Are you afraid of the deep, dark ocean? If so, you’re not alone. Thalassophobia (fear of deep water) seems all too common these days from web articles titled “10 Bioluminescent Organisms That Better Cut That Freaky Sh*t Out Before I Call The Cops,” to sci-fi thrillers like “The Meg” (2018) to Tumblr posts like that of user jaclcfrost: “make no mistake i love the ocean with my whole heart but deep water terrifies me so much.. what’s goin on down there? nothing i want to be a part of.” Indeed, the deep ocean – aquatic, cold, dark – is about as opposite an environment from our own as we could imagine. As laid out in the 2018 book Beasts of the Deep: Sea Creatures and Popular Culture: “The deep sea offers us an oppressive and foreboding context – a space unexplored, unknowable, and overwhelming.” But what is the cost of viewing over 70% of our planet with aversion – and who benefits from it?

For centuries, humans have imagined all manner of monsters inhabiting the ocean’s depths. Yet, despite decades of research, little has changed about how we talk, or think, about the deep sea. When I was young, I was fascinated by the “alien” life that inhabited the deep. “We know more about the surface of moon…” Sir David Attenborough assured me in BBC’s Blue Planet (2001), than we know about the deep sea. It wasn’t until I was offered a place on a research expedition in 2017, however, that I would see this world for myself. One morning in September, in the middle of the Pacific Ocean, I squeezed into the Pisces V submersible – a metal sphere no bigger than a small sedan. The water changed from blue to black as we descended to 1000 meters (~3280 ft). We were entering into a fabulously unknown world… Or, so I thought.

Mr. Terry Kerby, our submersible pilot, greeted each animal like an old friend (This was the Pisces V’s 889^th dive, after all). Barracks, rattails, Chaunax, Callogorgia, Corallium, Desmophyllym, Chimeras, Dories, Ophiuroids… I was taken aback by how normal these animals looked. The fish were not the deformed oddities I had come to expect. The crabs just looked like crabs. The corals, like corals. Wasn’t this supposed to be an alien frontier?

I learned an important lesson on that expedition: What most people believe about the deep ocean is, at least partly, a lie. There are many reasons why deep-sea imagery might be misleading. For one, can be difficult to get a sense of scale. Ambiguity, paired with fear and imagination, is what makes animals like the Viperfish (Chauliodus spp.) look like something that could eat you for dinner, rather than its actual length of ~30 cm (~12 in). In 2012, an exhibitionput on by the Australian Museum displayed an “oversized model anglerfish” which has since circulated around the web, passing as a real specimen (Most midwater anglerfish (Melanocetidae) are rarely more than a foot long!). The infamous mugshot of the “blobfish” (Psychrolutes marcidus), aka the “World’s Ugliest Animal,” shows the violent result of a trip to the surface. As researchers Alan Jamieson and colleagues write, “…take a domestic cat, scour its hair off, drown it in near-freezing water, pressurize it to 300 atmospheres, photograph its face, and then declare it ugly. The cat scenario would certainly be met with immediate disgust and outrage but it is exactly what the image of the blobfish portray.” Others wish to incite fear, shock, or disgust. If you search the phrase “Deep Sea Creatures,” pages of image results are inevitably returned of twisted, grotesque, and bizarre creatures – some real, many fictional. All of this works to reinforce thalassophobia.

So, people fear the deep ocean. So what? Why should we care?

The real issue with fearing the deep sea is that it is actively under threat, and there is little public outcry in response. The more people hate the deep ocean, the less pressure there is to protect it. Fear has always been a powerful political tool. From colonization to resource extraction, exploitation of an area has always been easiest when people believe either (1) nothing lives there, or (2) what lives there has no value. When the former can no longer be claimed, tactics usually shift to the latter. In the case of the deep ocean, decades of research and exploration have long since shattered the illusion of an empty abyss. Thus, we shift to the latter. People protect what they love. What does that mean for what they hate?

The deep ocean is part of our planet, subject to all its challenges and human impacts. Currently, over 3,400 deepwater drills extract oil and natural gas from the Gulf of Mexico, alone. As was vividly illustrated by the Deepwater Horizon oil spill in 2010, which spewed an estimated 3.19 million barrels of oil into the Gulf, this is not without risk. To combat this need for oil, people are shifting to electric vehicles, but this has consequences for the deep ocean, too. Many areas of the seafloor are rich in rare earth elements needed for batteries like Nickel, Cobalt, and Lithium. Thus, deep-sea mining is being explored as a means of satiating this demand, threatening to “clear cut” an area roughly the size of the continental U.S in the Pacific Ocean. Deepwater fishing not only removes targeted species from the deep sea, but also more than 38 million tons of unmanaged, unintentional, or unused species (“bycatch”) each year. Even fishing gear alone can be destructive. Around 48 million tons of “ghost gear,” or fishing gear lost at sea, are unintentionally generated each year – about the weight of 240,000 blue whales. Ghost gear may entangle and kill sea life for decades and, as most gear is made of highly durable nylon, is one of the largest sources of plastic pollution in the ocean. If deep-sea ecosystems manage to evade all these threats, however, there are still rising CO₂ levels and seawater temperatures to contend with.

If we want to protect the deep ocean, then we must actively change the way we talk about it. The deep ocean is a tapestry of beautiful environments that should be viewed with awe, interest, and fascination. For scientists, we must change how we present this place, shifting the focus away from its “alienness” to its complexity, uniqueness, and vital importance. For the public, we must make an active effort to learn about the reality of the deep ocean and combat misinformation. With resources available like NOAA’s Deep Ocean Education Project and livestreams of deep-sea dives, there’s never been a better time to learn about our deep oceans. Fear is never neutral. Being conscious of how emotions like fear and disgust can be used against us is a crucial step towards ocean stewardship. The deep sea is a frontier, but it is much less scary, and way more interesting, than you might think.

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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.

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In 1964, the Antarctic oceanographic research ship USNS Eltanin made the above photograph of the sea bottom west of Cape Horn. The Poles: the final frontier. These were the voyages of the USNS Eltanin. Its 10-year mission: to explore strange new polar worlds. To seek out new life and survey new sealfoors. To boldly go where no man has gone before! Between July 5, 1962, and December 29, 1972, Eltanin conducted 52 Antarctic research voyages, covering approximately 80% of the Southern Ocean and traversing a cumulative distance of 400,000 miles. During these missions, Eltanin gathered magnetic profiles of the seabed, which played a crucial role in substantiating the theory of continental drift by confirming the phenomenon of sea floor spreading.

But back to the aliens. When the above image was published, due to its regular antenna-like structure and upright position led many to postulate was of extraterrestrial origins…an alien antenna

The initial public reveal of this intriguing image occurred when it grabbed attention in the New Zealand Herald on December 5, 1964, under the headline “Puzzle Picture From Sea Bed.” However, the enigma only deepened as additional layers unfolded. In 1968, Brad Steiger contributed to the intrigue with an article in Saga Magazine, suggesting that the Eltanin had captured something truly baffling—a curious apparatus resembling a fusion of a TV antenna and a telemetry antenna at with the height of 1.6 meters. Note there is no idea of scale in the original image so the height was pure conjecture. Various theories continue to circulate during that period, ranging from suggestions that it was a mere fragment that had accidentally dislodged from a vessel to more speculative notions, including the belief that it might be a clandestine endeavor of the Russians, or even more far-fetched hypotheses involving extraterrestrial involvement.

The biologist Dr. Thomas Hopkins, would say of “I wouldn’t like to say the thing is man-made because this brings up the problem of how one would get it there … But it’s fairly symmetrical and the offshoots are all 90 degrees apart”

But apparently all these UFO enthusiasts had missed the 1971 book The Face of the Deep by Bruce C. Heezen and Charles D. Hollister. Hollister who had already identified the mysterious object as Cladorhiza concrescens, a carnivorous sponge. As pointed out by Heezen and Hollister, in 1888, Alexander Agassiz drew the odd creature in Three Cruises of the Blake. From 1877 to 1880, the U.S. Coast and Geodetic Survey dispatched the steamer Blake on three cruises of discovery—two expeditions to Florida, the Gulf of Mexico, and the Caribbean and one off the eastern Atlantic coast as far north as the Gulf of Maine. These cruises were designed to increase knowledge of the depths of the oceans and the animals and plants living on or near the bottom and to pioneer technological advances in oceanography You can access the entire Agassiz’s Three Cruises of the United States Coast and Geodetic Survey steamer “Blake”, in the Gulf of Mexico, in the Caribbean Sea, and along the Atlantic coast of the United States, from 1877 to 1880 online. Agassiz described the strange sponge as having a long stem with ramifying roots deeply embedded in the mud, adorned with nodes bearing four to six club-like appendages, covering extensive portions of the seabed like bushes.

Below is screen grab from remote operated vehicles from the Monterey Bay Aquarium Research Institute from one of my dives of Cladorhiza concrescens on the seafloor. Indeed the Cladorhizid carnivorous sponges often have these very spectacular forms with 90 degree angles and intricate structures. I always refer to C. conscescens as the lollipop tree sponge.

However, this identification by Heezen and Hollister remained large ignored. In 2003, a discussion on email list prompted marine biologist Tom DeMary to reach out to A. F. Amos, an oceanographer who had been aboard the USNS Eltanin in the 1960s. Amos had know of the identification of the antenna as sponge and direct DeMary to the book by Heezen and Hollister. DeMary then shared this more broadly.

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The post Friday Video: Top 10 deep-sea animals from MBARI 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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Connecting the oceans to land are numerous carbon highways.  These conduits bring food from land to the ocean, supporting an abundance of life.  Our group explores these carbon chains and explores some potential methods of carbon delivery to the deep.  Thus, alligators on the abyss.

At first it may seem fanciful that an alligator carcass might find its way to the deep.  However, dozens of species of alligators and crocodiles are found across the globe, in high numbers, and often in coastal areas.  Through either their normal migrating or foraging activities, or during flooding events, individuals may be found offshore in the ocean.  If one of those individuals meets an unfortunate end, it may fall to the seafloor.

In prehistoric times, the impact to the deep oceans could have been even larger, as large reptiles such as ichthyosaurs and plesiosaurs dominated the sea. Deploying a reptile in the deep sea today may reveal the animals that specialized on the carcasses of long-extinct ancient emperors of the sea.

Earlier this year, our research group placed three alligator carcasses 1.5 miles deep on the seafloor of the Gulf of Mexico in the first-ever alligator fall experiment.  Each of the three alligators met a different fate.

The first alligator had been on the bottom of the ocean for less than 24 hours. Despite the tough hide of the alligator, scavengers quickly got through and began to gorge themselves on the flesh of the alligator. Football-sized animals called giant isopods, relatives of rolly pollys or pillbugs, penetrated the hide in this short time-frame.  This demonstrates the speed and precision with which deep-sea scavengers can utilize any carbon source, even food from land and freshwater systems.

A little over 60 miles to the east of the first alligator, the second alligator had been sitting on the seafloor for a little over a month and a half.  All the soft tissue of the alligator had been removed by scavengers.  A small animal called an amphipod was still darting around looking for scraps, but the only thing that remained was a skeleton.  All of the soft tissue had been consumed. The spine curved just as it had been left.  A depression in the sediments indicated where the full body once laid.  The skull was turned over, likely by scavengers while picking at the flesh on the skull.

A fuzzy carpet covering the bones of the second alligator represented a brand-new species, previously unknown to science.  These zombie worms, or Osedax, colonize the bones of many types of vertebrates and consume the lipids within.  This was the first time zombie worms had ever been observed in the Gulf of Mexico or from an alligator fall.  They also demonstrate yet another pathway in which carbon from land makes its way into deep-sea food webs.

Another 60 miles east lay the third alligator.  It had only been eight days since it was laid on the seafloor.  As the camera panned to the marking device, a floating bucket lid attached to a rope like an underwater flag, it became clear that the alligator was missing.  All that remained where it had been dropped was an alligator-shaped depression in the sediments.  Drag marks in the sediment paved a path to what remained of the alligator fall.  An animal dragged this alligator 30 feet and left only the 45-pound weight and rope.  The rope had been bitten completely through. To consume an alligator, and create this disturbance, the animal must have been of great size.  We hypothesize that most likely a large shark, like a Greenland shark or sixgill shark, consumed this alligator whole.

Three alligator falls in the abyss met three very different ends, from being consumed by football-sized cousins of rolly polys, to zombie worms eating their bones, to a large shark dragging it away and consuming it whole.  This research has given us a glimpse into what impact large reptiles had in past oceans, as well as the role they play today.  It is clear that deep-ocean scavengers have no qualms about successfully and quickly consuming food that originated on land or freshwater.

Read more about this research in our group’s recent publication in PLOS One: “Alligators in the abyss: The first experimental reptilian food fall in the deep ocean.”

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A four-leaf clover represents just one kind of rareness. One might find a 4-leaf clover just about anywhere. Four-leaf clovers are not just restricted to Ireland. Four-leaf clovers are rare because at any given locality they occur in very minuscule numbers.

The idea of whether rareness imparts values has tormented philosophers, including Nietzsche. “Whatever can be common always has little value. In the end it must be as it is and always has been: great things remain for the great, abysses for the profound, nuances and shudders for the refined, and, in brief, all that is rare for the rare.” But of course, Nietzsche does not define rare. What does “all that is rare for the rare even mean?” Freakin’ Nietzsche.

We all feel we know what rare means. But contrast the case of four-leaf clovers with platinum. Platinum is special for me. For my 10th wedding anniversary, I had a custom wedding ring made of platinum for my wife. This platinum band was to replace one from our youth when I had more limited income and could afford a metal less “precious” and less “rare.” Yet, platinum represents another kind rarity, occurring in great abundance but only at a few locations. Locally abundant but geographically restricted.

In a classic 1981 paper, Dr. Deborah Rabinowitz, a professor at the University of Michigan, laid out the seven forms of rarity. What makes something rare depends on three characteristics; geographic range, habitat specificity, and local population size. First, is a species found globally or only at a single location? Two, is species seen at any given site in low numbers? Third, is the species only found in a specific type of habitat?

As Rabinowitz notes in elegant writing., “If each of these attributes is dichotomized, a 2 x 2 x 2 or eight-celled block emerges. Although creating the hazard of false reification – that is, converting an idea into an object – such a simple scheme can aid in focusing our thoughts, and this is my intention. The patina – a gloss or incrustation conferred by age – of monolithic rarity may have hindered our understanding of an exceedingly heterogeneous assemblage of organisms. Since the products of rarity are diverse, the causes of rarity and the genetic and population consequences of rarity are undoubtedly equally multiple.”

But obviously, 2x2x2 does not equal 7. One state is lost, a species found everywhere, in high numbers, and several different kinds of habitats. This species isn’t rare at all! You can think of the seven forms of rarity as three singe type cases (geographically limited/small numbers/habitat specialist), the three double type cases (geographically limited and small numbers/geographically limited and habitat specialist/small numbers and habitat specialist), and the last triple case (geographically limited and small numbers and habitat specialist).

The most uncommon form of rarity is a species found all over but in limited numbers at a single location. One such species is the exceptionally beautiful deep-sea snail Oocorys sulcata found in the eastern and western corridors fo the Atlantic and reaching will into the Indian Ocean and the western Pacific. Oocorys sulcata also show incredible depth tolerance found all the way from the shelf at 150 meters down to the deepest abyss over 5000 meters. Yet, despite this fantastic distribution, it is rarely found. A famous sampling effort off of New England did not capture a single individual in 41 samples. Another 24 samples later as part of later effort only yielded a single specimen. Indeed, based on some very rough calculations, you would probably only find about 15 every square kilometer or roughly 45 Manhattan city blocks.

Hydrothermal vents possess mollusks that are both unique and fascinating. A snail first described in 2003, the unusual snail Chrysomallon squamiferum, maybe the most exciting find thus far at a hydrothermal vent. I admit my bias here, as most of my interest lies with studying deep-sea snails. Nonetheless, the discovery of “gold-footed” snails a the Kairei vent field in the Indian Ocean is fascinating.

At this point, I should state that the foot of the snail is mineralized with pyrite and greigite. Many of you might note the misnomer here, as pyrite is only ‘Fool’s Gold,’ but in deciding on a temporary ordinary name Fool’s Gold-Footed Snail seemed a bit lengthy. I hope all will forgive the intentional misnomer for the sake of creative writing. Although other names due include the big-hearted iron snail (it also possesses an abnormally large heart for its size). And of course the scaly foot snail. So maybe the big-hearted, iron gold, scaly foot snail.

The scales, or sclerites, that cover the entire length of the snail’s foot can be up to 8mm long. The presence of mineralized scales is remarkable in itself, but the existence of iron sulfide as skeletal material is unknown from any other animal. The purity of sulfides, among other lines of evidence, suggest that the building of the scales is controlled by the gastropod itself. The sclerites are thought to have evolved recently and homologous to the operculum. It is believed they may serve as a defense against cone shells also occurring at the vent.

Chrysomallon squamiferum is rare, not only for the oddity of its features amongst the animal kingdom but because the snail is known from only three hydrothermal vents in the Indian Ocean. While abundant at any of these vents it is geographically restricted, like platinum. The scaly foot is actually a “double rare” case both geographically restricted and a habitat specialist. Given this potential habitat of only a few square meters, some of which endangered by deep mining interests, led a new paper by Dr. Sigwart and colleagues establishing Chrysomallon squamiferum as endangered on the IUCN RedList. This listing places the big-hearted, iron gold, scaly foot snail with 25 species all either bony fish, cartilaginous fish, or cephalopods all assessed to be either endangered or critically endangered.

Helen Macdonald writes in H is for Hawk “The rarer they get, the fewer meanings animals can have. Eventually rarity is all they are made of. The condor is an icon of extinction. There’s little else to it now but being the last of its kind. And in this lies the diminution of the world. How can you love something, how can you fight to protect it, if all it means is loss?”

I am hoping for future where Chrysomallon squamiferum I remember this elegant mollusk for the rarity of beauty, adaptation, and morphological marvel not the rarity of its existence.

Sigwart, J. D., Chen, C., Thomas, E. A., Allcock, A. L., Böhm, M., & Seddon, M. (2019). Red Listing can protect deep-sea biodiversity. Nature Ecology & Evolution, 1.

Rex, M.A., Stuart, C.T., Etter, R.J., & McClain, C.R. (2010). Biogeography of the deep-sea gastropod Oocorys sulcata Fischer 1884. Journal of Conchology, 40, 287.

Rabinowitz, Deborah. (1986). Seven forms of rarity and their frequency in the flora of the British Isles. Conservation Biology: The Science of Scarcity and Diversity 

Rabinowitz, Deborah. (1981) Seven forms of rarity. Biological Aspects of Rare Plant Conservation

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These bada$$ carbons are “isotopes”, sort of like fraternal twins (or triplets/quadruplets) where one is blazing their own path.  One of the twins is your regular Joe Shmoe who follows the rules and does everything by the book.  These are the ones shown in the periodic table.  The other twin in each set has the same number of protons as its boring twin, but it doesn’t follow the rules about how many neutrons they are supposed to have. They’re greedy little thieves. So, they are technically the same element, but they end up weighing different.  For instance, Carbon-13 has his regular six protons like its brother, but it has a whopping seven neutrons because it just haaaad to go and be extra cool. 

Almost every element has some number of isotopes/twins, except weird ones like Thulium and Holmium – but who even are those guys? Now, the wrong-number-of-neutrons outlaw twin can either be “stable” or “unstable”.  It’s like the difference between the cool guy in class and the guy who is so “cool” that he ends up expelled from school.  The stable ones are functional in society – in this case meaning they occur in nature without a problem.  The unstable ones are completely dysfunctional and over time try to turn back into their more stable twins by shedding neutrons.  It’s kind of like they just went too neutron-crazy, got a little wild, and now they’re all bloated and not having a good time. 

Knowing about these different carbons is important because stable isotopes can help reveal food webs.  Naturally occurring carbon consists of both the normal carbon and its bad boy twin.  We have a method that allows us to measure the ratio between the outlaw and the normal (we call this ratio the isotopic ratio). By measuring the carbon isotopic ratio of an animal, we can answer questions like what did this animal eat, what level consumer are they, and even what kind of eater are they (suspension feeder, predator, etc). This is especially important in my work because I want to understand how carbon from land makes it into the deep-sea food web. When I drop a big hunk of land carbon in the form of an alligator or a wood log (wood fall), I first measure the ratio of good boy to bad boy carbon in that particular hunk of food.  I also collect samples of the sediments around where I drop the food and measure the ratio of carbons in that sample too.  Then, after letting the food stay on the bottom of the ocean for a while, I can take animals directly off of it and take similar animals far away from the it.  When I measure the ratio of carbons in these animals, I can compare them to the ratio of the two food sources I measured and can understand which food source the animals are using.

The reason this all works is because of the saying “you are what you eat.”  Turns out that is actually true!  We know how much the good boy to bad boy carbon ratio should change from a food item to its consumer. This is especially helpful as we begin moving up the food web, because we can start to see who is eating whom – and this is something not yet well understood in the deep sea.

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After Pliny’s monstrosity, many centuries went by before this question was really tackled again.  In 1815, Edward Forbes took a ride aboard the HMS Beacon, where he dredged the bottom at depths from 1-1,380 feet (0 – 420 m).  Just so you know, the average depth of the ocean is about 12,000 feet (4,000 m).  So, when I say he was barely scratching the surface, I’m not really exaggerating.  But nevertheless, he dredged the depths that he did and found that the deeper he dredged at, the less things he found.  So naturally, he thought, there must be a “zero point” at which no animals live.  He wildly extrapolated his data and determined that below 1,800 feet (600 m) there exist no animals, and he called this the “azoic zone.” So, Forbes’ answer to how many species in the deep sea was a big fat “not many.”

Luckily this “azoic zone” nonsense only lasted about 50 years.  In 1869, Charles Wyville Thomson and the rest of the crew onboard the HMS Porcupine pulled up animals from 14,610 feet (4,450 m) deep in the waters south of Ireland.  These results were later confirmed by the Challenger expedition which found animals at all depths, all over the globe.  This undeniably proved there was life at all depth of the oceans- but the question still remained.  How many species in the deep sea?

Fast forward to 1992.  Frederick Grassle and Nancy Maciolek conduct a massive (for the time) survey of the tiny animals that live in the sediments in the deep sea.  These are not the cute crawlies that live on top of the mud that had been previously sampled with dredges.  These are the small animals that live their lives between the grains of dirt at the bottom of the ocean.  Of the 798 species that they found, over half were new to science!  Pliny’s head would explode if he heard that more than double the total animals he thought existed in the whole ocean were found just in the mud.

Grassle and Maciolek did some impressive math and ended up calculating that they were finding one new species per square kilometer they sampled.  Let’s break that down.  One square kilometer is equal to a little more than one-third of a square mile.  So, they are basically finding three new species in each one-mile-square block of mud they are sampling.  This means if they were to sample an area the size of New York City, they would find around 782 new species, and if they were to sample an area the size of London, they would find about 1,572 new species.  These new species add up fast – you see, there are 300,000,000 square kilometers (115,830,647 square miles – almost 30 Europes or 431 Texases) of mud deeper than 1000 m in the ocean. The end result of all this is a conclusion of 300,000,000 species living in the mud at the bottom of the deep ocean.  This is not counting swimming things!  That’s a heck of a larger estimate than the 176 species estimate of centuries ago.

.It turns out that this calculation of Grassle and Maciolek was probably a bit of an overestimation.  They realized that much of the ocean is oligotrophic, or not very nutrient-rich and therefore not very productive.  This would mean that in many areas of the ocean, the rate of new species added per square kilometer is probably much less than what they found in their sampling area.   So, they ended up conservatively estimating the true number at more like 10,000,000 species in the mud. This is still a huge amount of diversity in the deep sea.

Grassle and Maciolek’s 10 million species hypothesis sparked quite the controversy, with biologists from many sub-disciplines quickly arguing for or against the high number.  Isopod biologists Poore and Wilson said they had seen even more diversity just among isopods in their samples than the average number of species per 100 samples that Grassle and Maciolek had used in their calculations.  This, they argued, must mean there are even more than 10 million species!  In 1971, though, Thorson argued that there were only 160,000 species in the oceans across all depths- so far less than 10 million could be in the deep sea.  In 1992, May argued that only 500,000 species would be possible in the deep sea.  Lambshead in 1993 reminded everyone that there are a boatload of nematode worms and other animals (collectively called meiofauna) that live in the mud that were too small to be sampled by the gear Grassle and Maciolek used.  This, Lambshead argued, could mean a total of 100,000,000 marine species.  Consensus just could not be reached.

Here’s the problem, though.  It is a hard question to answer.  Each person who has attempted to answer this question was doing the best with the data that they had at the time (except Pliny- that guy was just an idiot okay). However, species diversity and especially how many species you discover in each new deep-sea “block” can vary considerably at different depths, regions, and oceans. Grassle and Maciolek’s encoutering 3 new species per block was based on data from the North Atlantic. Does 3 new species “rule” also apply to other parts of the Atlantic or to the Pacific? So without massive amounts of data, it is likely we will be kept guessing for a few more years to come. So, I can’t tell you exactly how many species are in the deep sea, but I can tell you that we currently have 409,543 named species in the ocean (World Register of Marine Species, accessed 03/18/2019).  The best part is that we are getting better and better at discovering new species, and hopefully in years to come we will be much better equipped to answer this question realistically.

Cover photo credit to Monterey Bay Aquarium Research Institute (MBARI).

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Prior to 1967, the environmental extremes of the deep were thought to limit life. The deep sea is dark (can’t-see-your-hand-in-front-of-your-face dark), cold (only-four-degrees-above-freezing cold), and under an extreme amount of pressure (one-elephant-on-each-square-inch-of-your-body pressure).  This suite of factors should make survival challenging, and thus for a century, scientists assumed the deep sea was biologically a desolate wasteland.  Even after the discoveries of animals living at extreme depths in the late 1800s, Victorian scientists expected that there could not be a diverse array of animals surviving in the deep sea.  Enter Robert Hessler and Howard Sanders who in 1967 used newly developed sampling devices to discover that the deep sea is shockingly diverse, and perhaps just as diverse as tropical shallow-water habitats. 

Scientists were completely baffled as to how high diversity could occur in such a bleak place.  They began to throw out theories, but they were limited by the little data that had been gathered from a poorly explored deep ocean.  The scientific publications of this time on deep-sea diversity read like there were a few people in a room with a whiteboard, writing everything they remember from their ecological textbooks, talking through each theory, slowly crossing off possibilities, and working their way down the list.  

Howard Sanders began by writing “Specialization” on the whiteboard with his paper introducing the Stability-Time Hypothesis in 1968.  He suggested that because the deep sea is monotonous and predictable (i.e., it is stable), populations have the evolutionary time to become newly specialized in how they feed. Over time, these populations become so specialized they evolve into totally new species, eventually driving diversity up.  Further research and explorations indicated that the premise of this argument was wrong- the deep sea is actually not that stable.

Then, Paul Dayton and Robert Hessler walked up to the board and scratched off the “Specialization” idea with their paper in 1972 entitled “The role of biological disturbance in maintaining diversity in the deep sea.”  The pair do not argue against the idea that the deep sea is predictable and stable.  In fact, they favor the idea… except for the part where they proved that deep-sea species are actually not more specialized than shallow water species.

“Specialization” got a strikethrough on the whiteboard, and Dayton and Hessler wrote “Predation” below it.   The duo introduced a specific type of predation pressure they labelled “biological cropping.”  No, biological cropping is not deep-sea animals learning agricultural techniques… but a combination of predation and deposit feeding.  Animals can eat other animals either intentionally (e.g. hunting down prey) or unintentionally (e.g. stuffing everything you come across into your mouth and it just so happens that you get a live one).  This “cropping,” whether accidental or not, reduces competition by preventing one or a few abundant species from monopolizing the resource.  These species get knocked out, allowing far more species to get a piece of the proverbial pie. Nobody gets sent into extinction by competition.  Dayton and Hessler’s idea is not necessarily that diversity is driven to be high in the deep sea, just that it is not limited.

Dayton and Hessler’s “Predation” idea never got fully scratched off the list, but the difficulty of testing the idea and conflicting results have led many to write large question marks next to it.   Many other ideas now are situated below “Predation,” including: “Disturbance,” “Patchiness,” and “Successional Dynamics.”

Ultimately, those of us in the deep-sea scientific community are still today standing around the dry erase board bouncing many of these same ideas off each other.  Sometimes we manage to cross one off the list, or add one, or at least add to our understanding of the ideas.  One thing is clear though, we still haven’t gotten it all figured out.  So… anyone have a dry erase marker?

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