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Fantastical Biology – Part Four: Deep Ocean

Sea Monster by NgJasThe ocean covers 70% of the Earth’s surface, and yet humans have explored less than 5% of them. No wonder the deepest parts of the ocean have inspired and played a part in so many speculative fiction stories, like Twenty Thousand Leagues Under the Sea, or China Miéville’s The Scar. Dolphins, seals and manatees are probably where myths about mer-people originated from, and you might know the giant squid better as the kraken. Modern technology has allowed us to get a look at the bottom of the ocean, and many of the creatures down there look like they belong in a fantasy novel.

If the setting for your story is Earth, then it shouldn’t be too difficult to incorporate the information and ideas in this article to create realistic underwater fantasy creatures. So much of the ocean is still a mystery, and scientists are discovering new species all the time, so the deep ocean is a great place to let creativity run wild. Or use our oceans and their inhabitants as a template for creating an original fantasy world.

The Abyss

Water dragon by Jaemin KIMAs mentioned in some of the previous articles in this series, creating a fantasy creature is easier if you know what the environment—the story’s setting—is like. So, what is it like living in the deep ocean? The most well-known marine creatures live near the ocean’s surface, where light is still able to penetrate. Below 200 meters, the light starts to fade, almost like a sunset, so the deep water is illuminated blue and purple. Finally, 1000 meters down, there is no light at all. Just the dark, and the cold, and the crushing pressure of the ocean on all sides. Some animals in this area live their entire lives without touching a flat surface. A mermaid who lives in the open ocean might find the concept of a floor strange, should she take an interest in humans.

Swim down far enough, and you eventually reach the ocean floor. The “dirt” is decaying bits of once-living creatures. No wonder it’s called the Hadal zone, after the Greek god of the underworld. But it isn’t just an endless undersea graveyard. There are volcanoes, hydrothermal vents (like underwater geysers), and even coral reefs. Stranger still are the underwater lakes and rivers, which are mixtures of very salty water and hydrogen sulfide.

Snow for Dinner

whale carcass by Michael RothmanOn land, the food chain starts with plants. But there’s no light at the bottom of the ocean, so any fantasy creature living down there will have to find some other source of food. Remember how bits of dead things are floating through the ocean on their way to the bottom? It’s called marine snow, and is one of the most important food sources for deep sea animals. While nibbling on marine snow is nice, a whale fall is like going to an undersea feast. When a whale’s body reaches the ocean floor, it creates an ecosystem that can last for a decade.

A species of nomadic fantasy creatures might move from whale to whale, pitching up kelp or shell tents for a few years before moving on to the next one. Or they might have a village near one of the hydrothermal vents, or on the shores of an underwater lake. Bacteria can live on the toxic substances in these areas, and other creatures in turn live off of them. They create thriving communities where scientists once thought no life was possible.

Glow-in-the-Dark Fish

So far we’ve talked about what a marine creature’s habitat and diet will probably be like, but what might they look like? With names like Swallower, Loosejaw, Viperfish, and Goblin Shark, it’s obvious they’re scary looking. Don’t Google them if you’re planning a trip to the beach.

Water Dragon by ConejoBlancoBecause there is no light, many deep sea animals produce their own, called bioluminescence. Jellyfish are well-known for this. The angler fish, of Finding Nemo fame, uses a lure that glows to attract its prey. Some deep sea animals will have very large eyes, like the giant squid, or are blind and use their other senses to find food and avoid predators. A few creatures that live down there are also transparent, to better blend with their surroundings and avoid detection.

A community of fantasy creatures might harvest glow-in-the-dark creatures to light their cities with, much like a fire-fly lamp. Or if your protagonist notices an unnatural glow over the side of his ship at night, it might just be a mermaid, come to say hello. Or eat him. No one said mermaids have to be friendly.

While many deep sea creatures are small, there is an effect called abyssal gigantism, where creatures grow to be much larger than their shallow-water cousins. Giant squid are one example of this, but there are also crabs that can reach 3.8 meters from one leg to the other. The giant isopod looks like a pill bug the size of a house cat. Much of the plot of The Scar revolved around catching a giant fish of the deep, and having a creature bigger than the boat right beneath it is great for creating tension in a story.

Magical Deep Sea Diving

Deep Diver by randisWhat’s the point of creating a thriving fantasy ocean if none of your (probably land-dwelling) characters can get there? If the story is set in our world, there are submersible vehicles that can reach the deepest parts of the ocean. If you’re looking for something with a little less technology, consider the bathysphere, which reached half-a-mile beneath the ocean. This is a metal sphere with two thick quartz windows lowered into the ocean from a boat. There’s no motor, and the divers have to bring their own air supply. It had a light and a telephone cable for communication with the surface. But if your story world isn’t that technologically advanced, perhaps the diving crew brings a wizard along, who uses his magic to communicate with the surface and provide light to see by.

The entire ocean has a bit of the fantastical about it, from the deepest trench to the shallow waters of a tropical coral reef. Let your protagonist’s dangle their toes in the water, and wonder what’s down there.

Title image by ConejoBlanco.



  1. […] next article in my Fantastical Biology series is up. This one is about life in the deep oceans, and how to apply that in a fantasy […]

  2. Some good toughts here, though I think there might be some mixing up between the deep ocean floors and shallow coastal waters. While both look the same on the surface, down at the bottom they are completely different kinds of environments. The deep sea, where you have the volcanic vents, bacteria, giant squids, and anglerfish are a vast barren dessert, while the coastal shallows, particularly in tropical waters, can be more like thick jungles full of plants and much more common looking animals. These regions are often only 10 to 20 meters below the surface, with lots of light and relatively warm water. That’s where you would find the mermaids with tools and decorations made from kelp and shells. Creatures native to such an environment would be unable to survive in the deeps of the ocean floor.
    It’s a bit like the difference between living on the surface of the land, and an entire second world deep below the ground. I think it’s probably good in most cases to retain a distinction between those two.

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