How profound is the ocean? What Lives Deep in the Ocean?

All right, who's got a good pile of thalassophobia here? If there's nothing you know about the deep sea, you're about to get a healthy pile of it. You should know that we've only been exploring 10% of the ocean, meaning that there's an absolute mess of things that we have yet to know about our own world. If you go far enough, you should also realize that no sunlight or food makes it far enough down into the water. Which would mean that life is difficult there, and that if things were alive, they would be small. But some stuff is heavy. Like, 33 feet and 1,500 pounds of large squid. How do deep sea animals get so large with so little food and light? And anyway, how big is the ocean?

And if you're interested, also find out: How Deep is the Deepest Hole in the World?

Deep The Challenger

Have you ever glanced down while swimming, only to find that you can't see the bottom of the pool, the lake, or some part of the ocean you're in? You are smarter than any of us, if that doesn't fill you with an overwhelming sense of fear and dread. They tell you, at least in a tub, how big this thing is.

True, at least we know how deep the ocean can get, sort of. But you're probably not going to like how far it gets, unfortunately.

The Titanic was located about 2.4 miles below the surface, for perspective (about 3.8 km). It's pretty deep, huh? Like, it's already pitch black by that point.

Except the deepest part of the ocean we’ve made it to is Deep The Challenger, a point near the southern end of the Mariana Trench in the Pacific Ocean. It’s so deep less people have been down there than we’ve sent to the Moon. How deep is “less people than the Moon” you might ask? 6.8 miles (11 km) deep. That’s deeper than Mount Everest is tall (5.5 miles, 8.9 km)!

Deep Ocean Zoning

What the layperson thinks of as the ocean generally falls under the epipelagic zone. It only goes down about 650 feet (0.2 km). Which is like 2% of Deep The Challenger. Colloquially, it’s referred to as the “sunlight zone,” since this is almost the limit of the Sun’s reach.

You have reached the Mesopelagic Zone because you have passed through the sunlight. This will take you to about 3,300 feet (1 km) deep from the bottom of the sunlight field. The sunlight is pretty dim by this point, so you're going to start seeing those fun and funky flickering fish. "They term this the "twilight zone" fittingly. You haven't reached another world physically, but it may as well be one.

The appropriately named midnight zone, also known as the bathypelagic zone, occurs past the twilight zone. You're going to make it down to 4 km (13,000 feet), and you're not going to see sunlight at all. The only light you'll see is from bioluminescent animals, or flashlights of your own. Since it's dark, much of the life you'll see is black or red, because if no one can see you, there's no need to be colorful. Yeah, if you're wondering why the color of preference is red, that's because red is the longest wavelength in the visible spectrum, so it's the simplest to dissipate. It's practically black for fish purposes.

We've got to go deeper...

The Abyssopelagic Zone (the "abyssal zone") takes us down to about 19,500 feet in existential crisis time (6 km). Thanks to the pressure, the majority of life here is invertebrate, and the water temperature is practically freezing.

But it goes deeper, to the hadalpelagic zone. Here we’ve just got… The bottoms of the trenches. They take us to the deepest parts of our ocean trenches, like Deep The Challenger. By this point, the water pressure is 8 tons per square inch. That’s literally like being crushed by 48 Boeing 747 jets from all directions at once. Surprisingly, and perhaps miraculously, we’ve found life even down here.

Honestly, short side note, there's no way Earth is the only planet with life on it if life is going to persist even here, right?

Unfortunately, we’ve found a little more than just life at the bottom of Deep The Challenger. We’ve also found plastic bags. So we guess pollution knows no bounds.

That's depressing. Dang.

Gigantism Deep-Sea

We can't taunt you in our intro with giant sea monsters and not speak a bit about them. It has been discovered by scientists that certain deep sea creatures can get tall. Like big, dumb. We described the 1,500-pound, 33-foot-long beast known as the colossal squid. Since squids aren't frightening enough anymore. And yes, the colossal squid is bigger than the giant squid that is sometimes mentioned. So the Kraken, essentially, is true.

Anyway, at very high pressures, deep sea creatures exist (see that Boeing 747 thing we mentioned earlier in this post). Because of this strain, there are usually no skeletons for big creatures because, well, they'd be crushed.

We also know that food this far down in the ocean is super scarce, so you'd think a lot of species this far down would be weak. Smaller bodies mean that to support themselves, they need less food, right?

Incorrect. Well, in truth, right, but just kind of. We can thank Kleiber's Rule, which basically means that larger animals have metabolisms that are more efficient. Essentially, big things need a lot less to eat. It is also observed that giant isopods in captivity can go without food for 5 years in captivity. For 5 years!

Food storage is also there. Creatures of the deep sea, like a giant isopod, eat a lot of food when they get the chance. We're talking about so much food that they can practically no longer walk.

We should consider the relative absence of predators as well. Since there are so few other animals deep down in the abyss, as you are getting tall, nobody will be around to eat you. Then you get really fat, and nobody is big enough physically to eat you. Consequently, sea creatures.

Need more Giants of the Deep Sea? Around them, here's a quiz.