What Lives in the Mariana Trench?

The Mariana Trench contains the deepest point in the ocean, known as the Challenger Deep. Part of the hadal zone, this alien world is home to unique aquatic species specially adapted for life in extreme cold, darkness and pressure. This article will focus on what lives in the deepest parts of the Mariana Trench. 

Where is the Mariana Trench?

It’s located in the western part of the Pacific Ocean, situated between the Philippines and Hawaii about 124 miles east of the Mariana Islands. It’s over 35,000 feet deep. The deepest regions of the ocean are termed the hadal zone, a reference to Hades, the Greek underworld. Therefore, the Mariana Trench is located in the hadal zone. 

No sunlight penetrates these depths. Consequently, the organisms that live in the hadal zone are often blind or have poor vision. Nutrients are scarce, and they usually come in the form of animal carcasses drifting down from shallower waters. Most animals living at these depths are scavengers or detritivores — organisms that eat decomposed plant and animal matter as well as feces. 

What lives in the Mariana Trench? 

Sea Cucumbers

These bizarre, boneless sea creatures resemble their namesake and are found on the ocean floor worldwide. They have a mouth surrounded by tentacles. Sea cucumbers possess the remarkable ability to flatten their body, allowing them to squeeze through small openings, and then reconstitute themselves into their original shape. 

These simple animals lack a brain, but they do have the ability to sense light and touch. They generally scavenge on plankton and decaying organic matter that falls to the seafloor. This makes sea cucumbers natural recyclers, much like the role that vultures play on land. 

Mariana Snailfish

Resembling a pale, slimy tadpole, the Mariana snailfish isn’t much to look at. It has transparent skin, thin muscles and enlarged organs, all of which help it survive at extreme depths. In fact, it may be the deepest fish ever caught, vying for this record against an eel and another species of deepwater fish. 

The snailfish appears to be almost or completely blind. It may be the top carnivore along parts of the Mariana Trench, eating small crustaceans and having seemingly no other predators to worry about. Researchers have found that the female’s eggs are relatively large compared to her body. 

Amphipods

Amphipods are crustaceans, a subphylum that also includes lobsters, crabs, shrimp and woodlice. One species that lives in the Mariana Trench can grow to a much larger size than the normal varieties that live in shallower water. This phenomenon is known as deep-sea gigantism, and it’s the same reason that giant squid and Japanese spider crabs are so enormous. 

Supergiant amphipods are usually scavengers, feeding on the carcasses of large animals that sink to the ocean floor. Others eat algae or prey on other small organisms. A 2019 study found that 100% of amphipods in the Mariana Trench had eaten plastic, with researchers finding it in the hindgut of every amphipod they examined. This means that microplastics have found their way to even the deepest parts of the ocean. 

Aphyonids

Not to be confused with amphipods, aphyonids are fishes. Did you know? A group of one species of fish can be referred to as fish, but several species in a group are called fishes. This indicates that multiple species are being discussed.

There are numerous genera — the plural of genus — of fishes in this family. Much like the Mariana snailfish, they resemble ghostly white tadpoles. They have gelatinous skin with no scales, and pale, bulging eyes. Aphyonids give birth to live young. 

They lack a swim bladder, which is an organ that helps keep fishes afloat. Their lack of a swim bladder makes it easier for them to stay deep underwater. 

Acorn Worms

Acorn worms look a little like smooth earthworms, with a proboscis, a fleshy collar and a long, cylindrical trunk forming the main part of their body. Many species eat sand and extract the decaying organic matter from it. They breathe through gill-like structures in a similar manner to fish. 

Researchers have found acorn worms in the family Torquaratoridae living in the Mariana Trench. They have gelatinous bodies and spend their time on the seafloor. 

Jellyfish

At least one species of jellyfish inhabits the dark, murky waters of the Mariana Trench. The yet-unnamed species has a clear, red-striped body with luminous yellow orbs inside, and possesses two sets of tentacles — one short and one long — for catching prey. Researchers discovered the jellyfish in 2016 and placed it in the genus Crossota, a genus of jellyfish that are widespread throughout the world. 

Jellyfish are the oldest multi-organ animal group. Evolving some 550 million years ago, they’re older than any other animal that has ever existed, excluding sponges. It’s hard to fathom just how old jellyfish are, but think of it like this: For 190 million years, there was a world with jellyfish, but no trees. 

Polychaetes

These flat-bodied marine worms vary in appearance and behavior depending on which family they belong to. They resemble centipedes and come in a bright array of colors, with multiple leg-like protrusions called parapodia covered in bristles. Tube worms and clam worms are examples of polychaetes.

During a 2020 expedition to the Mariana Trench, researchers discovered several new species of polychaete worms. They also found numerous plastic bags, electric wires and a single beer can on the deepest parts of the seafloor. 

It’s both fascinating and sad to speculate whose beer can made its way down to the Mariana Trench. What are the odds? In addition to discovering new marine species, the 2020 expedition showed that pollution is more pervasive than previously thought, and highlighted the importance of reducing single-use product consumption. 

Living in the Mariana Trench

Despite the challenging conditions, numerous species live in the deepest part of the ocean. They’re specially adapted to withstand darkness, intense water pressure and cold temperatures, and many lack eyesight or a swim bladder. Future expeditions to the Challenger Deep will surely uncover even more of these mysterious life forms that call the ocean floor their home.