughout the film, and featured most prominently in the final conflict of the film, various characters can be seen riding on some Sea Dragon/Seahorse hybrid. Within the early comics and some of the early animated films, Aquaman was often seen riding an oversized white seahorse named Storm. It is assumed that the version within the film was a modernized take.

The adapted “Sea Dragon” seen within the Aquaman film is a large, aquatic, scaled creatures with a variety of body frills/fins, no arms, and two long legs originating from the hips and ending in unconventionally designed webbed feet. The creatures body plan looks like an enlarged Seahorse, not a Sea Dragon, with a curled tail, lack of front limbs, and an inverted thorax. As a results, most of our calculations and discussions will be done in context of this appearance. There are a number of major issues associated with is creature and how it moves, acts, and would work in the real world.

Size & Metabolism

A seahorse has a respiration system that is based on properties of passive transport. Seahorse gills are different from most other fish in that they are tufted. Tufting is an adaptation unique to the Seahorse’s small gill opening. The tufts extend like folds in a sheet on the inside of the seahorse to increase the surface area necessary for gas exchange in water. This allows for enough oxygen to be removed from the surrounding water to meet the Seahorses’ very basic metabolic demands. The modern Sea Dragon seen within the film has the same body plan as a Seahorse without any obvious enlargement of gill structure but with much increased metabolic demands. Seahorses in the wild are incredibly slow moving (something we will discuss later). However, the Sea Dragons seen within the film are actively carrying warriors into battle, racing across the seafloor, and are covered in what we would assume to be very heavy armor. These Atlantean steads would need much larger gill slits and likely other internal changes to maximize oxygen transport to perform these athletic feats.

Seahorses in the wild have no teeth or true movable mandible. Instead they eat prey by sucking prey through their snout into their mouth, and then swallowing it whole. They eat plankton, fish larvae, briny shrimp, and small crustaceans. They have no stomach, and instead rely on digestive enzymes from their liver and pancreatic tissues to break down their food into absorbable components within their intestines. Their digestion occurs so fast that Seahorses have a very limited time to try and absorb nutrients before the food is eliminated from their gastrointestinal systems. As a results, Seahorses have very poor absorption from their meals and must eat constantly to survive, eating up to an average of 3000 brine shrimp per day. The modified Sea Dragon seen in the film does appear to have teeth and theoretically would be able to break up its’ food (but could still grip creatures using the teeth and swallow them whole). However, again in order to meet the extreme metabolic demands generated by their activity within the film they would likely need a digestive system closer to cartilaginous or bony fish, and a ready food source. Their is a good chance that these creatures are, or at one point were, feeding on Atlanteans.

Body Plan

A normal Seahorse has an exoskeleton composed of dermal plates that although made of bone like terrestrial vertebrates, are put together using a lower overall mineral content (~40% versus the typical 65%) and a greater quantity of organic compounds. What this change in composition produces is a type of armor that that will deform and flex, but not break like typical bone. Although this mechanism has amazing benefits for a small Seahorse, and as we had discussed before, an exoskeleton doesn’t necessarily work well when scaled up for larger organisms. The Sea Dragon seen within the Aquaman film would most likely need an internal skeleton to support carrying metal battle armour, smashing into each other, and to allow Atlanteans into battle. However, this extra weight would unfortunately likely have negative effects on locomotion.

Seahorses are the slowest moving fish in the world with a top speed of about 5 ft (1.5 m) per hour. Their primary means of propulsion are the pectoral fin that is located just behind the gill opening, and the dorsal fin that joins the trunk at the tail. They rely primarily on the dorsal fin to help them move through the water with the pectoral fin acting to assist them in turns and navigation. They also have a prehensile tail that they can use to grip onto objects to resist strong tides. Despite these adaptations, many adult Seahorses die annually from changes in the weather as when trying to swim in fast currents they can be carried away or die from exhaustion. The Sea Dragons seen within the film do appear to have a similar fin arrangement to what is seen with Seahorses. If they are relying on similar types of fin propulsion to move through the water, with their increased size and skeleton, they will not be able to move through the water. The only adaptation that seems to be added is the addition of legs, that in an aquatic situation would not be beneficial. Aquatic life has developed dorsal fins as they allow for a steady and continuous means of propulsion that is focused within one location. Legs are not an ideal adaptation for aquatic locomotion.

If the Sea Dragon wanted to function within the real world, it would likely need a modified body plan closer to other fish and larger fins with adaptation for rapid propulsion in an aquatic environment.

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