Featured Image: National Geographic
By: Eva Gruber
Over 60% of our planet is ocean that is more than a mile deep – this is the deep sea, where zero sunlight penetrates, temperatures can be near freezing, and pressures reach crushing power. More people have been in space than have visited this habitat, the biggest on our planet.
Located near the island of Guam in the western Pacific, the Mariana Trench is formed at the subduction of the Pacific oceanic plate beneath the Mariana plate. The crescent-shaped trench is about 2,550 km long and an average of 69 km wide.
It contains the deepest parts of the ocean, including Challenger Deep, the record of depth on our planet at nearly 7 miles deep. While thousands of people have climbed Everest, the highest peak on Earth, only two people have ever reached the deepest point. This is the hadopelagic zone, which extends from 6,000 meters to 11,000 meters deep.
Four descents into the Mariana Trench have been completed. The first was the US Navy-owned Trieste in 1960, and reached a depth of 35,814 ft. Following the first descent was the Japanese Kaiko in 1996 and Nereus in 2009.
The Canadian film director James Cameron built his own manned deep sea submersible and reached the bottom in 2012. In July of 2015, researchers at Oregon State dropped a titanium-encased hydrophone to record depths to record sounds within the Mariana Trench, and the project was so successful that they plan on repeating it in 2017 for an extended period of time.
Deep-sea sea cucumbers that grow larger than their shallow water cousins, holothurians are ecologically important animals of the deep sea benthos. Known for expelling their guts for protection, holothurians of the deep sea might also provide housing (inside their bodies) for other organisms much like their cousins upstairs do.
‘Supergiant’ Amphipod (Hirondellea gigas)
At up to two inches long, these amphipods are real giants compared to their close, well-known relative – the beachhopper. These amphipods live in swarms, opportunists scavenging for fallen organic matter, whalefalls, and even sunken wooden ships and plant matter.
Deep Sea Anglerfish (Melanocetus johnsonii)
It is the female that comes to mind when we think of this iconic deep sea species, as the male is a fraction of her size and exists simply to deliver sperm.
When a male finds a female in the void of the pelagic deep sea, he bites onto her, eventually becoming a part of her body permanently – much like a parasite. Deep sea anglerfish use a bioluminescent lure to find each other as well as lure in potential prey.
Sessile, gelatinous animals that anchor their bodies to the seafloor and sides of canyons, tunicates (also known as “sea squirts”) may look closely related to jellies, but they are actually more closely related to humans, as chordates (animals with dorsal nerve chords and notochords).
These deep-sea tunicates are of a special variety – predatory, they wait for organisms such as small fish or invertebrates to float or swim into its huge gulping hooded “mouth”.
Also know as rattails, grenadiers are slow-moving bony fish found at great depths, scavenging the bottom for organic matter to consume. They are protected from the crushing depth with a chemical called trimethylamine oxide (see the snailfish below), which allows their cells to function normally and maintain proper salt levels.
The high pressure would otherwise do some dangerous things to their cells and membranes. trimethylamine oxide is also what gives sea creatures that fishy smell, so deep sea fish often smell much fishier than their shallow water cousins.
Cartilaginous fish related to sharks and rays, chimaeras are also known as “ghost sharks”. Resembling sharks in some ways, they also have similar fertilization method, with the males using claspers to inseminate females. Male chimaeras also have a retractable sexual appendange on the front of their head.
Mysterious multinucleate single celled organisms that grow up to a whopping 20 centimeters in diameter (a single cell!), these deep sea organisms were recently classified as foramniferans, types of ameboid protists. Abundant in the deep sea (with local densities up to 2,000 per 100 square meters), they surely play an important role in the ecosystem – but as of yet very little is known about exactly what role they play.
A recent trip to the Mariana Trench, led by the University of Aberdeen, discovered the deepest-living fish – a new species of snailfish that breaks the record for any living vertebrate, found at 8,145 meters. The fish is still relatively new to science, but it is known to contain trimethylamine oxide, a chemical found in many deep-sea organisms which helps keep membranes and cell walls flexible so that the crushing pressure doesn’t kill them.
Due to the rigors and challenges of deep sea exploration, so much of that realm is a mystery to science. However, thanks to incredible modern technology we learn something new every time we descend to those depths, and marine biologists are continually surprised at the abundance of life.