As night falls on oceans across the world, millions of deep-sea creatures begin a long journey. They swim up towards the surface where food is more plentiful, often travelling half a kilometre or more for their meal. This is called "vertical migration" — keep reading to learn more about it and the creatures that take part in it every night.
The sparkling enope squid is bioluminescent. It spends its days at depths of several hundred metres and returns to the surface at night. (Wikipedia)
This event, which takes place night after night, is known as the vertical migration. Creatures from the deep make this long trip in the darkness because predators are less likely to spot them. They feast on food in the shallower ocean waters throughout the night. And before daylight returns, they descend into the safety of the deep, dark sea once again.
Light refracts off the comb-rows of the ctenophore Mertensia ovum producing stripes of rainbow colour. (Wikipedia/Public Domain/National Oceanic and Atmospheric Administration)
Creatures living in the deep ocean must survive in almost complete darkness. But many animals who are found at these depths are bioluminescent—that’s a fancy way of saying they produce light. Using chemicals in their body, they are able to glow in the dark.
A bioluminescent salp, or Pelagic colonial truncate, off Ataura Island, East Timor. (Wikimedia/Nick Hobgood/CC BY-SA 3.0)
These creatures use this ability for a variety of reasons. Some rely on their light displays to hide from predators. Others use light to attract prey. And still others count on their bioluminescence to distract enemies or attract a mate.
Get an up-close look at some of the sea creatures who take part in the nightly vertical migration.
This strange creature gets its name from its similarity to the cockatoo bird - its tentacles gather like a feathery crest above its head. But it's also commonly known as glass squid. Found in the depths of tropical oceans, it has a see-through body.
When it feels threatened, it squirts ink inside its body which camouflages its internal organs, allowing the squid to become practically invisible to enemies. It also has light cells under its eyes that give off a shadowy glow. This is often mistaken by predators as dim light coming from the surface, so they don't notice the squid itself.
Bloody Belly Comb Jelly
While the comb jelly looks similar to a jellyfish, it's a very different animal. Although they both have transparent bodies, the bloody belly comb jelly comes in different shares of red. And as you'd imagine by its name, its stomach is always blood-red. This colour looks black in the darkness of the sea, which makes it hard for predators to detect it.
One of the comb jelly's most interesting traits is the way it moves - it has rows of tiny hair-like structures called cilia running up and down its body. By constantly moving these cilia back and forth like a boat's oars, the jelly propels itself through the water.
At first glance, it appears that this fish's eyes are just above its mouth - but those are actually the barreleye's nostrils! To spot its eyes you'll have to look inside its head. Yes, inside. The fish's eyes are found inside its see-through head. This clear covering protects its eyes as it snatches small prey from the stinging tentacles of jellyfish.
The fish's green eyes are highly sensitive to light, which helps it see in its dark ocean habitat. They eyes also swivel in many directions, allowing the barreleye to look upwards and search for the faint shadows of prey swimming by overhead.
This small fish is one of the most common creatures found the world's oceans. As its name suggests, the lanternfish has the ability to produce light. Its skin is covered in tiny light organs known as photophores. Found on the fish's head, underside, and tail, these organs light up as the fish swims. This light may lure small prey close enough to become dinner, and it may help confuse predators so the fish can make a quick escape.
Besides giving off light, there's another thing about this fish that's hard to miss. It has very large eyes. Big eyes are quite common in creatures of the deep. They help the animals collect as much light as possible so they can see in their pitch black home.
Meet one of the fiercest predators of the deep. The viperfish has sharp, fang-like teeth that don't fit inside its mouth, giving it the look of a true monster. And you can bet the viperfish puts these spiky teeth to good use. It swims at high speeds toward its prey and spears its meal with them.
The viperfish has another secret weapon to snag dinner - a light producing organ found on the tip of a long fin on its back. The fish floats motionless for hours, waving this light in the dark waters like a lure. The glowing light attracts the attention of unsuspecting fish and when they come in for a closer look - whoosh! - the viperfish goes into attack mode.
This creature is actually made up of a colony of individual animals known as zooids. They are attached and work together to survive as one. Some part of the siphonophore are responsible for catching prey, others digest food, and still others help the colony to swim through the deep sea. This string-like colony can be arranged in chains that measure a whopping 40 m long. That's longer than a blue whale, making the siphonophore among the longest creatures in the world!
The colony uses stinging glowing tentacles to capture small fish, and then use these to inject a toxin into them. This prey then becomes a meal for the entire colony.