Who lives here? Lots of plankton (tiny plants and animals that float, as shown); nekton (tiny plants and animals that swim); jellyfish; sea turtles (shown); a variety of fish including tuna (shown), marlin, salmon, and sharks; and cetaceans (dolphins and whales).
It’s not as though these zones are sectioned off like office cubicles. Plenty of animals roam freely from one zone to another. Animals that need to breathe air, such as sea turtles, dolphins, and whales generally hang out closer to the surface just so they can get their heads (or noses or blowholes) above water regularly. Others prefer the shallower water for other benefits, such as food, light, warmth, and lower water pressure.
Some animals in this zone have evolved the ability to produce their own light — a trait referred to as bioluminescence (creating light through biochemical processes). Instead of carrying a flashlight to find their way in the dark, they are the flashlight. Although scientists aren’t quite sure about the purpose of this superpower, they think it might be used to ward off or evade predators, detect or lure prey (ooh, shiny light!), or communicate with members of their own species.
Counter-illumination: Some sea creatures that can bio-luminate may use this skill as camouflage, illuminating their soft underbellies to blend in with light coming from the surface, while the tops of their bodies remain dark to blend in with the darkness below them. This application of bioluminescence, called counter-illumination, protects the creature from predators above and below. When predators from below look up, all they see is light. When predators from above look down, all they see is darkness. Take that, camo pants.Life starts to get a bit weird in this zone. Here, you’re likely to start bumping into cool fish like the lanternfish, hatchetfish, and barbeled dragonfish all of which can produce their own light. You can also find species of bristlemouths. These fish, generally no larger than your finger, are not only thought to be the most common fish in the ocean, but also the most common vertebrate on Earth — more abundant than humans, chickens, and rats combined. Let that sink in for a second. Some marine mammals and sharks can also be found here, but most will stay in the mesopelagic only for relatively short periods before returning to the surface. Swordfish, ctenophores (see below) and siphonophores (jellyfish relatives), and firefly squid are other interesting animals that can be found in this zone.
The creatures that live here are too insane to make up, but they’re not the most colorful — just about everything is black or red, which makes everything invisible in water at these depths. (Certain wavelengths are filtered by water faster than others. Because red light has the longest wavelength and is absorbed quickest, once you go deep enough, anything red appears black.)
If you cut yourself diving at around 60 feet deep, your red blood may appear purple and, if you go any deeper, even black. Of course, we’re not recommending that you poke your finger when you’re diving, but if you happen to suffer a small cut underwater at that depth and you’re looking for a cheap thrill . . . .Calling this zone their home are the weird and wonderful barreleye fish, giant isopods, viperfish, vampire squid, and anglerfish. Occasionally you can find sperm whales here, and if you’re really, really lucky, you can see one battling a giant squid (of course if you do, take a picture because no one has captured that epic battle on film yet). The deepest diving marine mammal, the Cuvier’s beaked whale, can also reach this zone. This elusive and strange-looking animal holds the record for the longest mammalian dive, plunging up to 3,500 meters (11,480 ft) deep (that’ll make your ears pop) in search of deep-water cephalopods and squid.
Many animals in this zone and deeper have adaptations to allow them to eat almost anything, including prey much larger than them. Gulper eels have specialized jaw structures that enable them to open their mouths incredibly wide. Sharks and their relatives, including the Greenland shark (which can live for 400 years), ghost shark, frilled shark and goblin shark can sometimes also be found in this zone, as well as the deepest living octopus, the dumbo octopus shown (although some say it can be found at even greater depths).
The gulper eel says ahh!
Dumbo Octopus isn’t she (or he) cute?
Generally, the further down you go, the fewer species you encounter, because these are tough environmental conditions to adapt to. Life here is thought to have changed little over millions of years. Some abyssal species include the common fangtooth, tripod fish shown (they’re hermaphroditic, meaning they have both male and female reproductive organs, which means they can produce young either with another fish or on their own!), hagfish, cusk eels, grenadiers, and viperfish. In some places, you can find deep sea-corals, which don’t need sunlight to survive.
The tripod fish.
Viperfish (Chauliodus sloani)—look at those teeth!!!
Deep-sea creatures must be able to tolerate intense pressure (from the weight of the water above), total darkness, and near freezing temperatures. That’s not to say that animals living closer to the surface have an easy life; they face a greater risk from predators and from changes in environmental conditions.
Life becomes very limited in this zone. You can find giant, single-celled xenophyophores, deep sea microbial mats, amphipods, sea cucumbers, jellyfish, and other invertebrates such as tube worms, decapods, bivalves, and sea-anemones. Species of snailfish, cusk eels, and eelpouts can also be found in this region but are limited to relatively shallow areas, and usually closer to the seafloor. And even though it is really hard for people to venture this far down, our trash manages to find a way — namely, our plastic. Yup, even here in the deepest part of the ocean, recent expeditions found a plastic bag at one of the deepest points of the Mariana trench, nearly 11 kilometers (about 7 miles) down. Ugh.
A sea cucumber.