Deep Sea Life: in the Deepest Trenches, Around Vents, New Species | Sea Life, Islands and Oceania

DEEP SEA LIFE

deep sea sea pig eating a crab

The deepest parts of the ocean trenches, up to 11 kilometers (seven miles) deep, are in the “Hadal zone”, named after the god of the underworld. This region is often referred to as an “abyss” Greek for “bottomless void” or “pit of hell”. Steven Poole writes in The Telegraph, “Down there, no sunlight can penetrate, and it used to be thought that below only 500 meters no life could survive at all, that most of the ocean was “azoic”: bereft of animal life. Now it turns out that it is all biosphere, and indeed that life might even have begun in the deep, around hot hydrothermal vents, where seawater that has leaked down through the Earth’s crust and been heated to beyond boiling point by the Earth’s magma erupts back into the ocean. Microbes discovered down there can survive being baked in an oven at 121 degrees Celsius (250 degrees F). [Source: Steven Poole, The Telegraph, March 13, 2021]

Pressure increases with ocean depth. At sea level, the air that surrounds us presses down on our bodies at 14.7 pounds per square inch. You don't feel it because the fluids in your body are pushing outward with the same force. Dive down into the ocean even a few feet, though, and a noticeable change occurs. You can feel an increase of pressure on your eardrums. This is due to an increase in hydrostatic pressure, the force per unit area exerted by a liquid on an object. The deeper you go under the sea, the greater the pressure of the water pushing down on you. For every 33 feet (10.06 meters) you go down, the pressure increases by one atmosphere. [Source: NOAA]

Many animals that live in the sea have no trouble at all with high pressure. Whales, for instance, can withstand dramatic pressure changes because their bodies are more flexible. Their ribs are bound by loose, bendable cartilage, which allows the rib cage to collapse at pressures that would easily snap our bones. A whale's lungs can also collapse safely under pressure, which keeps them from rupturing. This allows sperm whales to hunt for giant squid at depths of 7,000 feet or more.

Marine biologists can now observe deep ocean kilometers below the surface using camera-equipped remote-control submersible that can be operated from the relative safety of a boat above it. New species are discovered in the ocean each year by marine biologists and other ocean scientists. Many of these newly discovered species live deep on the ocean floor in unique habitats that depend on plate movement, underwater volcanoes, and cold water seeps.

Deepwater fish generally live longer than their shallow-water counterparts. Some stay alive for more than 100 years possibly because of a lack of predators, and slow rate of growth and reproduction.

Pompeii worms live near deep sea vents. Their tails can tolerate near boiling hot temperatures while their heads, just a few centimeters away, are adapted to deep-sea cold. Scientists thinks their circulate fluids through their bodies “like a natural heat pump.”

Websites and Resources: Animal Diversity Web (ADW) animaldiversity.org; National Oceanic and Atmospheric Administration (NOAA) noaa.gov; “Introduction to Physical Oceanography” by Robert Stewart , Texas A&M University, 2008 uv.es/hegigui/Kasper ; Fishbase fishbase.se ; Encyclopedia of Life eol.org ; Smithsonian Oceans Portal ocean.si.edu/ocean-life-ecosystems ; Woods Hole Oceanographic Institute whoi.edu ; Cousteau Society cousteau.org ; Monterey Bay Aquarium montereybayaquarium.org ; MarineBio marinebio.org/oceans/creatures

Book: “The Brilliant Abyss: Exploring the Majestic Hidden Life of the Deep Ocean, and the Looming Threat That Imperils It” by Helen Scales, a British marine biologist (Grove Atlantic, 2021),

Marine Snow and Whale Fall

Deep sea jelly Halicreas minimum

Marine snow is a shower of organic material falling from upper waters to the deep ocean. As plants and animals near the surface of the ocean die and decay, they fall toward the seafloor, just like leaves and decaying material fall onto a forest floor. In addition to dead animals and plants, marine snow also includes fecal matter, sand, soot, and other inorganic dust. The decaying material is referred to as “marine snow” because it looks a little bit like white fluffy bits. The “snowflakes” grow as they fall, some reaching several centimeters in diameter. Some flakes fall for weeks before finally reaching the ocean floor.[Source: NOAA]

This continuous rain of marine snow provides food for many deep-sea creatures. Many animals in the dark parts of the ocean filter marine snow from the water or scavenge it from the seabed. NOAA scientists and others have measured the amount of useable material in marine snow and found that there is plenty of carbon and nitrogen to feed many of the scavengers in the deep sea. The small percentage of material not consumed in shallower waters becomes incorporated into the muddy “ooze” blanketing the ocean floor, where it is further decomposed through biological activity. About three-quarters of the deep ocean floor is covered in this thick, smooth ooze. The ooze collects as much as six meters every million years.

When whales die and sink, their carcasses — known as whale falls — provide a bounty of nutrients for deepwater creatures. During a 2019 expedition, researchers discovered a whale fall at 3,238 meters (10,623 feet) below the surface near Davidson Seamount in NOAA's Monterey Bay National Marine Sanctuary. Different stages in the decomposition of a whale carcass support a succession of marine biological communities. Scavengers consume the soft tissue in a matter of months. Organic fragments, or detritus, enrich the sediments nearby for over a year.

The whale skeleton can support rich communities for years to decades, both as a hard substrate (or surface) for invertebrate colonization and as a source of sulfides from the decay of organic compounds of whale bones. Microbes live off of the energy released from these chemical reactions and form the basis of ecosystems for as long as the food source lasts. At deep sea levels this forms a new food web and provides energy to support single- and multi-cell organisms and sponges, thus adding to the ocean's food chain.

Strange Deep Sea Creatures

According to the Schmidt Ocean Institute the deepest sea creatures include amphipods, sea pigs (an echinoderm, or star fish) and various worms. A hadal sea pig observed in the 10,047-meter- (32,963-foot) -deep Kermadec Trench in May 2014 had “stubby walking "legs" and a ring of suction cups around its mouth for gathering dead organic material from the mud. Other deep sea creatures include, Steven Poole writes in The Telegraph, “luminous ctenophore (or comb jelly), looking like an extraterrestrial spaceship with glowing tentacles extended, or a red vampire squid, webbed fingers ready to grasp, resembling nothing so much as the facehugger from Alien. [Source: Steven Poole, The Telegraph, March 13, 2021]

“It is, indeed, weirdness all the way down.” The bestiary includes “the relatively familiar sperm whale, which can hunt a kilometer deep, to the worms that feed on its bones once they have fallen to the ocean floor, known — of course — as “bone-eating zombie worms”. We are also introduced to ultra-black deep-sea fish, cyborg snails that make their shells from iron, carnivorous sponges, and Yeti crabs that have furry claws: “Tipped with a pair of goofy-looking, rounded pincers,” the author explains, “these pelts of blonde fur give the animal the look of a deep-sea crab that might appear on The Muppet Show.” And that’s not to mention the three species of glow-in-the-dark sharks.

19th century depiction of life at 1,500 meters deep

Stephanie Pappas wrote in Live Science: Animals that hope to survive at the bottom of the sea have to do without light and stand up to the incredible pressure of thousands of meters of water. Famous residents include the blobfish, which looks fairly unassuming while swimming thousands of feet below the surface but deflates into a saggy sack when brought to the surface, where the pressure is 100 times less than what the fish is adapted to. [Source: Stephanie Pappas, Live Science, April 20, 2022]

Scientists are only beginning to catalog the other odd creatures at the ocean depths. Javier Sellanes López, a marine biologist at Catholic University of the North in Chile, has been exploring the seamounts off the coast of South America, turning up an array of new or poorly understood species. Take Eunice decolorhami, a polychaete worm found living in tubes 590 to 1,115 feet (180 to 340 m) deep on the slopes of the Desventuradas Islands and the seamounts of the Nazca Ridge. With what appears to be bulbous eyeballs and an underbite, these animals look more like background characters in "The Muppet Show" than marine worms. The researchers have also turned up samples of the eerie white-and-red crab Ebalia sculpta, a bottom dweller that scuttles amid tube worms and anemones about 650 feet (200 m) below the surface. "Its main distinguishing feature is a face carved into its cephalothorax [fused head and body] that resembles the image of an underworld being," Sellanes López told Live Science. In other words, it's a deviled crab.

But let's go deeper. Lisa Levin, a biological oceanographer at the Scripps Institution of Oceanography in California, nominated xenophyophores as one of her favorite strange deep-sea creatures. Xenophyophores are single-celled organisms called protozoans that clump together sediments to form elaborate houses called "tests." These tests look a bit like plants, corals or large lichens. They're found below about 1,300 feet (400 m) well into deep-ocean channels such as the Mariana Trench and, in this barren world, provide shelter for invertebrates and developing fish embryos, Levin told Live Science. The Viperfish is one of the toothy denizens of the deep. In her book “The Brilliant Abyss” Helen Scales one creature that is “a close relative of the woodlouse that hides under rocks or garden pots, but pale pink and the size of a rugby ball.” She is very good on the sublimely mountainous topography of the seabed, and the unimaginable forces that operate on its denizens. Once you are at a depth of 8km, she explains, where snailfish can live, the pressure exerted by all that seawater above is equivalent to “an elephant standing on every few square centimeters of your body”. Down there too we find scavenging crustaceans called amphipods: “They are supremely unfussy eaters and will devour anything that falls into a trench.” "I find the fact that a protozoan can make a home for invertebrates or provide nursery habitat for snailfish to be a delightful idea," Levin said.

Less delightful, perhaps, are bone-eating worms (Osedax), a deep-sea oddity suggested by Scripps Institution marine biologist Gregory Rouse. These feathery red worms eat without mouths or guts, instead excreting acid to break down bones of dead marine animals. Females grow to be about 1 inch (2.5 centimeters) long. Males are just one-twentieth of an inch (1 millimeter) long and live in jellylike tubes clinging to females, existing solely to fertilize the females' eggs.

Amphipods — Among the World’s Deepest Living Animals

Elizabeth Kolbert wrote in The New Yorker: “Small crustaceans known as amphipods have been collected from the very bottom of the Mariana Trench, almost thirty-six thousand feet down, where the pressure is so great that the animals’ shells, in theory at least, should dissolve. A team of Japanese scientists reported that one deep-dwelling amphipod, Hirondellea gigas, protects its shell by coating it in an aluminum-based gel, produced from metal that it extracts from seafloor mud. [Source: Elizabeth Kolbert, The New Yorker, June 14, 2021]

amphipod

Amphipods make up an order of crustaceans with no carapace and, for the most part, with laterally compressed bodies. Ranging in size from 1 to 340 millimeters (0.039 to 13 inches) and resembling shrimp, they are mostly scavengers, who eat detritus on the ocean floor. More than 9,900 amphipod species have been described so far but there is probably a lot more. They are mostly marine animals but there are hundreds of freshwater ones too. Sandhoppers such as Talitrus saltator are examples of ones that live on land. [Source: Wikipedia]

The largest recorded living amphipods — Alicella gigantea — were 28 centimeters (11 inches) long, and photographed at a depth of 5,300 meters (17,400 feet) in the Pacific Ocean. Pieces of Alicella gigantea. retrieved from the stomach of a black-footed albatross were estimated to from creatures 34 centimeters (13 inches) in length. Scientists observed more specimens of A. gigantea in the 10,047-meter- (32,963-foot) -deep Kermadec Trench near Samoa estimated to be 34.9 centimeters long. Some that were 27.8 centimeters long were collected..

Amphipods have been spotted in the Challenger Deep, the deepest known point in the ocean. Located in the western Pacific Ocean, at the southern end of the Mariana Trench, near the Mariana Islands, it is 10,902–10,929 meters (35,768–35,856 feet) deep. The University of Aberdeen’s Oceanlab videoed ones in the Mariana Trench at at a depth of 10,545 meters (34,597 feet) in December 2014. The Schmidt Ocean Institute’s SOI Rock Grabber Lander observed them around 10,668 meters (35,000 feet) in Sirena Deep, the world’s third deepest spot, also in the Mariana Trench south of Guam.

According to the Schmidt Ocean Institute: Amphipods thrive below 8000 meters, perhaps because there are no fish eating them. There are scavenger species that eat organic material from above, and predatory species that eat the scavengers. Why do these organisms thrive where fish dare not go? At the moment, we can’t say. If pressure is the key, perhaps these organisms have been evolving longer than fish and have more pressure-resistant proteins. There are hints. Scientists in Japan reported that a hadal Mariana amphipod has an enzyme that digests wood! Moreover, this enzyme (unlike many fish proteins) works better under pressure than it does at low pressure.

Might amphipods also have better piezolytes (compounds that stabilize proteins against high undersea pressures)? In amphipods collected from various depths on other expeditions, we found that the deepest species have high TMAO like snailfish (the deepest-living fish). But they are also high in other interesting molecules including glycerophosphorylcholine (GPC) and scyllo-inositol. Both are protective agents. GPC occurs at high levels in mammalian kidneys, where it protects your proteins from harmful effects of waste products. Scyllo-inositol is being tested to restore mis-folded brain proteins associated with Alzheimer’s Disease. Do these also protect proteins at high pressure?[Source: Schmidt Ocean Institute]

Bizarre Deep-Sea Creatures Found 2,500 Off of Australia

In November 2002, scientists announced they had discovered a menagerie of creepy deep sea creatures, including fish that walk on stilts and animals that appear to made of ooze, in two new marine parks located 2,500 kilometers (about 1,500 miles) off Australia's western coast. One of the leaders of the 2002 expedition, Tim O'Hara, senior curator of marine invertebrates at the Museums Victoria (MV), said: "We know the region is covered with massive seamounts formed during the dinosaur era and we know the region sits at a critical juncture between the Pacific and Indian Oceans. We are really excited about the prospect of discovering new species, perhaps even new branches of the tree of life, which until now have remained hidden beneath the waves in this unexplored region."[Source: Tessa Koumoundouros, Nature, November 4, 2022]

The creatures were found in the new marine park territories that protect 740,000 square kilometers (about 285,000 square miles) of ocean around Cocos Keeling and Christmas Islands. , researchers observed a dazzling array of winged fishes casting themselves into the air. Nature reported: Using sonar, teams on the research vessel (RV) Investigator mapped the seabed over 35 days of exploration on their 13,000 kilometer voyage, uncovering ancient sea mountains, volcanic cones, canyons and ridges. The extinct volcanoes formed 140 to 50 million years ago.

Model of wood fall succession on deep sea floor

The sonar revealed Cocos Keeling Islands were twin peaks of a massive sea mountain rising nearly 5,000 meters from the sea floor. A third submerged peak was also identified, 350 meters below sea level. The crew reported collecting a big treasure haul of species after sampling habitats with small trawl nets from 60 meters down to a depth of 5,500 meters below the surface. O'Hara estimates up to one-third of these species may be new to science. This includes a potentially new type of blind cusk eel, with loose, gooey see-through skin. "These fish have really reduced eyes. In fact, if you see the picture you'll find they're like little golden depressions in the skin. They've got really loose, flabby, gelatinous skin and they're incredibly rare," MV senior collections manager Dianne Bray told the Australian Broadcasting Corporation.

The teams also discovered a hermit crab using a deep-sea colonial zoanthid coral as its shell. These goopy soft corals tend to incorporate sand or other bits of materials that happen to be lying around to give themselves some structure — including crabs it would seem. Fancy sea cucumbers, plenty of sea stars and lots of sea snails also call this region home as do many other strangelings of the deep.

A joint Australian-New Zealand exploration of submarine habitats around Norfolk and Lord Howe islands in the Tasman Sea off of Australia and New Zealand in 2003 towed trawling gear along the ocean floor, at a depth of 1,200 meters and pulled up more than 100 new species of fish and invertebrates. Among them were sea cucumbers, gulper eels, fangtooths, coffinfish, prickly dogfish, viperfish, slickheads, giant sea spiders, corals, and the fossilized tooth of an extinct megalodon — a shark many times the size of the great white. Franz Lidze wrote: There were spookfish (part squid, part fountain pen), whose snouts were equipped with electrical receptors to detect hidden prey; sponges as tall as ten feet; and humpback anglerfish — also known as black devils — that use bacteria to emit light through the long stalks sprouting from their heads. [Source: Franz Lidz, Smithsonian magazine, November 2015]

Some Characteristics of the Bizarre Deep-Sea Creatures Found Off of Australia

Among the creatures found on the ocean floor and the seamounts off the Cocos (Keeling) Islands near Australia were the tribute spiderfish and the bony-eared assfish. According to Business Insider and Fox News: An unknown cusk eel spotted about five kilometers (three miles) below the surface had never been seen before and was new to science. The eel, which is blind and has gooey skin, gives birth to live young. Fish usually lay eggs that grow on rock faces or the sea bed. But, unusually, this fish's babies grow inside its belly and it gives birth to live young. Its skin is loose, transparent and gelatinous.[Source: Marianne Guenot, Business Insider, December 2, 2022; Fox News,, December 9, 2022]

The goofy-looking batfish is a deep-sea ray also known for being a formidable hunter Like many other deep-sea animals, the batfish uses light to lure its prey in the dark of the ocean. This fish's luminescent lure is on its snout. Another fish, called the stoplight loosejaw, attracts its prey using red and blue glowing lights near its eyes. It gets its name from its impressive lower jaw. The luminescent organs are called photophores.

Not all animals at the bottom of the sea floor are colorless, transparent or covered with lights. Scientists also found bright red starfish and vividly-colored squat lobster. The pancake sea urchin has poison-tipped spines and flattens out like a pancake when out of water.

Dianne Bray, Senior Collections Manager at the Museums Victoria Research Institute in Australia, told Fox Weather The tripod fish stands stationary on its three ray fins to feed. "Those amazing deep-sea fishes that stand high up off the seafloor on their long, thin fin rays and face into the current to feed. They're not only just hermaphrodites, they're simultaneous hermaphrodites. So they have a functional ovotestis, which is a pretty interesting reproductive strategy and a great one for life in the deep sea where animals are rare," continued Bray. "So maybe they only have to meet one other fish to mate." The fish have fully formed ovaries and testes complete with sperm. They can not inseminate themselves, but they can inseminate any other tripod fish.

Deep Seafloor Filled with Entire Branches of Life New to Science

Bases on DNA evidence, scientists say that nearly two-thirds of seafloor life has not been discovered yet. Patrick Pester wrote in Live Science: Researchers sequenced DNA from deep-sea sediments around the world and found that there is at least three times more life on the seafloor than there is higher up in the ocean. What's more, nearly two-thirds of that life has not been formally identified yet. "It's been known since the 1960s that species diversity is very high in the deep sea, so very high numbers of species," co-author Andrew Gooday, a deep-sea biologist and emeritus fellow at the National Oceanography Centre in England, told Live Science. "What was new about this study was that there was a lot of novel diversity at the higher taxonomic level." [Source: Patrick Pester, Livescience. February 5, 2022]

Macrofauna colonizing wood after one year at the sea floor - journal.pone.0053590.g003.png
Macrofauna colonizing wood after one year at the sea floor.
a) Xylophaga dorsalis, b) Idas modiolaeformis, c) Glycera noelae sp. nov. d) Cryptonome gen. nov. conclava, n. sp., e) Phascolosoma turnerae, f) Asterechinus elegans, g) Bathynectes piperitus, h) unidentified deep-sea fish, i, k) unidentified species of amphipods, l) unidentified species of Leptostracea. (Pictures h, g, f are courtesy of Ifremer, France (Medeco-2 expedition))

“The deep-ocean floor covers more than half of Earth's surface but is home to some of the least-studied ecosystems, according to the study. Previous research analyzed DNA collected through the water column, from above the ocean floor up to the surface, so this latest study sought to complete the picture and give a global view of biodiversity in the ocean by looking at seafloor DNA within deep-sea sediments.

“The research team sequenced DNA from 418 seafloor samples gathered from all the major oceanic basins between 2010 and 2016 and compared them with existing DNA data from the rest of the ocean, separating the known DNA of dead organisms that had sunk to the bottom from the DNA of organisms native to the seafloor. Rather than trying to identify individual species from the DNA, the team looked at what they called sequence variants, or different versions of DNA sequences, to discriminate between major groups of species, like families or orders. The findings were published Feb. 4 in the journal Science Advances(opens in new tab).

“Most of the seafloor DNA could not be assigned to a known group on the tree of life, meaning it belonged to undiscovered family, order or other taxonomic group. The team focused on eukaryotic DNA from small organisms. "We're talking about small animals less than a millimeter [0.04 inches] in size, and probably a lot of protozoans, a lot of single-celled organisms," Gooday said. Larger animals, such as octopuses, weren't sequenced, so the richness of deep-sea life is likely even greater than what the team found. Gooday noted that they also looked only at DNA contained within sediments and not rocky outcrops or other deep-sea niches where other organisms may be living.

“It's not altogether surprising that so much biodiversity lies deep beneath the ocean's surface. The seafloor is a more complex environment than the ocean above it, with microhabitats like deep coral reefs and underwater volcanoes for species to adapt to. "If you have a very uniform environment, then all species are exposed to the same habitat," Gooday said. "But if that habitat is divided into lots of microhabitats, then species can specialize."

The researchers also learned more about the role the deep ocean plays in the so-called biological pump, the process by which ocean organisms such as phytoplankton absorb carbon from the atmosphere near the surface and sink to the deep sea, where the carbon is sequestered in the sediments. The team could predict the strength of the pump based on the composition of DNA in the sediments, so the researchers now know some plankton communities play a greater role than others in absorbing carbon dioxide and regulating the climate.

Deep Sea 'Mushroom' May Be New Branch of Life

A bizarre mushroom-shaped sea animal collected from the deep sea in 1986 during a research cruise off Tasmania has defied classification and may be a new branch of life. Paul Rincon of the BBC writes: A team of scientists at the University of Copenhagen says the tiny organism does not fit into any of the known subdivisions of the animal kingdom. Such a situation has occurred only a handful of times in the last 100 years. The organisms are described in the academic journal Plos One. [Source: Paul Rincon, BBC, September 3, 2014]

“The authors of the article note several similarities with the bizarre and enigmatic soft-bodied life forms that lived between 635 and 540 million years ago — the span of Earth history known as the Ediacaran Period. These organisms, too, have proven difficult to categorise and some researchers have even suggested they were failed experiments in multi-cellular life.

“The authors of the paper recognise two new species of mushroom-shaped animal: Dendrogramma enigmatica and Dendrogramma discoides. Measuring only a few millimeters in size, the animals consist of a flattened disc and a stalk with a mouth on the end. During a scientific cruise in 1986, scientists collected organisms at water depths of 400 meters and 1,000 meters on the south-east Australian continental slope, near Tasmania. But the two types of mushroom-shaped organisms were recognised only recently, after sorting of the bulk samples collected during the expedition. Co-author Jorgen Olesen from the University of Copenhagen. told BBC News: "We think it belongs in the animal kingdom somewhere; the question is where."

“The system used to group every life form on Earth encompasses several levels, or taxonomic ranks. A domain is the highest taxonomic rank and below that is a kingdom. Traditionally, biologists have recognised five or six kingdoms, including animals, plants, fungi and bacteria. Kingdoms are divided into phyla, which are grouped according to similarities in general body plan. They resemble organisms from the Ediacaran Period, many of which were thought to be evolutionary dead-ends "What we can say about these organisms is that they do not belong with the bilateria," said Dr Olesen.

“Bilateria represents one of the most important animal groupings, whose members share bilateral symmetry (their bodies are divided vertically into left and right halves that mirror one another). Humans belong within this grouping. The new organisms are multicellular but mostly non-symmetrical, with a dense layer of gelatinous material between the outer skin cell and inner stomach cell layers. The researchers did find some similarities to other animal groupings, such as the Cnidaria — the phylum that comprises corals and jellyfish — and the Ctenophora, which includes the marine organisms known as comb jellies. But the new organisms did not fulfil all the criteria required for inclusion in either of those categories.

Dr Olesen said the new animals could either be a very early branch on the tree of life, or be intermediate between two different animal phyla. He conceded that they might eventually find their way into an existing group, because there was still so little known about Dendrogramma's biology. One way to resolve the question surrounding Dendrogramma's affinities would be to examine its DNA, but new specimens will need to be found. The original samples were first preserved in formaldehyde and later transferred to 80 percent alcohol, a mode of treatment that prevents analysis of genetic material. Accordingly, the team's paper in Plos One calls for researchers around the world to keep an eye out for other examples. "We published this paper in part as a cry for help," said Dr Olesen.

Creatures Around Hydrothermal Vents

Elizabeth Kolbert wrote in The New Yorker: “Some of the seas’ most extraordinary animals live around hydrothermal vents — the oceanic equivalents of hot springs. Through cracks in the seafloor, water comes in contact with the earth’s magma; the process leaves it superheated and loaded with dissolved minerals. (At some vents, the water reaches a temperature of more than seven hundred degrees.) As the water rises and cools, the minerals precipitate out to form crenellated, castlelike structures. Hydrothermal vents had been theorized about for many years but remained unseen until 1977, when a team of geologists and geochemists travelling on a research vessel called the Knorr located one about two hundred and fifty miles northeast of the Galápagos. A pair of scientists went down to take a look at it in a submersible named Alvin. “Isn’t the deep ocean supposed to be like a desert?” one of them asked over Alvin’s phone link. “Yes,” came the answer from the Knorr. “Well, there’s all these animals down here.” [Source: Elizabeth Kolbert, The New Yorker, June 14, 2021]

“As Helen Scales, a British marine biologist, explains in her new book, “The Brilliant Abyss: Exploring the Majestic Hidden Life of the Deep Ocean, and the Looming Threat That Imperils It” (Grove Atlantic), “these animals” turned out to be fundamentally different from other creatures. At the bottom of the vents’ food chains are microbes that have come up with their own novel survival strategy. Instead of using photosynthesis, which harnesses the energy of photons, they rely on chemosynthesis, which uses the energy stored in chemical bonds. Since the late nineteen-seventies, Scales reports, researchers have catalogued hundreds of strange species living around vents; they include creatures so puzzling that it’s hard to find a limb for them on the tree of life.

“Yeti crabs, first observed in 2005 on a vent system along the Pacific-Antarctic Ridge, south of Easter Island, look like hairy white lobsters. Their “hairs” are actually extensions of their shells, and along them live colonies of chemosynthetic bacteria, which the crabs scrape up and consume. Yeti crabs were found to be so evolutionarily distinctive that taxonomists had to create not just a new genus but a whole new family for them.

“Xenoturbella profunda is a creature that looks like a discarded tube sock. First collected from a vent system in the Gulf of California in 2015, it has no intestines or central nervous system, and scientists aren’t even sure what phylum it belongs to. Chrysomallon squamiferum, commonly referred to as the scaly-foot snail, is a mollusk that’s been found at vents in the Indian Ocean, at a depth of ten thousand feet. It’s the only animal known to build its shell with iron, and around its foot it sports a fringe of iron plates that looks a bit like a flamenco skirt. The snail carries around chemosynthesizing microbes in a special pouch in its throat. In 2019, Chrysomallon squamiferum became the first vent-dwelling creature to be included on the Red List of Threatened Species, maintained by the International Union for Conservation of Nature. The rationale for the listing is that the species has been found at only three sites, and two of these are being explored for mining. Its living space, the I.U.C.N. has observed, is thus apt to be “severely reduced or destroyed.”

Creatures in the Deepest Trenches

Describing work of her team in the Marianas Trench, Mackenzie Gerringer wrote: “To humans” deep trenches “are harsh, extreme environments. Pressure is as high as 15,000 pounds per square inch — equivalent to a large elephant standing on your thumb, and 1,100 times greater than atmospheric pressure at sea level. Water temperatures are as low as 33 degrees Fahrenheit (1 degree Celsius). Yet, a host of animals thrive under these conditions. [Source: Mackenzie Gerringer, Postdoctoral Researcher, University of Washington, February 1, 2018]

Our team put down cameras baited with mackerel to attract mobile animals in the trench. At shallower depths, from approximately 16,000 to 21,000 feet (5,000-6,500 meters) on the abyssal plain, we saw large fish such as rattails, cusk eels and eel pouts. At the upper edges of the trench, below 21,000 feet, we found decapod shrimp, supergiant amphipods (swimming crustaceans), and small pink snailfish. This newly discovered species of snailfish that lives to near 27,000 feet (8,200 meters), is now the world’s deepest living fish.

At the trench’s greatest depths, near 36,000 feet (11,000 meters), we saw only large swarms of small scavenging amphipods, which are somewhat similar to garden pill bugs. Amphipods live all over the ocean but are highly abundant in trenches. The Mariana snailfish that we filmed were eating these amphipods, which make up most of their diet.

Describing creatures found living at a depth of 7,000 meters in the Peru-Chile trench of the South East Pacific Ocean, Hilary Duncanson wrote in The Independent: A “new type of snailfish was found ...A species of cusk-eel known as Ophidiids also gathered at our camera and began a feeding frenzy that lasted 22 hours — the entire duration of the deployment. Further research needs to be conducted to decipher whether this is also an entirely new species of cusk-eel that we have discovered. Our investigations also revealed a species of crustacean scavengers — known as amphipods — which we previously did not know existed at these depths in such great numbers. These are large shrimp-like creatures of which one particular group, called Eurythenes, were generally far larger and occurred much deeper in this trench than has ever been found before."Dr Toyonobu Fujii, a deep-sea fish expert from Aberdeen University, added: "How deep fish can live has long been an intriguing question and the results from this expedition have provided deeper insight into our understanding of the global distribution of fish in the oceans."

Image Sources: Wikimedia Commons; YouTube, Animal Diversity Web, NOAA

Text Sources: Animal Diversity Web (ADW) animaldiversity.org; National Oceanic and Atmospheric Administration (NOAA) noaa.gov; Wikipedia, National Geographic, Live Science, BBC, Smithsonian, New York Times, Washington Post, Los Angeles Times, The New Yorker, Reuters, Associated Press, Lonely Planet Guides and various books and other publications.

Last Updated March 2023