Deep-Sea Creatures & Their Unique Adaptations
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As much as 95% of the available living space on planet earth lies below the waves. Yet we still know more about the surfaces of neighboring planets, like Mars, than we do about what lies at the bottom of the ocean!
One thing we do know is that there is an entire world of life lying below the surface of the ocean. Some of the world’s most fascinating creatures lurk in the depths of the sea, and we’d like to help you get better acquainted with some of them.
Ocean Depth Zones
As far as humans have discovered, the deepest point in the ocean is more than 36,090 feet (11,000 meters) down. In order to help us better understand the ocean and what lives in it, scientists have divided it into zones. The living conditions in each of these zones are vastly different. Thanks to advances in technology, we are able to explore more of the marine environment than ever.
Epipelagic Zone (Sunlight Zone)
Depth: 650 ft (200 m)
Commonly referred to as the sunlight zone, the epipelagic zone is the uppermost part of the ocean that goes down to a depth of around 650 feet (200 meters). In this zone, sunlight can freely penetrate the water meaning that organisms can use photosynthesis; in the ocean phytoplankton are the most common example of this.
Owing to the fact that phytoplankton is a food source for thousands of ocean-dwellers, the sunlight zone is where you’ll find the majority of marine life.
Mesopelagic Zone (Twilight Zone)
Depth: 650 – 3,300 ft (200 – 1000 m)
Next, we have the twilight zone which is the second layer of the ocean and dives down to depths of around 3,300 feet (1000 meters). At the beginning of this zone, where the sunlight zone ends, only 1% of sunlight can get through. As you move toward the end of the mesopelagic zone, you’re submersed in total darkness.
Despite this lack of light, there is still plenty of life here including jellyfish, blobfish, and the giant squid. Around 20% of all the world’s ocean water sits within the twilight zone.
Bathypelagic Zone (Midnight Zone)
Depth: 3,300 – 13,100 ft (1000 – 4000 m)
Fish and creatures that live in the midnight zone are essentially stuck there since they are unable to move vertically. Mainly predatory species, animals here have to sit and wait for their prey to enter their realm.
Moving to depths of 13,100 feet (4000 meters), the bathypelagic zone is bathed in complete darkness from beginning to end. It’s also pretty cold down there, with maximum temperatures not exceeding 39.2°F (4ºC)!
Abyssopelagic Zone (The Abyss)
Depth: 13,100 – 19,700 ft (4000 – 6000 m)
The next zone is the abyssopelagic zone, more commonly known as the abyss. Here, there is no light and the zone goes as far down as 19,700 feet (6000 meters). At such staggering depths, there is a total lack of oxygen on the ocean floor in this zone which means that no plant life is able to survive.
While animals in the midnight zone may have enlarged eyes to help them see in the dark, creatures here usually have very small or no eyes, as there’s simply no need for them. Instead, fish may have a heightened sense of smell, however, there is a severe lack of food down here which means the creatures have their own special set of adaptations, including extending stomachs.
Hadopelagic (The Trenches)
Depth: 19,700 – 36,090 ft (6000 – 11,000 m)
The trenches are long narrow depressions within the ocean floor that can go as far down as 36,090 feet (11,000 meters): the deepest point on earth, The Mariana Trench, is thought to be 36,200 feet (11,033 meters), but humans have not yet succeeded in reaching the bottom. The closest attempt was by a Chinese team who got down to 21,325 feet (6,500 meters) back in 2012.
These zones of the ocean account for up to 40% of the sea floor, and while they may be in complete darkness, there is still an abundance of life here, such as the supergiant amphipod.
Challenges Faced by Deep-Sea Creatures
Living in the depths of the ocean presents these creatures with a plethora of challenges. Not only are the deepest points of the ocean entirely devoid of light, but there’s a lack of food. On top of this, creatures are exposed to super cold temperatures and extremely high pressure. Life at the bottom of the ocean is far from easy!
Lack of Light
If you go any further down than the twilight zone, you’ll find yourself in total darkness. This makes life incredibly difficult, and creatures may not find it as easy to source food, find a mate, or simply navigate their habitat. As a result, creatures that live below this point have special adaptations, including using their own light sources to navigate the world more easily.
Extreme Pressures
One of the reasons that humans have, thus far, been unable to explore the deepest reaches of the ocean is that the pressure from all that water would crush submersibles. So how on earth do these creatures put up with all that pressure?
Fish do not have lungs filled with air as we do, so they cannot be compressed. However, there are some deep-sea creatures such as the beaked whale that do have air-filled lungs. Yet they’re designed differently from ours and can be compressed without causing the death of the animal.
It’s recently been discovered that deep-sea fish have molecules called piezolytes that stop them from being crushed. However, scientists are still researching how this works.
Limited Food Sources
Where sunlight does not penetrate, photosynthesis is unable to take place, so there is a serious lack of resources down in the depths of the ocean. But animals still manage to survive perfectly well here and this is because of their slower metabolisms, which means they do not need to feed as often.
While fish at these depths can and do use predatory tactics, particularly ambush, they also often feed on scraps that have fallen from the higher zones.
Cold Temperatures
Since sunlight does not get past the end of the twilight zone, the temperature in the deep ocean is very cold. However, it’s thought that these cool temperatures are partly responsible for slowing down the metabolism of the creatures so they do work in their favor.
Many of the animals that you find at the bottom of the sea are much larger than those nearer the surface. Their larger size means more body fat and this helps to regulate their body temperature.
Common Adaptations in Deep-Sea Creatures
In order to survive at the bottom of the ocean, creatures have a series of adaptations that help them hunt, navigate, find mates, communicate, and more.
Bioluminescence
Bioluminescence is a chemical reaction that causes animals to create their own source of light. This often happens as a result of photophores and luciferin and this chemical is typically absorbed by the animal-eating creatures that contain it.
Many fish and other species that live in the lower zones of the ocean are bioluminescent and they use this for several reasons. Some animals, like the angler fish, have a bioluminescent lure that they use to attract prey. Others, like the vampire squid, use their bioluminescent ink to distract predators.
Bioluminescence is actually the most common form of communication on planet Earth and deep-sea animals may use flashing patterns or colors to attract a mate or as a warning.
Pigmentation
Where there is no light, there is not so much need for color. In fact, right down there in the far depths of the ocean, some colors aren’t even visible as they’re totally disappeared from the light spectrum.
To remain camouflaged, creatures down here usually come in darker colors like red or black. Others may be transparent as this keeps them hidden from predators.
Big Eyes
When you get down past 9,840 feet (3000 meters), there is no light, so of course, this makes it difficult to see. However, one of the adaptations of deep-sea creatures is large eyes which allow more light in and make it easier for the creature to navigate. Their eyes also have more cones than animals that live in lighter conditions, further making it easier to see in the dark.
Some creatures, like scallops, have mirrored eyes made from a natural substance called guanine, which allows the eyes to work just like a telescope!
However, the further down you go, the smaller some eyes get and there are some very deep-sea creatures that have no eyes at all; they’re simply not needed.
Squishy Bodies
With the pressure so high in the deeper zones of the ocean, many creatures have squishy bodies that are more easily able to withstand this pressure. Examples of this include the blobfish that is able to put up with 1000 lbs (450 kg) of pressure owing to the fact that its gelatinous body is almost the same density as water.
Fish at these depths often lack bones, and their internal organs are a lot squishier and able to be compressed. In most cases, the animals lack swim bladders, and where they do have them, they’re filled with water, not air.
Deep-Sea Gigantism
If you compare certain invertebrates in the lower zones of the ocean, they are typically much larger than their cousins that live closer to the surface. This is called abyssal gigantism and is thought to exist owing to the lack of food and more challenging conditions these creatures are exposed to.
Larger animals are able to travel further and cover a wider area when looking for food and their bodies are able to withstand a lot more pressure. Their size could be the key to their survival. What’s more, some scientists suggest that animals down here are not having to exert as much energy to regulate their body temperatures which means that energy is distributed to other functions.
Reduced or No Swim Bladders
A swim bladder is an organ possessed by fish that allows them to control buoyancy. This benefits the fish as it does not need to put as much energy into swimming. However, since swim bladders are filled with air, they would become crushed when moving to deeper parts of the ocean.
Therefore, fish down here tend to lack a swim bladder or, if they do have one, it’s far smaller in size. On top of this, the swim bladders of deep-sea fish contain lipids instead of air which prevents them from floating up.
Antifreeze Proteins
Owing to the super cold temperatures in the deeper parts of the sea, some animals, like the Antarctic ice dragon, have proteins in their blood that act like antifreeze. These proteins prevent the blood from freezing and allow it to flow freely despite the cold.
The proteins actually stop ice crystals from forming in the fish’s blood and act as a cushion that sits on the sharp edge of an ice crystal, stopping it from developing even more.
Wider Mouths & Elastic Jaws
One of the reasons that a lot of deep-sea creatures have larger mouths is to enable them to eat anything that comes their way. Since food is scarce down here, they can’t afford to be picky, and having a wider mouth means there’s a higher chance of food entering it. In some cases, these wide-mouthed fish will simply lie on the seabed, mouth agape, waiting for prey to just crawl in.
The jaws of these fish also tend to be less bony and more flexible, allowing them to open their mouths even wider. There are some examples of fish that have no jaw at all such as the hagfish.
Sea Creatures that Live in the Depth of the Oceans
There are thousands of species that we know live in the depths of the oceans and plenty more are still to be discovered. With more than 300,000,000 square miles of seabed that has mud more than 3,280 feet (1000 meters) deep, it’s no wonder we aren’t aware of many of the creatures that live down there. But here are some that we do know about.
Barreleye Fish (Macropinna microstoma)
The first barreleye fish was discovered by humans in 1939. But despite research having come a long way since then, still not a lot is known about these animals and their lifestyle and breeding habits.
One of the most notable things about the barreleye is its big tubular eyes and transparent head. Until recently, it was thought that the eyes were fixed but we now know that they can rotate, viewing prey above it through its transparency. What’s more, being able to see up allows them to spot jellyfish so they’re not stung while feeding.
Barreleye fish can be found at depths of around 2,500 feet (800 meters). They live around the waters of Japan and as far west as California.
Sea Spider (Pantopoda spp.)
While it may be called a spider, the sea spider isn’t a spider at all; it’s actually a type of arthropod. They’re found in the Antarctic ocean as well as around southern parts of Africa and South America.
It’s thought that there are around 1000 species of sea spiders, some of them with leg spans up to 28 inches (70 cm)! While there are examples of sea spiders in shallow waters, some species can live at depths of up to 7,000 feet (2,100 meters).
To survive at the bottom of the ocean, these creatures have long legs that enable them to move across the ocean floor. Their bodies are so small that some of their internal organs can be found in these legs.
Goblin Shark (Mitsukurina owstoni)
Goblin sharks can get very big and some will grow up to 18 feet (5.5 meters) in length. They typically live at depths of around 3,000 feet (900 meters), but they’re known to dive even deeper as they get older.
These obscure-looking sharks resemble something out of the Labyrinth movie and can be found in the Atlantic, Pacific, and Indian Oceans.
Their snout looks like a long sword coming off the front of their heads, and the teeth are super sharp. However, this long snout allows the fish to sense electric fields, which aid it in hunting and navigation.
Goblin sharks have a narrow, flabby body that allows them to withstand the pressure in the deep ocean.
Frilled Shark (Chlamydoselachus anguineus)
The frilled shark may live at depths of up to 3,300 feet (1000 meters), it was discovered some time ago back in 1879. These odd-looking deep-sea sharks have 25 rows of teeth and are truly the stuff of nightmares! However, while they may look like toothed eels, they actually hunt in a way that’s much more similar to a snake.
What’s more, it’s thought that the large, oil-filled liver allows the shark to float through the water without the need to swim. However, we’re still not overly clued up on the frilled shark, as any specimens that have been brought to the surface have quickly perished.
It feeds on bony fish and cephalopods and spends most of its time close to the ocean floor. You’ll find these sharks in the Atlantic Ocean and around the outer continental shelf.
Blobfish (Psychrolutes marcidus)
The blobfish has been dubbed the ugliest fish in the world by many and it even spent some time as one of the most popular memes on the internet. However, their strange appearance only happens when you take them out of the water. Under the waves, the pressure causes the blobfish to look more normal.
Blobfish live anywhere between 2,000 and 4,000 feet (600 and 1,200 meters) and are common around Australian waters, where they’re put under up to 120 lbs (54 kg) of pressure. Their lack of a swim bladder and gelatinous bodies help them to cope with this.
Vampire Squid (Vampyroteuthis infernalis)
The vampire squid isn’t actually a squid at all. This is a creature in a family of its own, and it’s the last surviving member. So ancient is the vampire squid that it’s called a living fossil.
These creatures may have a horrific name, but they’re gentle animals that scavenge marine snow around the deep ocean and can be found all over the world in tropical and temperate waters. Typically, they don’t grow to more than a foot in length.
They have gelatinous bodies with tentacles that are connected by webbing. First discovered in 1903, the vampire squid has bioluminescent eyes to help it see at depths up to 3,000 feet (900 meters).
Deep Sea Anglerfish (Melanocetus johnsonii)
The deep sea anglerfish is one of 200 species of anglerfish and is probably one of the most well-known deep sea creatures. They have a long lure at the top of their heads that glows using bioluminescence to attract prey. They can even wiggle it to make it more appealing.
These bony fish have large mouths with fangs which are typical of carnivorous animals. You’ll find these fish throughout the world’s oceans, but they are rarely observed in their natural habitat, so there’s still lots more to discover about them.
Amazingly, the males will attach to the female, providing her with sperm for mating. A single female can have up to six males permanently fused to her.
Snipe Eel (Nemichthys scolopaceus)
Snipe eels are found all over the world and are sometimes called threadfish owing to their incredibly slim bodies. They’ll grow to around 5 feet (1.5 meters) and live at depths of up to 6,000 feet (1,800 meters).
These long, thin creatures have a continuously open mouth with a beak-like jaw, so they’re ready to swallow up prey at any given moment. Inside the mouth are backward-facing teeth that prevent prey from getting out once inside.
The snipe eel can lay claim to having the most vertebrae out of all known creatures, with around 750 along the entire body!
Humboldt Squid (Dosidicus gigas)
Sometimes called the Jumbo squid, these animals of the deep can grow up to 5 feet (1.5 meters) in length. For humans, they are incredibly important for commercial fishing, but there’s a lot of concern around them since they can be very aggressive.
In fact, it’s been reported that, when caught, they become highly aggressive, and since they flash red lights when they feel threatened, they’ve been aptly nicknamed the red devil!
Humboldt squids usually live in depths up to around 2,300 feet (700 meters) and they have as many as 100 to 200 suckers on each of their tentacles. They’re most commonly found around South America, but they’re beginning to migrate north, and some have been seen as far up as Canada.
Fangtooth (Anoplogaster cornuta)
The fangtooth has seriously long teeth and compared to other deep-sea fish, their teeth are the largest in comparison to their bodies. They use these teeth as a weapon to catch prey and can sometimes be seen hunting in groups, although they prefer to hunt alone. But they don’t use any special tactics and largely rely on literally bumping into their food.
Out of all the deep-sea fish, fangtooths have been noted to survive the longest in aquariums, although it’s not a very good idea to keep them, as they’ll perish in the end, and it won’t be pleasant for them.
Fangtooth fish are some of the deepest ocean dwellers at up to 7,400 feet (2,200 meters) and they’re found all over the world, particularly off the coast of Australia.
Giant Isopod (Bathynomus giganteus)
The giant isopod is related to things like crabs and shrimp, but while it’s classed as a crustacean, it’s also a very close relative of the pill bug that you’ll find in your backyard. Only, under the ocean at depths of up to 2,000 feet (600 meters), they can grow to around 16 inches (40 cm)!
These animals are scavengers that have seven pairs of legs. The first set of legs doubles as a mouthpart which the creature uses to draw in food. They’re typically found wandering around the ocean floor, and there are as many as 20 species of giant isopods currently known to humans.
Giant isopods are found in all three of the major oceans; the Atlantic, the Indian, and the Pacific.
Giant Tube Worm (Riftia pachyptila)
Giant tube worms were only discovered in 1977 and a whole ecosystem was discovered 8,000 feet (2,400 meters) below the surface of the ocean.
These creatures have a symbiotic relationship with a type of chemosynthetic bacteria. Since they have no eyes or no gut, it would be impossible for the giant tube worms to hunt and feed. However, the bacteria provide them with nutrients in exchange for a protected home beneath their hard shells.
The giant tube worm can grow up to 9 feet 10 inches (3 meters) and is found around hydrothermal vents at the bottom of the sea. These benefit the worms as they create a natural ambient temperature.
Venus Flytrap Sea Anemone (Actinoscyphia aurelia)
Around the Gulf of Mexico and in some parts of the ocean off the coast of West Africa, you’ll find the venus flytrap sea anemone which looks remarkably like its terrestrial counterpart. What’s more, they feed in the same way, closing their tentacles around their prey which is usually debris that has fallen from above.
The venus flytrap sea anemone only grows to around 12 inches (30 cm) and typically attaches to rocks, although it’s also common in muddy areas. They can live at depths of up to 6,660 feet (2,000 meters)!
Gulper Eel (Eurypharynx pelecanoides)
The gulper eel looks pretty normal until it opens its mouth which is super wide and resembles that of a pelican which is why this animal is commonly referred to as the pelican eel. Their enormous mouths are around a quarter of the size of the entire creature and can swallow animals much larger than they are. Despite this, they’ll usually only prey on small crustaceans.
Gulper eels are found all over the world in both tropical and temperate waters, and they will live at depths of up to 9,990 feet (3,000 meters).
On the tip of the tail, the gulper eel has a small bioluminescent light that it uses as a way of attracting prey in the darkness.
Snaggletooth (Astronesthes niger)
The snaggletooth is one of 49 species, with the Richardson snaggletooth being one of the most common. They’re usually found in warmer parts of the Atlantic Ocean, but it’s not uncommon to also find them in the Pacific and Indian Oceans as well.
These fish have large mouths and sharp teeth which help them to catch their prey. However, down in the dark depths up to 2,800 feet (850 meters), they have to use a red barbel on their chins to attract prey which is usually things like small fish, crustaceans, and the lanternfish.
Black Swallower (Chiasmodon niger)
Black swallowers live at depths of up to 9,000 feet (2,700 meters), so they’re one of the lesser explored fish. However, when they die, it’s not uncommon for them to float up to the surface where people have often mistaken them for a floating deflated tire.
This is because of their enlarged stomach which is one of the features that allows the black swallower to eat fish four times its own size. Additionally, a large mouth helps with this, but the rest of their body is comparatively narrow.
These fish are found in tropical and subtropical waters but are most common in the North Atlantic. They typically grow to between 6 and 8 inches (15 and 20 cm).
Hoff Crab (Kiwa tyleri)
One of the most interesting things about the hoff crab is where it gets its name. Before it was given its proper scientific name, kiwa tyleri, the crab was lovingly dubbed the hoff crab after the Hollywood actor of the same name; David Hasselhoff, or The Hoff, for short.
This was because of the bristles and bacteria on the crab that made it appear just like the bare, hairy chest for which the actor is famous.
These crabs can live as far down as 7,800 feet (2,400 meters) and are found largely in Atlantic waters. They thrive around thermal vents, and the only time they’ll leave is to lay their eggs which wouldn’t survive the hot temperatures around the vents.
Harp Sponge (Chondrocladia lyra)
The harp sponge, sometimes called the lyre sponge, is found primarily in the Pacific Ocean, and they’re one of the deepest dwelling creatures on this list, living as far down as 11,500 feet (3,500 meters)! However, we weren’t even aware of these creatures until recently since they were only discovered in 2012.
The harp sponge is a filter feeder that mainly eats bacteria. It catches its prey through velcro-like filaments that catch it as it passes. The sponge anchors itself to the seabed using its rhizoid and from this, there are up to six branches that give it its harp-like appearance.
Viperfish (Chauliodus spp.)
Looking at the viperfish, you’ll immediately notice its long, needle-like teeth which it uses to immobilize its prey down there in the dark. These fish are normally found in warmer, tropical waters and have a large hinged jaw that allows them to swallow up prey.
The fish attracts its prey through bioluminescence and uses photophores to create dots of light along its body. Once it catches its prey, the angled teeth prevent it from escaping.
Viperfish live down to depths of around 3,200 feet (975 meters), but some are known to swim a little higher than this. Normally, this happens during the night when vertical migration is common among the species.
Lanternfish (Symbolophorus barnardi)
We are currently aware of more than 200 species of lanternfish and they make up as much as 65% of all life in the deep ocean. However, while they stay at depths of up to 2,600 feet (800 meters) during the day, they vertically migrate at night in search of food.
These small fish don’t get much bigger than six inches, but they have enormous eyes in comparison to their bodies. This helps them see in the deeper water, but they also use bioluminescence with photophores in the head. The light they produce is used to attract small fish, on which they prey, but is also thought to aid in mating.
Giant Squid (Architeuthis dux)
Perhaps one of the most terrifying and mystical creatures of the deep ocean is the giant squid. They were the stuff of legend until 2004 when a Japanese team finally managed to capture a photo of a live one. Otherwise, all we understand about them comes from the bodies that are washed up on shore.
These mammoth animals can grow up to 60 ft (18 meters) in length and live at depths of up to 3,200 feet (975 meters). They’re normally found in the Atlantic Ocean as well as parts of the Pacific, but they tend not to live in polar or tropical regions.
Not only are these massive creatures, but they have eyes the size of basketballs! They’re also known to be incredibly intelligent with complex brains and are thought to be the smartest of all marine invertebrates.
