The Mystery of Earth's Greatest Migration

Perhaps you envision enormous herds making their annual journey across the Serengeti or transcontinental planes when you think of the largest animal migrations on Earth. every year, the sky is painted orange. The largest mass migration on Earth, however, takes place undersea every single night. Submarine Sonar captured these odd, thick signals emerging from the depths during World War II, which appeared to be the ocean bottom shifting up and down by up to 3,000 feet in some places. The ocean floor was still. The sonar was actually picking up vast swarms of the microscopic zooplankton, which were nightly rising from the depths to the top and descending again. It turns out that this occurs every night in every ocean, which absolutely perplexed scientists.

Why, exactly, do these minuscule plankton

such a fantastic daily journey?

It turns out that the solution may be connected to seemingly unrelated phenomena like biological clocks.

and even global warming.

Hello, Amy here. This is the odd tale of the biggest and most enigmatic migration in Earth's history.

The largest net animal movement on our planet is vertical migration.

It's very amazing.

Therefore, you must first recognize how little zooplankton are.

Even though they are really small—like smaller than the tip of a pencil tiny—the distances they travel in the ocean are absolutely enormous.

You would have to run a 10K twice a day if we scaled the migrations to a human,

once to get your breakfast and once to go to bed

but you'd have to swim at twice the speed

of an Olympic marathon runner.

It's a fairly amazing attempt that takes place every single day.

When the vertical migration is totaled

Scientists estimate that 10 billion tons of biomass, or 25 times the mass of all people on Earth, are moving between the surface and the deep every night in all of the world's oceans and lakes.

The diel vertical migration, or simply DVM, is what it is known as.

But why take the time and effort?

Undoubtedly one of the most frequent activities we observe in the water is vertical migration.

Migrators are typically small fish like bristlemouths and lantern fish that are following the vertical migrations of the zooplankton. They range in size from some of the tiniest to some of the largest and most abundant, in terms of biomass.

It is a very unusual way of thinking since, although plankton may make decisions, we typically conceive of them as wanderers like the Greek name for plankton describes them.

Zooplankton are creatures of the shadowlands.

No, not that twilight zone, but some do seem a little off.

We're referring to the mesopelagic zone, a portion of semi-deep water that only receives around 20% of the light that is present above the surface.

Well, we know that this vertical movement by the animals is a true dance, a balancing act by them to try to get food, which is most abundant in the surface waters where photosynthesis allows things to grow, while they're trying to avoid becoming the dinner for something else, so if you're trying to avoid getting eaten, you wanna be in the dark.

Therefore, what we typically observe is that creatures spend the day in the deep dark and then migrate to the surface when the sun sets before setting out again at sunrise.

They would travel up the water column at dusk and then back down at morning in response to minute variations in light.

However, there are situations when organisms act in the other way.

Reverse diel vertical migrations are sometimes referred to as.

According to research, zooplankton can migrate up to 200 feet in the water only by passing through clouds.

That implies that they are shockingly photosensitive.

However, scientists believed the situation might be more complicated.

We're use sound, just like the first viewers of diel vertical migration.

When we try to descend with a camera that has many lights, we're lucky if we can see a few arm lengths in front of us. However, sound travels both further and faster in water than it does in air, so we can get a really large scale picture of what's happening with animals very quickly.

So, using both traditional tools like nets and cutting-edge methods, such as searching for signs of the DNA that these animals leave behind in the water column, we combined those sonar observations in which we send out a brief pulse of sound and interpret how it echoes off the animals in the habitat.

To get a whole image of what's happening far away from what we can ever view when aboard a ship at the surface, we sort of mix all these distinct lenses.

Thanks to all of this cutting-edge research, scientists have discovered that DVM is caused by factors other than merely fluctuations in sunshine.

Scientists researching zooplankton in the Arctic, for instance, discovered that throughout the long, dark winter, zooplankton responded to moonlight instead.

Thus, the way scientists think about things has completely changed in light of all this new information.

Well, it's completely altering everything we know about plankton.

Okay, so phytoplankton is a different category of plankton.

The majority of the oxygen we breathe actually comes from them since they perform photosynthesis.

Some phytoplankton and photosynthetic plankton are capable of vertical motion.

These are extremely small, microscopic organisms that resemble plants and float constantly with the currents while still having control over their vertical movement.

They have swimming organs and the ability to control buoyancy.

However, most of the time, we see that they spend the day gathering sunlight to photosynthesize and then migrate deep into the water column at night to take advantage of better nutrition levels at deeper depths.

By thinking about light and the nutrients they need to thrive, they are sort of moving the balance away from worrying about food and predators.

But there's more. DVM research may be able to shed light on our own circadian rhythms, the biological clocks that keep our bodies on schedule.

The Latin phrase circa diem, which translates to "about a day," is where the word circadian is derived.

Since many of our daily habits are governed by circadian rhythms, that is actually quite appropriate.

Additionally, the majority of surface-dwelling species, including humans, have a hormonal system, a portion of their brains, and an internal biological clock that regulates a variety of bodily functions, from appetite to sleep to reproduction.

If you are a living thing that inhabits the land, light or a lack of light causes the release of chemicals that indicate when it is appropriate to carry out specific tasks.

For example, if you were a bee, these compounds might make you go out and search for pollen.

It can entail shifting a plant's blooms in a new direction.

Humans also begin releasing melatonin, a hormone that aids in relaxation and sleep, when it becomes dark outside.

Additionally, when it's light outside, we create less melatonin, which keeps us alert.

As a result, we have a lot of knowledge about how these rhythms function in organisms that live on land, but for aquatic life, Circadian rhythms have largely remained a mystery.

Do plankton even have them, for instance?

Or do they simply behave like little robots attracted to light like a moth to a porchlight?

Well, in 2017, while examining zooplankton in the lab, researchers discovered that the organisms not only moved up and down during a typical day-to-night light cycle, but they also continued to move even when the lights were always off.

This suggests that these tiny water creatures, which resemble alien life forms, may also have a circadian rhythm.

However, one of the most bizarre things we're seeing as a result of studying vertical migration is that it may contain the secret to addressing the greatest common threat facing humanity today—climate change.

The biological carbon pump heavily relies on vertical movement.

At the surface, photosynthesising organisms remove carbon dioxide from the atmosphere.

If it simply remains on the water's surface, it will be released once more into the atmosphere.

However, if it enters the deep sea, it can remain there for a very long time.

Therefore, the consequences of the climate change caused by carbon dioxide are diminished by removing it from the atmosphere and dumping it in the deep sea.

That was done by the ocean.

About 25% of the CO2 that we emit is absorbed and sequestered by the ocean each year.

A very quick approach to do that is by vertical migration.

And all of this emphasizes the need of understanding diel vertical migration. Vertical migration, in my opinion, is a crucial component of the ocean's power plant.

In fact, a fish on your dinner plate very certainly consumed a vertically migrating organism.

Therefore, it benefits not only the health of the earth but also the provision of a vital food transmission mechanism for people.

I find it quite astonishing that the organisms in the ocean must consider the world in as many dimensions.

While in the water, place doesn't really exist, we're so used to being able to use our GPS and knowing that if we return to the same location, it will look the same.

You continue to follow the water packet as it is tossed around.

Additionally, if you tried to stay in one spot, the environment's qualities would alter radically over time.

Understanding the world that these animals live in and beginning to think like them are really difficult concepts to grasp.

When you say it out loud, it sounds pretty straightforward, but if we mess with the biggest migration on Earth—this enormous event that takes place every single night—we might seriously damage the world.

We might even commit suicide in the end.

I apologize.

Stay inquisitive.

Actually, you're welcome; I'm not sorry.

Hello everyone, this program was a part of PBS's celebration of Earth Month.

You regarded Earth Day as positive.

We still have a whole month, and I'd want to inform you about the new "Untold Earth" series that will air on PBS Terra.

The program, which is a collaboration between Atlas Obscura and PBS Nature, explores the mysteries of some of North America's most bizarre and extraordinary natural wonders.