At the surface, each of those cups was 90% air and 10% tiny polystyrene beads. After each cup is artistically adorned with deep-sea imagery, they take a plunge to the abyss. At the crushing pressures of the depths, the air is squeezed out, leaving only those tiny polystyrene beads, and each cup becomes a miniature of its former self. One of the most extreme environmental gradients is the increase of pressure with increasing depth, starting at 1 atmosphere at the surface and reaching well over 1,000 atmospheres in the deepest parts of the ocean. How do organisms survive this great pressure, and what happens to them when they are brought to the surface?

The highest known pressure in the deep oceans coincides with the maximum known depth at the southern end of the Mariana Trench, the Challenger Deep. The actual maximum depth of Challenger Deep is disputed. The deepest reported measurement was by a Russian research vessel at 11,034 meters. The International Hydrographic Organization adopted 10,924 meters in 1993, but a subsequent 2010 survey, the most accurate to date, places the depth at 10,984 meters—25 meters greater. With every 10 meters corresponding to 1 atmosphere of pressure, this places the maximum known pressures in the deep between 1092.4 and 1103.4 atmospheres (110.7–111.8 MPa). Notably, several other deep-sea trenches—Tonga, Philippines, Kuril-Kamchatka, and Kermadec—in the Pacific Ocean also reach depths greater than 10,000 meters. In the Atlantic Ocean, the two deepest trenches are the Puerto Rico Trench at 8,800 meters and the South Sandwich Trench at 8,428 meters.

Exploring the depths of the ocean reveals a fascinating array of life forms, showcasing the incredible adaptability of both prokaryotic and eukaryotic organisms to high-pressure environments. Even in the Challenger Deep, where pressures exceed 110 MPa, microbial life thrives. Interestingly, several large multicellular organisms have been discovered at these extreme depths. A striking 74% of species found below 7,000 meters are endemic to these very deep areas. Among these invertebrates are the sea cucumber Myriotrochus bruuni, which inhabits the Mariana Trench at 10,710 meters, and the amphipod Hirondellea gigas, one of the most abundant creatures in the Challenger Deep at 10,897 meters. The hadal snailfish Pseudoliparis swirei holds the record for the deepest known vertebrate, living at an astonishing 7,966 meters.

How do organisms survive this depth? In short, there is a host of remarkable physiological and biochemical strategies that allow organisms to survive and thrive under the immense pressures found in the ocean’s depths. These adaptations include unique cellular structures and molecular mechanisms that confer resilience to high-pressure environments, such as specialized cell membranes, pressure-resistant enzymes, and unique protein folding techniques.

As you may remember from high school or college biology, a cellular membrane consists of a lipid bilayer. The structure is maintained entirely by the interaction of charges (or lack thereof) between water and the phospholipids. This makes the membrane semipermeable, much like a layer of oil on water. Extreme pressure results in tighter packing of the phospholipids, which lowers the permeability of the membrane. One adaptation by deep-sea animals to increase cellular permeability is to increase the percentage of unsaturated fatty acids. In a saturated fatty acid, all the carbons in the chain are linked by single covalent bonds. As you recall, a carbon can form four chemical bonds. If all these bonds are covalent (single), then a carbon could potentially attach to four other atoms. The term “saturated” comes from the fact that the carbon chain is loaded with hydrogens. If a carbon forms a double bond with another atom, it would bond with one less hydrogen. Thus, an unsaturated fatty acid has double bonds and is not “saturated” with hydrogens. The double covalent bond between adjacent carbons in an unsaturated fatty acid leads to a kink in the tails of the molecule. Thus increasing their concentration in the membrane leads to looser packing.

Pressure also selects for different enzymes. Changes in protein structure can influence their cellular function. Selection for rigidity is needed to counteract pressure and the resulting warping of proteins. Proteins contain hydrogen and disulfide bonds between different subunits and parts of the amino acid chain that dictate structure. Selection for proteins with increased bonding minimizes changes in shape due to pressure. Pressure can even make molecules more (or less) toxic. Urea is a good example: it becomes far more toxic as pressure increases. Deep-sea sharks, which like all sharks have a lot of urea in their blood, also have more of the protective chemical TMAO to offset this effect than their shallow-water cousins.

Pressure also does not favor air-filled volumes and sacs. The deepest diving submersibles require titanium spheres to hold the air-filled volume for their human inhabitants. For deep-sea animals, titanium is not an option, so most avoid having air-filled sacs. For example, deep-sea fish lack swim bladders. Other deep-diving animals like whales and seals have collapsible lungs to deal with extreme pressure (not to mention a whole host of other adaptations)!”

The post How Life Thrives Under the Ocean’s Crushing Pressure first appeared on Deep Sea News.

We fly along the shoreline and notice dozens of dead urchins.  The brine’s high density, which prevents it from mixing with the ocean above, also means that oxygen is not mixed in, creating an anoxic deathtrap for unsuspecting respiring organisms.  As we continue to explore, a small, semi-submerged mound in the middle of the brine pool begins to pulse and vent.  As we maneuver the Global Explorer closer, we see hundreds of cavities all venting fluid.  We take a sample of mud around one of these pits, in hopes of capturing its invertebrate builder.  Later on board the vessel, we examine the sample and discover a type of worm, a sipunculid, half the size of hot-dog with the bright green, gold, and purple colors. Students in my research group begin almost immediately referring to it as the Mardi Gras Worm.  How can this worm survive in such a toxic place?

Both cold seeps and their chemical and geological relatives, hydrothermal vents, are rich in reduced chemicals, particularly hydrogen sulfide.  These chemicals are toxic.  Sulfide and oxygen don’t naturally coexist for long because they react spontaneously and rather aggressively. However, this sulfide also provides a unique energy source, by willingly donating electrons, to chemosynthetic microbial live. These microbes use this to fix carbon and produce food. This makes vents and seeps different than the rest of the deep in being largely independent of sunlight and the photic zone above.  Many organisms in these environments either feed on free-living bacteria or form symbiotic relationships with chemosynthetic bacteria to obtain their food. This makes life challenging for both microbes and the animals that depend on them, as they need both sulfide and oxygen.

Despite these harsh conditions, these unique ecosystems flourish, showcasing the remarkable adaptability of life in extreme environments.  The hydrothermal vent worms, the Alvinellids, build tubes projecting from chimney walls, giving their gills access to oxygen-rich water.  The other end of the tube can then access the vent fluids rich in hydrogen suflide.  Mobile predators like the crab, Bythograea thermydron can move between areas with and without oxygen. Ice worms, so names because they are found on methane ice in the cold seeps of the Gulf of Mexico, circulate oxygenated water around itself using its bristle-bearing appendages. The adaptations extend well into the biochemical level.  The massive vent worm, Riftia pachyptila and the Alvnellids contain hemoglobins, giving them bright red colors, which bind insistently to oxygen.

But once dealing with oxygen issue, how do these species survive the toxic sulfide and heavy metal soup of vents and seeps. One way means of survival for these organisms is prevent sulfide from even reaching sensitive tissues.  Creating sulfide barriers may mean creating thick tubes or cuticles to prevent the skin from encountering suflide. For example, the Pompeii worm, Alvinella pompejana, at hydrothermal vents secretes proteinaceous tube that it shares with bacteria. Animals that inhabit chemosynthetic habitats also often possess a specialized blood protein that binds to sulfide—forever—preventing it from mucking up the business of respiring oxygen.  At hydrothermal vents, metals reach such high concentrations they precipitate out of water.   These heavy metal solids form the impressive chimney structures of vents and even coat the tubeworm tubes and the shells of snails and clams.  Chemosynthetic organism have ways of dealing with this too.  Special metal-binding proteins, called metallothioneins, grab toxic metals and even grouping together to form little bodies or particles distinct from the rest of the cell. These consolidated and enclosed heavy metals then stay out of the way and do not gum of the cellular works.

Overall, the exploration of these deep-sea ecosystems reveals the astonishing resilience and adaptability of life in extreme conditions, offering valuable insights into the limits of biological diversity and the potential for life beyond Earth.

The post Surviving Toxic Havens first appeared on Deep Sea News.

When whales die and sink to their watery graves, they bring to the seafloor bones rich in those fatty lipids. Thousands of bone-eating females, each just few millimeters high, will infest a whale carcass. So many will accumulate, the whale bones will appear to be covered in a circa 1970’s red shag rug-a rug that eats bones, has harems, and secretes acids, but otherwise a normal shag rug.  Originally, and with good reason, it was thought that Osedax was clearly a whale-fall specialist. The core of whale bones consists of a matrix rich in lipids – up to 60 percent.

But what about something wholly different?  Before the age of large marine mammals, large marine reptiles dominated the oceans. During the Mesozoic Era, rising to dominance in the Triassic and Jurassic periods, ichthyosaurs, plesiosaurs, and nothosaurs represented a diverse group of large marine predators terrorizing smaller creatures in the dark depths. The ichthyosaur Shonisaurus may have reached lengths of up to 21 meters in the Late Jurassic and Plesiosaurus may been 12–15 meters in length. The ancient sunken carcasses of these massive marine reptiles may have hosted ancient Osedax. We do know that prehistoric ichthyosaur falls are known to support communities similar to modern whale falls. 

Not to be outdone by other scientists in throwing random things on the seafloor to see what will eat it, in early 2019 I placed not one but three dead alligators on the seafloor in the deep Gulf of Mexico.  Alligators are nice modern analogues of the giant reptiles that once lurked in paleo-oceans and in my current state of Louisiana…well…readily available. And because we could, we place a packet of cow bones down there as well. 53 days later, my team and I visit the alligator carcass to find nothing but bones.  The reddish hue of fuzziness on them indicates Osedax are present.  On May 3, 2019, we overnight some of the collected bones out to California so Greg Rouse can inspect them in his lab and confirm their presence.  We wait patiently for an email from Greg.  On May 23, we get an email from him with the subject “Two new species :-)”. We are elated! Indeed, he finds females with well-developed ovaries and eggs.  Using genetics, he determines that the Osedax on the alligator and cow bones are both new species, previously unknown to science.

Fast forward to today when I get an email with the subject “Your species”. That Osedax from the alligator is named after me.

Osedax craigmcclaini n. sp. is named for Dr. Craig McClain, an esteemed deep-sea biologist and colleague who led the experimental alligator fall project (McClain et al., 2019) and provided the Osedax specimens for this study.

New Species of Osedax (Siboglinidae: Annelida) from New Zealand and the Gulf of Mexico

The post Introducing a New Species: My Namesake, a New Bone-Eating Worm first appeared on Deep Sea News.

Enter Simoniteuthis michaelyi, a newfound taxon that has captured the attention of researchers worldwide. This remarkable creature, based on a nearly complete pen accompanied by a head-arm complex, is a brilliantly preserved fossil.

What makes Simoniteuthis truly intriguing is its unusual arm crown, boasting only four arm pairs instead of the expected five. This anomaly challenges our understanding of vampyromorph anatomy.

But the surprises don’t end there. Examination of the specimen’s mouth region reveals evidence of predation on two bony fishes. The two animals died in the act of predation, i.e. one had caught the other and had begun to nibble on it, when they possibly sank into hypoxic waters and suffocated.

Unlike its modern descendant, Vampyroteuthis infernalis, Simoniteuthis inhabited shallower waters, reminiscent of Mesozoic vampyromorphs. This divergence in habitat and hunting behavior offers valuable insights into the evolutionary trajectory of these captivating creatures.

Through meticulous analysis of the fossil record, researchers speculate that vampyromorphs began a vertical migration into deeper waters, possibly driven by shifts in feeding behavior, as early as the Oligocene epoch.

Fuchs, Dirk, Robert Weis, and Ben Thuy. “Simoniteuthis, a new vampyromorph coleoid with prey in its arms from the Early Jurassic of Luxembourg.” Swiss Journal of Palaeontology 143.1 (2024): 1-10.

The post Ancient Origins of the Vampire Squid first appeared on Deep Sea News.

In the profound darkness of the ocean’s depths, organisms face a choice concerning their visual capabilities. Some species evolve specialized eyes that grow to astonishing sizes, as seen in creatures like the giant squid or owl fish. Alternatively, there’s the option to abandon the concept of eyes altogether. It’s the latter scenario that introduces us to an intriguing case: the “blind lobsters,” a peculiar group of 38 lobster-like crustaceans known as Polychelidae. These creatures exclusively inhabit the deep sea, dwelling at depths exceeding 5,000 meters (16,000 feet). Members of this group typically exhibit either absent or vestigial eyes, along with reduced or entirely absent eye stalks.

However, their lack of eyesight isn’t the most remarkable aspect of these creatures. Unlike typical lobsters, which possess two claws, Polychelids boast up to 5 pairs of claws. They feature two larger claws, followed by four smaller yet equally intimidating ones. The name of the group, “Polycheles,” derives from the Greek words meaning “many-clawed.”

While one might assume scientists are primarily intrigued by the blind, multi-clawed nature of these creatures. But they are complex. Scientists and Poychelids alike.  Polychelid bodies provide evidence of a transition from shrimp-like to lobster-like forms. Despite their lobster-like appearance, they lack certain primitive characteristics, such as a pointed telson (back-end) instead of the rounded telson found in typical lobsters. This appearance is similar to another group of unusual crustaceans, Eryon, dating back to the Jurassic and thus making Polychelids somewhat of a living fossil similar to the Coelacanths.  Yet intriguingly Eryon dwelled in the warm shallow seas of the Jurrassic.  The question of why they migrated to the deep sea remained unanswered—did they seek refuge in these depths, as suggested for other deep-sea taxa? Recent fossil and genetic evidence suggests that they have always inhabited these depths since their evolutionary origins in the middle Jurassic period.

Chang, Su-Ching, Shane T. Ahyong, and Ling-Ming Tsang. “Molecular phylogeny of deep-sea blind lobsters of the family Polychelidae (Decapoda: Polychelida), with implications for the origin and evolution of these “living fossils”.” Molecular Phylogenetics and Evolution 192 (2024): 107998.

Bezerra, Luis Ernesto Arruda, and Felipe Bezerra Ribeiro. “Primitive decapods from the deep sea: first record of blind lobsters (Crustacea: Decapoda: Polychelidae) in northeastern Brazil.” Nauplius 23 (2015): 125-131.

The post The Many Clawed, Blind Lobsters of the Deep first appeared on Deep Sea News.

In this luminescent tapestry, sea cucumbers emerge as unexpected stars. While we might not associate these echinoderms with bioluminescence, they contribute significantly to the underwater light show. Interestingly, in shallow waters, only a mere 1% of species can emit light, whereas the seafloor teems with bioluminescent activity, showcasing the radiant abilities of over 50% of its inhabitants. Venture to the depths of one kilometer, and you’ll find that luminous sea cucumbers constitute an astonishing 99% of all sea cucumbers.

Research by Manabu Bessho-Uehara, Jerrome Mallefet, and Steven Haddock have cast light on the bioluminescent secrets of sea cucumbers. Documenting not only 42 known species of glowing sea cucumbers but also six independent evolutions of bioluminescence within the sea cucumber lineage. The earliest illuminated sea cucumber may have been nearly 400 million years to the Devonian era, coinciding with the establishment of the first land animals.

While the precise details of how sea cucumbers produce their blue to greenish bioluminescence remain a mystery, the process involves a small organic compound known as luciferin. This compound is catalyzed to oxidize by an enzyme fittingly named luciferase.

The question of why sea cucumbers, or holothurians, need bioluminescence remains unanswered. Like other organisms that exhibit this phenomenon, the glow may serve various purposes. From communication to startling, misdirecting, and warning predators, to attracting, stunning, or illuminating prey, and even facilitating mate recognition—the role of bioluminescence in sea cucumbers raises intriguing hypotheses. One such theory suggests that it functions as a burglar alarm, attracting larger predators to deter potential threats—a fascinating manifestation of the age-old adage, “the enemy of my friend is my friend.”

Photos from : Bessho-Uehara, Manabu, Jérôme Mallefet, and Steven HD Haddock. “Glowing sea cucumbers: Bioluminescence in the Holothuroidea.” The world of sea cucumbers. Academic Press, 2024. 361-375

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The fossil record hints at a trend of shallow origins diversifying into the depths for certain marine organisms. However, conflicting results arise from approaches based on genetics, some supporting an onshore-offshore evolutionary pattern while others propose the opposite.

Enter the world of scleractinian corals, the stony or hard corals, a perfect testing ground for studying biodiversity across massive depth gradients. These corals span a wide depth range, from the ocean’s surface to depths surpassing 6,000 meters. How these creatures spread and settle in different areas, influenced by changes in their physical traits, help us understand the complex ways they’ve evolved over time and in response to the deep sea Take Micrabaciidae, a family of scleractinian corals. They have a slender, porous skeleton covered entirely by tissue—a probable adjustment for survival in the deep sea, where crafting a larger, sturdier skeleton becomes challenging due to lower aragonite, a form of calcium carbonate needed to build shells and skeletons, levels.

Half of the scleractinian corals form vibrant shallow reefs, while the other half, independent of the photic zone, thrives in cold waters across diverse regions and depths. This diversity not only paints a vivid picture of the coral world but also holds keys to understanding the origins of deep-sea life and diversity.

A new study by Campoy et al asks four key hypotheses about evolution of scleractinian corals

1. Origin of these corals might trace back to the upper bathyal zone (200–1000 meters). The steep and varied nature of this zone creates distinct environmental conditions, potentially fostering diverse adaptations across depths and serving as a catalyst for biodiversity
2. Lineages where symbiosis or coloniality emerged saw heightened rates of colonization. If these traits indeed bolstered the corals’ ability to spread, their emergence should align with faster colonization rates.
3. A prolonged evolutionary trend favoring faster colonization toward shallower waters. This hypothesis assumes that the common ancestor of these corals lacked symbiotic relationships and lived solitarily, suggesting that symbiosis inherently links to the sunlit zones, with colonial species generally occupying shallower depths compared to solitary ones.
4. Evolutionary forces predominantly shaping species’ depth ranges occur more significantly in shallower waters. As depth increases, environmental variability and interactions among species decrease, potentially slowing down the evolutionary pace through deeper zones.

The intricate dance of evolution (too much?) reveals itself through deep-water origins, surviving multiple geological changes and even global anoxic events. Specifically, the results show that the order Scleractinia originated 415.8 million years ago somewhere between 229–2287 meters depth. The emergence of the Scleractinia order in the deep sea aligns with a pattern of evolution from offshore to onshore and not providing strong support for upper bathyal zone origination as in hypothesis one. However, various coral lineages spread and settled at varying rates across different depths. Moreover, the pace of colonization slows at greater depths, underscoring the vulnerability of these ecosystems to further and current human exploitation.

Campoy, Ana N., et al. “Deep-sea origin and depth colonization associated with phenotypic innovations in scleractinian corals.” Nature Communications 14.1 (2023): 7458.

The post From Depths Unknown: Deciphering the Origins of Deep-Sea Biodiversity first appeared on Deep Sea News.

The above photo is of Apolemia lanosa a type of siphonophore belonging to phylum Cnidaria that also includes corals and jellies.  It’s basically the ocean’s way of celebrating Christmas all year long.  Like many other Cnidarians, siphonophores bud new individuals—exact clones themselves.  In a manner similar to Christmas elves although this is not proven by science. In the case of some Cnidarians, the clones never leave home so family never has to travel for the holidays.  

In some Cnidarians, clones in the colony will specialize but among siphonophores the specialization is unrivaled. Clones will specialize for feeding, defense, locomotion or reproduction. The feeding clones catch food by tentacles equipped with cells that shoot out poisonous harpoons stinging and stunning their prey.  In the most popular of all siphonophores, the Portuguese man o’ war, with a large gas filled buoyant bladder adapted for catching the wind and sailing.  Interestingly, all the clones are attached via a single digestive and circulatory system.  Research is still needed on which clones are adapted for drinking eggnog, singing carols, and wrapping gifts.

 The species of Apolemiidae may be record holders for the longest animals on earth. Fragments of specimens of this family with a length of over 30 meters have been reported from the French Mediterranean coast in the bay of Villefranche-sur-Mer. In most physonect siphonophores clones are arranged along a central stem, it itself the founding clone developed from a single egg.  At the front end, is a group of clones that are propulsion clones. Basically, Santa’s reindeer if Dasher, Dancer, Prancer, Vixen were all budded from and identical to Santa.  In the larger and remaining region of a physonect siphonophore, one can find the clones for engaging in the spirit of Christmas, eating and…  New clones are formed in special growth regions of the siphonophore.  As new clones are formed the old clones get pushed down the line. But Apolemia species are special.  In addition to other clones Apolemia can also add new feeding clones along the entire length of the stem. This fact might be the reason why members of this particular family of siphonophores can grow to such tremendous length.

The post The Ocean’s Gelantinous Christmas Tinsel first appeared on Deep Sea News.

The highest known pressure in the deep oceans coincides with the maximum known depth in the southern end of the Mariana Trench, the Challenger Deep. The actual maximum depth of Challenger Deep is disputed. The deepest reported measurement was by a Russian research vessel at 11,034 m. The International Hydrographic Organization adopted 10,924 in 1993, but a subsequent 2010 survey, and the most accurate, places the depth at 10,984 – 25 m greater. With every 10 m corresponding to 1 atmosphere of pressure, this places the maximum known pressures in the deep between 1092.4 and 1103.4 atm (110.7–111.8 MPa). Notable is that several other deep-sea trenches—Tonga, Philippines, KurilKamchatka, and Kermadec—in the Pacific Ocean also reach depths >10,000 m. In the Atlantic Ocean, the two deepest trenches are the Puerto Rico Trench at 8800 m and the South Sandwich Trench at 8428 m.

The prevalence of prokaryotic and eukaryotic life through the range of high pressures in the deep oceans suggests that organisms can easily adapt to these conditions. Even at the extreme pressures (>110 MPa) in the Challenger Deep, microbial life flourishes and differs from the background abyss. Several large multicellular organisms have been found at extreme depths and pressures and can be characterized as primarily hadal and trench species. Endemism of species occurring greater than 7000 m is 74% of surveyed species, implying a strong evolutionary pressure and the unique adaptations required to exist at extreme depths. Among invertebrates, several reach trench depths, including the sea cucumber Myriotrochus bruuni at 10,710 in the Mariana Trench, the extremely abundant amphipod Hirondellea gigas at 10,897 m in the Challenger Deep, the isopod Macrostylis species at 10,710 in the Mariana Trench, the polychaete genus Macellicephaloides at 10,700 m depth, and the sea anemone family Galatheanthemidae at 10,700 m depth. The deepest known vertebrate is the hadal snailfish Pseudoliparis swirei found at 7966 m.

How do organisms survive this deep?

1. Cell membranes: As you may remember from high school or college biology, a cellular membrane consists of lipid bilayer. The structure is entirely maintained by the interaction of charges (or lack of) between water and the phospholipids. This makes the membrane semipermeable much like a layer of oil on water. Extreme pressure results in a tighter packing of the phospholipids which lowers the permeability of the membrane. One adaptation by deep-sea animals is to increase cellular permeability is to increase the percentage of unsaturated fatty acids. In a saturated fatty acid all the carbons in the chain are lined by a single covalent bond. As you recall, a carbon can take four chemical bonds. If all these bonds are covalent (single) then a carbon could potentially attach to 4 other atoms. Thus the saturated comes from the fact that the carbon chain is loaded with hydrogens. If a carbon forms a double bond with another atom then the carbon would have to bond with one less hydrogen. Thus an unsaturated fatty acid is one with double bonds and not ‘saturated’ with hydrogens. The double covalent bond between adjacent carbons in an unsaturated fatty acid leads to a ‘kink’ in the tails of the molecule. Thus increasing their concentration in membrane leads to a looser packing.
2. Enzyme shape: At the basic level, pressures would also select for different enzymes. Changes in protein structure can influence their cellular function. Thus selection for rigidity is needed to counteract pressure and the resulting warping of proteins. Proteins contain hydrogen and disulfide bonds between different subunits and parts of the amino acid chain that both dictate structure. A selection for proteins with increased bonding would minimize changes in shape to do pressure.
3. Urea: As note by Al Dove previously, “Pressure can even make molecules more (or less) toxic.  Urea is a good example: it becomes far more toxic as pressure increases.  So deep sea sharks, which like all sharks have a lot of urea in their blood, also have a lot more of the protective chemical TMAO to offset this effect than do their shallow water cousins.”
4. Air filled sacs: Basically this is bad for an animal under pressure, so most deep-sea animals avoid having them. Deep-sea fish lack swim bladders. Other deep diving animals like whales and seals have collapsible lungs to deal with extreme pressure (not to mention a whole host of other adaptations)! Penguins basically shut down all their organs except for their heart and their brain when doing deep dives.

The post The Hidden World of Extreme Ocean Depths: Life and Pressures in the Trenches first appeared on Deep Sea News.

One species of anglerfish was filmed off the coast of Monterey, California, revealed drifting and tumbling along, humming Taylor Swift songs.  One of these may not be true.

While it was conventionally thought that anglerfish females swim upright with their lure positioned ahead, a case of inverted swimming emerged about two decades ago—a surprising deviation from the expected norm. Cue original Top Gun reference here. 

Recent research, adding eight new observations to the pool, proposes that this inverted swimming might actually be the norm for these fish. In these instances, the anglerfish maintained a rigidly straight body, with their unpaired fins erect and the lure held downwards when inverted. The tendency of these fish to swim closer to the seabed suggests a potential focus on bottom-dwelling prey. This inverted orientation likely aids in swiftly luring prey away and clearing the path for a well-aimed strike—a tactical advantage in their hunting strategy within the depths.

Stewart, Andrew L., et al. “Upside‐down swimming: in‐situ observations of inverted orientation in Gigantactis, with a new depth record for the Ceratioidei.” Journal of Fish Biology (2023).

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