Hunters of the Dark Ocean, Part 4

in order. But for a brief recap of previous episodes, we talked about how the ocean can be thought of as having different environments or zones stacked vertically on one another, which,

according to their depth, have different conditions. Closer to the surface, of course, there's more warmth, less pressure, more access to sunlight for phytoplankton to feast on, and thus more access to food all the way up the chain, and then as you go deeper, the waters get colder, darker, pressure, goes up, food resources become more scarce or at least

less dense. And what this means is that much like how terrestrial animals are evolved to live in one type of environment and not another, marine organisms are usually adapted not just to the ocean or seawater, but to a specific zone of the ocean. So kind of like how you're not going to find jaguars living in the middle of the Sahara. You don't find the frosted flatwood salamander in the Midwest prairie. You also don't find tuna living

in deep ocean trenches like eight thousand meters down. And there are some adventurous boundary crossers, but most ocean fauna are adapted to a fairly specific depth range, and the majority of those animals do live near the surface, where

conditions are less extreme and resources are more plentiful. But in this series, we are interested in the creatures that can be found farther down in the darker parts of the ocean, from the sort of twilight and midnight midwaters, all the way down to the abyssal planes on the ocean floor and even further down into deep sea trenches. Specifically, we have been looking at predators in these environments now.

In Part one, we talked about a recently discovered species of ghostly predatory crustacean from almost eight thousand meters down

in the Atacama Trench of the Southeastern Pacific. This new species and genus was announced in a paper in November twenty twenty four, and that example sent us off examining the positively wacky body forms of crustaceans called amphipods the order to which this animal belongs, especially their deep sea varieties, some of which had major toxic jungle charisma, others were a little more like dead Dreamer in the Nightmare City, the shapes seep down from the stars, that sort of thing.

We also talked about giant predatory siphonophores, extremely weird and amazing organisms that really defy our common understanding of what it means for a creature to have or be a body, and we discussed probable sightings of an unidentified predatory cephonophor

in a deep ocean trench environment. In Part two, we looked at a somewhat obscure abysslefish known as the grid eye fish, which was notable to me because of its bizarre neon yellow bean shaped eye cups, and then after that we talked about a couple of cephalopods, the strawberry squid with its interesting midwater camouflage methods and a kind of bifurcated method of sight, one eye specializing in seeing shadows from above and other eye specializing in biological self

illumination from below. And we also talked about oh grimpo tooth is the mbo octopus, durable little octopod who seems to have forsaken many of the biological self defense options evolved by its cephalopod kin in exchange for adapting to deeper waters where it has less pressure from its own predators.

And in part three we talked about snail fishes. These are a big player, big deal in the deep ocean family of fishes that can be found in the form of many deep adapted species, including the deepest swimming fish ever convincingly documented by science, at least as of now. The deep dwelling varieties of snailfish often look like fat, slimy, pale,

pink tadpoles with translucent skin. In the words of one article, we talked about guts wrapped in cellophane in my observation, kind often like a wad of sea through chewing gum with a tail, but when the angles were just right. Of course, as you pointed out, rob they can also be surprisingly cute, with kind of plaid said unassuming eye spots making them look like a creature of the hundred acre wood. Yes, yes, but one whose skin is dissolving.

But despite looking either like a half dissolved a meal from RoboCop or like a cute little piglet fish, it turns out snail fishes are the top predators of many deep ocean trench environments, so they eat amphipod, scavengers and other little animal forms you find down there. They're kind of the kings and queens of the underworld. Oh and also there is good reason for suspecting there's some of the worst smelling fish on Earth. We discussed in that episode why that is likely the case.

and the doom cute prey lure. There are also really interesting questions about their relationship with the bacteria they farm to create their glowing lure, how do they acquire these bacteria, et cetera. And also we talked about their truly amazing mating and reproduction practices, with the tiny male grafting its body onto that of the much larger female to become a kind of carry along sperm dispenser, which itself requires

interesting adaptations. For example, in the anglerfish immune system, how does the anglerfish avoid rejecting the grafted male's tissue and could knowledge of this sort be used to improve outcomes for organ transplants and other related issues in human medicine. Anyway, that's all the previous episodes. Today we're back to round out the discussion of dark ocean predators with our fourth and final part.

set in on their meal. So, in other words, they're two large meals rotted in their giant gut before their stomach could break it down, resulting in all those decomposition gases turning the fish into a surface bound rock balloon, which just takes them out of their deep water habitat right up to the surface, killing them.

it's not that there's no diversity. There is diversity in shallower waters, but you'll find a lot more fish there, all doing the same thing with their bodies.

and functional diversification. We explore this idea through an analysis of body shape evolution across ocean depth zones in over three thousand species of marine teleost fishes. So what did the survey yield? Well, yes, the authors found that quote morphological disparity of marine fish body plants incrementally increases nearly

two fold from ocean surface layers to the deep sea. Now, how do you measure morphological disparity that variable they're looking at there, Well, they looked at all these different species of fish, thousands of different species from different parts of the ocean, and they compared a bunch of different measures, so basic body dimensions, length, depth and width, jaw size, head size, size of what's called the caudal peduncle basically the fleshy, tapering heart of the fish leading to the

tail fin kind of the bridge to the tail. And they used these measurements to create a sort of graph or morpho space for the fish found in each zone. And what they found was that in shallower waters, while there is plenty of diversity, the body forms of different fish species tend on average to be more clustered around a standard kind of optimized design. There's just a lot more sameness.

shallow water fish. There's gonna be just a a ton of fish that are shaped basically like this.

And interestingly, quote, it is at these intermediate depths that a body plan almost nonexistent in shallow waters begins to appear, and that is quote species with elongated and tapered tails. So it's interesting we've mentioned a couple of abyssle and hatelfish fish in the deepest deepest parts of the ocean, the Abyssle plains and then even deeper than the Hatele zone in the trenches, and both of these fish species tended to have something like this design they're mentioning here,

elongated bodies with tapering tails. Kind of interesting. Finally, in the deepest part of the sea, the authors found the greatest diversity of body forms mapped on the morphospace, especially landing in extremes along the axis of body elongation.

deep deep water. But you also get this other extreme, the fish that are so long and thin they're like a string almost, and yet they are still fish.

fishes with huge mouths relative to their bodies. Big mouths and strangely tapered tails like we saw with the snail fish, so it looks like a tadpole, you know, instead of spreading out like most fishtails you think of, it just kind of tapers off to a little pencil tail. So there is a huge difference here, essentially double the evolution of disparate fish body forms in the deep zone compared to the near surface zone, where you just see a

lot more species with similar body forms. What explains this well, The authors have some ideas, and those ideas come back to something we've touched on already in earlier parts of this series, the interaction between light conditions and predation. So in the photic zone of the ocean, where sunlight penetrates the water, the authors talk about how there is a lot of hunting by sight. Predators can see prey and vice versa. Pray can see predators at a relatively long distance.

So there is predator and prey, you know, awareness of each other with significant distance in between. And it seems like when predators and prey can see each other at a distance, it gives rise to these kind of recurring predation patterns, things like stalking and chasing. Survival often becomes a literal race, where like swimming speed and maneuverability are the key factors that determine whether you live or die. So there's an arms race based around swimming speed. And

I don't know if this is a good analogy. The authors don't make it themselves, but it also made me think about how it seems to me that there is a lot of evolutionary pressure for like quadrupedal mammals to specialized for speed when they live in very open environment, something of like the savannah right right where you sightlines

are long. So the snapper form that we talked about that is so common in shallower waters maybe just kind of an optimized evolutionary design for the light drenched environment that leads to this arms race on swimming and the authors so that's one part of it, the main predation

interactions predator prey interactions based on light. Also, though they point out that shallow water fish face physical environmental pressures that deep water fish usually do not face, and there are actually a lot of different things to consider here. So near the surface, you're going to have like surface weather effects and turbulent waters and more variable current that you might need to fight against, fighting against unpredictably flowing water.

And also if fish live in coastal environments or along rocky seafloors, they might be needing to have ways of dealing with those environments, like rocky bottoms or reefs, maybe ways of hiding and getting around in those places. Those just create all different kinds of new evolutionary pressures. The conditions in the deep ocean, on the other hand, are relatively stable. You're not going to be fighting with a lot of weather or current or you know, like there's

not a lot of different stuff going on. There's going to be a lot of floating or sitting and scuttling around along the kind of sedimented bottom.

happens quickly in close quarters. And that's kind of interesting because it seems that this change in light conditions and the relatively short information horizon on which you can detect the presence of a predator or prey animal, it kind of relieves the otherwise overwhelming evolutionary pressure on swimming power like speed and maneuverability, and it allows deep adapted species to run weird experiments in survival, for example, by favoring

body types that swim relatively slowly but can serve metabolic energy or specialize in surviving in extremely high pressure and low temperature environments. And the authors point out that this explanation is supported by the observation that many deep dwelling species of fish have kind of weak muscles. They have like low density or what are called watery muscles, which does probably make them weaker or slower swimmers, but it

also helps in other ways. It helps them maintain neutral buoyancy, so that's the ability to neither float up nor sink, just kind of sit right where you are in the water column. They also point out that the extreme hydrostatic pressure of the deep ocean may actually make efficient swimming easier. Quote in laboratory settings. European eels experienced approximately sixty percent

lower cost of transport under high pressure conditions. Elevated rates of evolution for locomotor traits in the deep ocean may therefore reflect the relaxation of strong selection for some aspects of locomotive performance, such as maneuverability and high speed cruising. So I thought this was interesting because it seems like, ironically, these extreme conditions in the deep ocean allow for more biological diversity and less grouping around these body shapes that

get used over and over. It's sort of the opposite of what you would think. You would kind of think that the extreme environments would tend to force a lot of like a much narrower range of what could survive there, and instead it proves to be a kind of experiment kind of free experimentation space for evolution. And so that's interesting. Maybe I want to come back to that in a minute.

But there are also it's worth pointing out there are a few things about the deep ocean that might be thought of as analogous to the pressure on swimming speed and maneuverability in the shallow ocean. One thing is the overwhelming pressure to not miss out on a chance to eat, and that leads to one thing that they found, a thing that's not variable. Among deep sea fishes, they almost all seem to have big mouths, specifically long jaws. This

goes back to your black swallower example. In that example, it was the stomach, though I suspect it probably also has relatively large jaws compared to fish of its size throughout the ocean. But the thinking here is that the big mouths, the long jaws is about resource scarcity, kind of like the big stomachs the author's right quote befitting

rare encounters with sparsely distributed prey. So it's like when you come across food, you just do not want to miss the chance because you're already full, or because you can't fit the prey in your mouth, or because maybe you bite it but you don't have a good grip and it gets away. You just want to make sure that when you come in contact with the scarce spit of food, you are keeping it and you can digest it.

energy when you're kind of elongated like that. And also I did come across one study proposing that elongated or tapering body forms make it easier to swim backwards, which I thought was of interesting, saying that if you have an elongated body form like some of these fish, it's easier to suddenly reverse direction and go back in exactly.

to specialize for speed and maneuverability. So that is one thing that's kind of specific to the ocean, but in the more general sense, it makes me wonder if we have a tendency to think about plentiful, abundant, easy living environ min's the wrong way, you know, Like when an environment has a lot of food and opportunity and it's easier to live in, it makes you think that that's where life can thrive more easily, and thus can you know,

can be anything, can it can experiment evolutionarily. But in fact, it seems that part of what's going on in the easier to live in environments is a lot of things want to live there, so there's a lot of competition. So it's putting a lot of pressure on the things that do live there to you know, make it really count. So they have to optimize and they like, you can't be just a little bit slower than the other fish, so you've all got to be these fast swimming fish.

So there's actually less room for evolutionary diversity.

tripod fish. Though this is a little confusing because the word tripodfish is also used to refer to more generally a bunch of fish in this family, but sometimes this species of fish in particular is called the tripod fish. These are also sometimes known as spiderfish or the tripod spiderfish. I actually first came across this because of its taxonomic relation to the grideye fish that we talked about in Part two. The tripod fish is also part of that fish's family, the family ibnopidy.

ocean floor. The tripod fish is commonly known as a demersal fish, meaning a fish that lives on or directly above the bottom substrate of a lake or sea. And there are organisms that you'll see gliding directly over the sediment. But what I like about the tripod fish is that it looks like it almost daintily does not want to sully its fins in the mud, and it uses these biological stilts to stand a few of its body lengths

up above the bottom. For a formal description of the species, I dug up a report published in the journal Pacific Science from nineteen ninety by a pair of researchers named Anthony T.

twenty meters on the southern slope of Maui. The specimens were identified by the features that characterize the species, very long produced pelvic and caudal fin rays, a uniformly dark body, an unpigmented dorsal fin, an undivided pectoral fin held upright with the rays extended straight, and lower caudal fin base canted anteriorly. So tripod fish are predators that sit up on their stilt legs facing into the current, waiting for

prey to come near them. And there's something very interesting about these ste because when you see them standing up on the stilts, and it kind of suggests that these stilts are I don't know that they're stiff, like they look like they would have to be in order to support your weight like that, like the legs of a stool. But an interesting thing that Jones and Sulac note is that while these rays, these things appear stiff, when the fish is standing up off the bottom, suddenly the fish

will get disturbed. Maybe it'll get kind of disturbed by like the arm of the of the remote vehicle, and it'll suddenly swim away. And then these things like lose their their rigidity and they become flexible. They just appear to glide behind the fish. So it's kind of interesting

imagining how they do that. Maybe some sort of internal fluid pressure mechanism or something, but interesting to wonder how But instead of relying on site to catch pray, like we were just talking about, the tripod fish seem to rely on sensitive elongated pectoral fin rays. Look up pictures

of these things. They will be perching on the bottom on the three legs, and then they'll have what looks like two little antennae coming up off of their heads like or like devil horns, and you can see these devil horns poking up into the water like they're kind of feeling around in the water for something. And it

seems that is what they're doing. They're detecting prey animals drifting along with mechanical and perhaps gustatory sensations, and then these these fins help guide the prey to the mouth.

into each other and so forth. The other thing is that bioluminescence in this in this realm where light from the surface either takes on this this strange, you know, less intense form, or is just gone altogether. Bioluminescence light created in the deep by organisms. This becomes this whole

place of interaction and weaponization. And I thought it might be fitting for us to go ahead and roll through all of the known uses for bioluminescence and fill in some examples for categorizations that we haven't talked about already. So the University of California at Santa Barbara has an excellent website about bioluminescence called simply the Bioluminescence web Page.

I think it's been been around for a while at this point, but it's got some just great It's has some great visual breakdowns of the different categories of bioluminescence

and you know, some examples. Uh. And they break everything down into three broad categories of function, offense, defense, and a third category that includes a single function and that's made attraction slash recognition swarming queue, and so I thought that would be a good place to start, and then we'll get into defense and offense, which includes some categories

that we've touched on already. So when it comes to made attraction recognition and swarming queues, they mentioned several examples and possible examples for this category, because the thing about bioluminescence, well, first of all, I should stress that these categories tend to not be like one hundred distinct like so many examples will. We'll check off the box for multiple categories.

I mean, such as the power of bioluminescence down there, there's a certain amount of drift and what it's actually achieving or seems to be achieving for any given species. And then, of course the other factor is we're still figuring out exactly what role bioluminescence has in any given species, especially when, of course, when we get into deeper species and rare species that we just don't know much about.

But I'd say the most interesting example they bring up here, and probably you know key too our discussions, are the lantern fish of the family micto Fia day and they're found in more than two hundred and forty different different species. I've seen the species count as high as three hundred,

and they're found worldwide. They're very abundant. According to the twenty eleven Encyclopedia of Fish Physiology, they make up sixty percent of all deep sea fish biomass, so, as you might imagine, that means they are very much on the menu for anything that is eating anything that's preying on

fish in the deep ocean. They themselves, however, feed on zooplankton. Now, most species practice diurnal vertical migration, in which they stick to the depths of the bathoplegic zone during the day, and then they'll venture upward into shallower waters at night

to feed. And as their name implies, lanternfish. They boast photophores that are certainly thought to help provide camouflage, breaking up their silhouette against filtered sunlight from above to protect against predators beneath, but some researchers hold that they may use these lights to communicate with each other as well.

According to the Woodshole Oceanographic Institute quote, the arrangement and flashing pattern of these running lights are unique to each of the two hundred and forty five plus species of lantern fish, which suggests that they're not just used to camouflage the animals, but also to communicate. However, other sources I've looked at, such as that twenty eleven Encyclopedia of

Fish Physiology, kind of downplay the possibility of a community roll. Okay, Now, there are other examples of organisms in the ocean that use their lights or seem to use their lights for communication. The ostracods, for example. These are tiny crustaceans noted for their blue or green bioluminescence. This is thought to aid and communication and identification as well. So again that's one way that bioluminescence can be used to sort of like say hey, I'm here, this is what I am, and

so forth. But getting more into these like the offensive and defensive array, getting into the drama and conflict of predation, first the offensive use of bioluminescence, rolling through the different

subfunctions that are outlined by the Bioluminescence website. First of all, luring prey we discussed a prime example of this with various deep sea angler fish create a light draw in other fish that are drawn to that light because it might mean a meal, or it might mean a chance to breed, and then you gobble up your prey when

they get close. Now the next example, this one, This one's really interesting lure with external light, And this is one I hadn't thought as much about, but it should be common sense to us denizens of the sun and the moonlit world, and also a world where we've created a lot of external illumination sources. If you don't create your own deep sea light as a lure, might you

depend on other species for illumination. Sperm whales, for example, may possibly seek out communities of bi iluminescent plankton, not to eat them themselves, but to watch for the plankton's defensive displays of bi iluminescence, which signals the presence of a predator, and this in turn would invoke the whales attack and Megamouth sharks may also employ this tactic. But I'm to understand that in either case we don't know for sure. I think this is this is still very

mention in the realm of a of a hypothesis. Now here's the next categorization. Stun or confuse prey. It's thought that some squid may use bioluminescence to stun or confuse the prey species that they're after in addition to communication.

In a two thousand and seven paper published in the Proceedings of the Royal Society, b Observations of wild hunting behavior and Bioluminescence of a large deep sea eight arm squid Teningia Dana, authors Kupadira at all right that the squid's intense light emissions quote may work as a blinding flash for the prey as well as a means of illumination and measuring target distance in an otherwise dark environment. Oh yeah, and they may also use their lights to

deter count competitors and adversaries of the same species. So again, once you get into the use of this bioluminescence again that often it's multiple things. There may be multiple purposes in play here. But these are big squid, by the way, reaching lengths of one point seven meters or five point six feet, and their photophores, they're light emitting parts here,

are enormous, often compared to fists or lemons. They're positioned at the ends of special arms, and they have what's described as like an eyelid like membrane, like a black membrane that closes over it. I included a photo here for you, Joe. It does indeed look like a great pale pupilis eye at the end of a squid arm.

or confuse the prey. But the other thing is why didn't I think of this before perhaps using it as illumination or way of measuring target distance, so essentially using it like a flashlight to illuminate prey so that it can better be located, the same way that if you were trying to like catch a chicken running around at night, you would need like to shine a flashlight at it to chase.

like a fighter plane too. Like you can really I have an easy time imagining this thing like zooming in on its on its target and then flashing them and then moving in for the kill, and then doing more flashing to say, hey, I'm at work here, everybody else, stay away, I've got yeah, all right, And that leads into the fourth example here of offensive bioluminescence usage, and

that's to illuminate prey. So this particular species Tananingia dana may cover this example as well, but flashlightfish and dragonfish are also really good examples. So dragonfish of the Stomidae family, especially barbled dragonfish, are deep sea apex predators of the bathlevilegic zone. Absolute icon horror shows with needle teeth that

look super intimidating on a poster. I actually had a listener write in, I think on Discord saying yes, I had the same poster, and I think maybe it was like a national geographic poster that had all these fish on it, a lot of deep sea fish. But this particular listener, also as a kid, didn't know how big these were. These guys tend to be like fifteen to twenty six centimeters in length, but there's still apex predators

in their deep environment. They use their bioluminescent barbeles to attract prey as well as communication, it seems, but the species of loose jaw dragonfishes can produce red light via far red e midi photophorce to illuminate prey as well as help detect the red lights of their kin. According to Woodshole, they gain their red light abilities via their diet of copopods, and this is the only family of

fish that can, via this method, produce red light. They're kind of like, it's like they're wizards of the deep that have a school of magic that most other fish do not have. But they're also of course competing with each other, so they want to know what the other wizards are up to. Included a photo here of Specimen Joe. Everyone else should look these up as well. Dragonfish as

because their jaws are crazy. They have these like big hinge jaws that you know, it looks like some sort of mechanical device that might be employed here.

It's flashing throws them off at least makes them hesitate. But also this bleeds into another defensive categorization, and that is what is generally called the burglar alarm. So when these particular marine plankton or other organisms such as some jellies flash defensively against predators, it also illuminates them and raises the profile of the attacker, So it raises the stakes.

They're essentially saying, yes, you can continue to attack me, slash us, but you will do so in the spotlight where other predators can see you.

the infernal vampire squid. When threatened, they'll eject not a pseudomorph of ink, so not like like a cloud of ink shaped like their body, but rather a cloud of bioluminescent mucus.

this off. Apparently first they grasp their predator, like they sort of like go to their predator, but then they release part of the arm that is in contact with the predator it's glowing, and then they make their escape. It's kind of like jump in there, grapple your attacker, but then leave them your arm and make a break for it.

Now because you have to remember, first of all, these sorts of tissues may continue to glow for hours, and many of these creatures are largely translucent, so eating a glowing meal could mean everyone will know you're there, they see the glowing meat inside you, and predators may notice.

warning colorization. This one overlaps with several examples. The glow is a warning of all the bad things that could potentially happen to the predator if they eat or try to eat the prey, and it also can communicate the old standby that we're familiar here on the surface world as well, and that is the warning, Hey, I'm not taste or maybe I'm toxic. I'm not good to eat, so stay away from me. Look how bright I am?

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