As I watched the monitor as we descend a 75-foot-tall chimney. Charcoal black to grey fluid is violently erupting from the top and several cracks along the chimney’s surface. You could see the shimmering sheen in the water, indicating that the temperatures were far above those of the surrounding, freezing abyss. Hydrothermal vents are home to the highest recorded temperatures on Earth. At oceanic ridges, where rocks are often brittle and fractured, cold seawater percolates down through Earth’s crust, gets superheated by magma, and rises back to the surface. Currently, the “Two Boats” vent in the Turtle Pits field along the Mid-Atlantic Ridge holds the record for the hottest hydrothermal vent, with fluid temperatures reaching up to 867.2˚F (464°C), nearly four times greater than the boiling point of water at 212˚F (100˚C). The extreme pressure prevents this boiling from actually happening.

At some vents lives the curious little worm, Alvinella pompejana. Discovered in the early 1980s by French scientists, the Pompeii worm is about 4 inches long with tentacle-like, scarlet gills on its head. Its name hints at its high-temperature habitat, being derived from the ill-fated Roman city of Pompeii, destroyed abruptly during an eruption of Mount Vesuvius in 79 A.D. The scarlet worm is found on the sides of hydrothermal vents, with its tube often reaching across the chimney to access some of the hottest vent fluids. The worms can be briefly exposed to 212˚F (100˚C) waters, although temperatures adjacent to the worm’s tubes more often range between near freezing and 113˚F (45˚C). In fact, the rear end of the species likely experiences extreme heat while the front end experiences extreme cold, making it the most eurythermal (capable of surviving a wide range of temperatures) species on earth.

How Alvinella pompejana survives in this boiling hot environment is still somewhat of a mystery. One theory is that the worm can keep itself cooler, between 68-83°F, by pulling cold water into its tube when it moves in and out, and with the help of bacteria that circulate the water around its body. This gray layer of bacteria covering the worm’s back, besides moving water, may also provide it with a sort of thermal blanket. The worm’s skin and connective tissue also have the most heat-resistant proteins known, thanks to their special structure. Additionally, the worm’s DNA has more triple bonds from guanine-cytosine (GC) pairs compared to other similar species, which helps it stay stable at temperatures up to 190˚F (88°C).

The post A Journey to the Hottest Place on Earth: Hydrothermal Vents and the Resilient Pompeii Worm first appeared on Deep Sea News.

Jack and squat is known about free-living flatworms form the deep sea. Their fragile bodies are unlikely to be collected successfully in dredges and trawls. This means that outside of ‘potential platyhelminth’ from a wood fall and deep record of another species little else is known.

A new study adds to our limited knowledge of these beasties. Flatworm egg capsules were retrieved from rocks found approximately 6200 meters deep in a trench in the northwestern Pacific. Despite each capsule being a diminutive 3mm in size, they housed anywhere from 3 to 7 individuals. Through the application of genetic tools, the researchers identified a new species within a group previously only observed in shallow waters.

Kakui, Keiichi, and Aoi Tsuyuki. “Flatworm cocoons in the abyss: same plan under pressure.” Biology Letters 20.1 (2024): 20230506.

The post Flatworm cocoons in the abyss 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).

The post The Upside Down Feeding Fish of the Deep first appeared on Deep Sea News.

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.”

The post Alligators in the Abyss: Part 2 first appeared on Deep Sea News.

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

The post The Beauty of Rarity first appeared on Deep Sea News.

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.

The post You are what you eat! Using bad boy carbons to understand food webs first appeared on Deep Sea News.

The video is the actual video from my research group’s dive with a remotely operated vehicle in the deep Gulf of Mexico. The background on all this alligatorfall project and why a bunch of scientists would sink an alligator in the first place is in our previous post. You can also read Atlas Obscura’s great write up on our work.

The post The Video of Giant Isopods Eating an Alligator in the Deep Sea You Must Watch! first appeared on Deep Sea News.

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).

The post How many species are in the deep sea? first appeared on Deep Sea News.

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?

The post How is the deep sea so diverse? The struggle is real for late 1900s ecologists first appeared on Deep Sea News.