Terrors of the Deep | An Introduction

The ocean. It’s a scary place. Despite the fact that the ocean covers 60-70% of our planet’s surface, humans have explored less than 5% of it.  We know less about it than we do about the surface of the moon.

**Terrors of the Deep will be a four part series covering the mysteries of the deep sea and the life that dwells there.

…If this isn’t creepy enough for you, consider the ocean’s immense depth. This image will give you an idea of the maximum known depth of the ocean (10.9 km or 6.85 miles, at the Mariana trench in the Pacific Ocean).

Let me put that into perspective.

Mt Everest, the highest peak on Earth, reaches 8.89 km (or 5.49 miles) above sea level.  The ocean is as deep as the height of Mt Everest and then some. Think about your local swimming pool. The deep end is generally about 4 m deep (about 13 ft). Times this by 2725 and you have the depth of the Mariana trench (http://i.imgur.com/NT5eO.jpg)

Let’s first go over some basic oceanic anatomy, shall we? (n.b: all mention of the deep ocean in this post will refer to the Bathypelagic zone and below).


© Vibhuti Patel

Something about the deep ocean talks to our brains. It ignites our imaginations and brings forth pictures of all kinds of weird things. Part of this is probably due to our history. Humans have long had a kind of love/hate relationship with the sea, and fantastic tales of colossal denizens of the deep have long plagued our imaginations. Sea monsters play prominent parts in mythology, ancient culture and even cryptozoology (Nessie, anyone?).

The reality is that the ocean is an ecosystem which means it is flourishing with biodiversity, and we don’t actually know if this includes the mighty sea monsters of old (yet!).

Abiotic characteristics of the deep ocean


Life is essentially supported at its core by the light of the sun, which allows the generation energy via photosynthetic organisms. But in the ocean, light is inadequate for photosynthesis below 200 m, and by 1000 m it’s as dark as the darkest night.


Because of the lack of sunlight, the deep ocean is also incredibly cold. With the exception of hydrothermal vents (more on this later), the deep sea hovers consistently around the -1°C to 3°C (30.2 F to 37.4 F) mark.


Another characteristic of the deep ocean is pressure. Anyone who has gone scuba diving will know that you can feel significant pressure change even at a measly 10 m (33 ft) down. Your ears certainly complain about it. This is because at 10 m the pressure is double that which is found at the surface (i.e sea level).

Keep going to 20 m (65 ft) and the pressure is three times that of the surface.

Now, imagine the amount of pressure at 10,900 m (35,700 ft) deep, and the weight of however many megatons of water bearing down on your head. It would be enough to reduce a human into nothing more than an organic meatbag; a sack of goopy mess. We would be much more than merely squished.

The deep sea is also notoriously scarce in terms of food supply, and some places are very oxygen-poor.

So given these seemingly inhospitable conditions, how in the name of Neptune do things survive down there?!

Evolution, that’s how!


What do you do if the environment doesn’t give you light? You make your own, of course!

Using the chemical process of bioluminescence (literally, living light), many species living in the deep sea are able to create their own light. It’s thought that this helps them in the following ways:

  1. To see (bit of a no-brainer, this one).
  2. To allow social communication with other conspecifics (i.e attracting mates)
  3. To lure prey (cue creepy anglerfish image in brain)
  4. To hide from predators (in the case of fish that produce blue light on their bellies that exactly matches the hue above them, effectively making them invisible from below)
  5. To confuse predators; using bright flashes to stun them and make a quick getaway.

By definition, bioluminescent light is usually a ghostly blue/green colour because these are the colours that travel furthest when under water. In fact, many animals that live in the depths have actually lost the ability to see red light completely. This has been exploited by the fearsome dragonfish, who is able to both see and create red light. They are therefore able to locate prey without them even knowing. Eek.

Big eyes

Some creatures of the deep sea have grown eyes that are way too big for their heads. This allows them to take in as much light as possible. The below was actually found by a man in Florida as he walked along a beach. Experts say it may have come from a giant squid, but that if that was the case it is on the smaller side – they are known to have eyes that grow to the size of footballs. Imagine that!

Reliance on other senses

Since sight is so hard to come  by, many animals depend heavily on other senses to help them understand their environments, like smell, touch and even taste. A unique feature of many deep sea fish is the lateral line, which is a sense organ that helps them detect movement and vibrations in the sea.

Body composition

Warning! The explanation I’m going to give about how animals survive in the deep with regards to pressure is going to get a bit physics-y, but I’ll try and keep it as simple as possible.

At Earth’s surface, we are so well accustomed to the atmospheric pressure that we don’t even feel it. But, as I described earlier in the post, animals living in the deep sea have to contend with the immense crushing pressure generated by the weight of water above them.

The reason we and many other mammals don’t do so well when diving in the ocean is because of the air pockets inside our bodies (lungs, sinuses etc). Gasses are extremely compressible. They expand or shrink to fit the volume whatever they’re contained in. So when we dive in the ocean, the air pockets in our bodies shrink due to the change in external pressure.

Solids and liquids, on the other hand, are virtually incompressible. In fact, you could squeeze a solid or liquid-filled container as much as you like, and its volume would remain pretty constant. Deep sea creatures therefore have bodies that contain very little to no air pockets. Take the giant squid. Its flesh is solid, and its blood liquid. The lack of air space in its body means that it is basically entirely incompressible. The pressure inside the squid matches the pressure outside it, so it’s able to not get crushed. Many marine creatures share similar compositions.

Marine snow

Without sunlight, energy (food) is not able to be made. Deep sea animals are therefore reliant on food that floats down from the surface. This could be anything from particles of organic material or the gigantic carcasses of whales and other things. Yum.


Featured image is sourced from https://i.imgur.com/guMCFeF.jpg. 


2 responses to “Terrors of the Deep | An Introduction

  1. Pingback: Terrors of the Deep | Part 1 | shudder·

  2. Pingback: 51 Facts To Know Before You Die – Funblab·

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