Instant Genius - Deep sea creatures - Everything you ever wanted to know about... the deep sea with Dr Jon Copley

Episode Date: November 9, 2020

Our guest this week is Dr Jon Copley. Jon is a marine biologist, specialising in the deep sea. He went on the first mini sub dive to the world’s deepest hydrothermal vents, 5km down on the ocean floor, and also took part in the firs minisub dives to 1km deep in the Antarctic. Jon is also a science communicator and writer, who worked as a science advisor on the iconic BBC series Blue Planet II. He is also an associate professor of ocean exploration and public engagement at the University of Southampton. In 2019, he also published fantastic book called Ask an Ocean Explorer which tells you all about the ocean in 25 questions. Over three quick-fire episodes, Jon tells BBC Science Focus managing editor Alice Limpscombe-Southwell about the bizarre life found on the ocean floor, the habitats where they thrive, and what it's like to explore the deep sea in a submarine. Hosted on Acast. See acast.com/privacy for more information. Learn more about your ad choices. Visit podcastchoices.com/adchoices

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available in print and in several digital formats throughout the world. Find out more at sciencefocus.com or look out for us in your app store. Hello and welcome to the everything you wanted to know about podcast from the team behind BBC Science Focus magazine. I'm Alice Lipscomb Southwell, the managing editor at BBC Science Focus. For this series, we sourced the most in-demand questions from Google, our listeners, and a few from the team itself,

and put those questions to an expert to help you get to grips with the most important ideas and discoveries in science, in short, concise, 30-minute doses. This time, we're talking to Dr. John Copley. John is a marine biologist, specialising in the deep sea. He went on the first mini-sub dive to the world's deepest hydrothermal vent, five kilometres down on the ocean floor, and also took part in the first mini-sub dives to one kilometre deep in the Antarctic. John is also a science communicator and writer who works as a science advisor on the iconic BBC series Blue Planet 2. He is an associate professor of ocean exploration and public engagement at the University of Southampton,

and last year he published a fantastic book called Ask an Ocean Explorer, which tells you all about the ocean in 25 questions. In this episode, John talks to us about some of the bizarre species that live in the depths of the ocean, the beauty of bio-loonessence and the wonderful ways that some species have evolved to hide, hunt and survive in the inky depths. I'm John Copley. I'm a marine biologist. I work at the University of Southampton in the UK,

and I specialise in trying to understand the ecology of deep sea environments. So that's the 65% of our world that's underneath water more than 200 metres deep. And it's a dark, hidden world, that we perhaps don't think about much in everyday lives, though our everyday lives are inevitably connected to it. And to study it, you need to get down there with some technology and find out what's living where and what's going on. And that's basically been my career over the past 25 years. That's brilliant. So, I mean, the vast majority of people, even if they haven't obviously been down

into the deep sea, they generally know that it contains a lot of weird life. So why exactly is deep sea life so strange? That's a very good question. Deep sea life seems strange to us because a lot of the conditions and processes in the deep sea are not the same as the ones, you know, in the everyday world around us. And that's why we notice that things are different. Every organism faces sort of trials of life, finding food, avoiding becoming food for somebody else, finding a mate and often finding and setting up home somewhere. And in the deep sea, we see lots of what to us are weird and wonderful ways of solving those challenges. And that's what makes deep sea life seem so bizarre to us is the conditions that it's coping with. The way that those challenges present in the deep ocean are different to what we're familiar with in the everyday world above the waves.

Okay. I mean, we're also taught a primary school that life needs sunlight to survive. You draw your little food webs when you're six years old. He starts with sunlight and then it goes to plants and then animals eat them. But obviously in the deep sea, it never sees a beam of sunlight. So how exactly does life survive down there if there's no light reaching there? So light in the deep ocean. Light actually goes a little bit further into the ocean than I think we tend to realize. So there isn't enough light for algae to thrive through photosynthesis.

beyond 200 meters, and that's in the very clearest sort of open ocean waters. But sunlight still filters down a little bit further than that, and possibly down to as far as about a thousand meters deep when the last photon from the sun is quenched by the seawater. So that's our first zone in the deep ocean that we go through when we visit the deep ocean, and it's what we call the twilight zone, because there's still very faint downwelling light down to that thousand meters. Now, in some places, it's much shaller than 1,000 meters, but there's still this twilight zone at the top of the deep sea. But it's not bright enough for algae to photosynthesize.

So everything in the deep sea, twilight zone, and then the zones beyond that, which are forever beyond the reach of the sun's rays, everything is depending on either food that is ultimately sinking from above, a food chain that starts with algae, thriving in the sunlit surface waters, or in a few very special places in the deep ocean, we do have places where there are bacteria that can thrive on chemical energy sources, either gushing or leaching out of the earth's crust. So, yeah, we can have some very different

food chains in the deep sea. And that's really opened our minds to what's possible for life. How can life be supported in lots of different ways? How might life? be supported, you know, elsewhere in our solar system, you know, further out and so on, where sunlight would be much fainter. Because there have been discussions about that, haven't they? Places like Europa, where there isn't as much sunlight, but they could be using this sort of bacterial life rather than you're relying on algae or something like that. Yeah, so we have this process in the deep ocean called chemosynthesis.

And not just in the deep ocean, actually. We now know that it happens in, you know, in dark mud, in estuaries and in lots of other wonderful places as well. But it's life starting with chemical energy instead of sunlight energy. And yeah, that's opened our minds to the possibilities of life in places like Europa. What you need is an energy source. And in the deep sea, sometimes that's a volcanic sort of energy source that's driving the system. So anywhere where you've got liquid water and you've got potentially volcanic activity, you could have similar systems to some of the habitats we get in the deep ocean where life thrives.

Oh, it's super exciting, though, isn't it? Because like you say, you always think, oh, you need that sunlight to survive. And then you've got this stuff right down the bottom of the ocean that's just, yeah, getting on flying about it. Well, we have to be a little bit careful because the animals that we see in these hot spots in the deep ocean. And, I mean, the most famous place where life thrives from these chemical energy sources in the deep ocean are these hydrothermal vents, these hot springs on the ocean floor.

And we see them in TV documentaries nowadays. and there's this tremendous abundance of animals thriving around them. All of those animals need oxygen to survive. They're animals, just like we are, okay? We need oxygen. The oxygen that they need comes from deep water that flows down into the deep ocean from the poles and it takes the oxygen from the atmosphere at the poles. How does that oxygen get into the atmosphere?

That oxygen has built up in the atmosphere thanks to plant life, photosynthetic organisms over a long period of time building up oxygen in the atmosphere. So there are some microbes that can survive with chemical energy sources and no oxygen at deeps events. That's the kind of analogue we might look for elsewhere in the solar system. But for the animals, although they're not getting their energy from photosynthesis at the base of a food chain, they are nevertheless dependent on photosynthesis because otherwise they wouldn't have any oxygen.

So what animal lives the deepest then? What's the deepest dwelling animal we found so far? Well, we know that animals live all the way down to the bottom of the very deepest trenches. And we've known that since the 1950s, in fact, when they were first dredged up from more than 10 kilometres deep. Now, what types of animals live down there is a very interesting question. We know there are crustaceans, shrimp-like animals. There are some ones at the bottom of the deep trenches called giant. amphipods and they're quite interesting. They're normally an amphipod. They're sort of sand hoppers you get on the beach and they can be the size of a large flea or whatever and a few

millimeters long. Down at the bottom of the deep trenches, they can be, you know, getting on for 10 centimeters long. So they're much bigger down there. They survive just fine down at the bottom of the trenches. We get animals like sea cucumbers living down there as well, which are actually related to starfish that we get on our rock pools as well. Interestingly, what we don't get at the bottom of the deep trenches are fish. So the deepest known fish is just over 8,100 metres deep. And we don't think fish go all the way to the bottom of the deep trenches because of biochemical reasons, of the way that their cells actually cope with some of the problems

of pressure. So it would have to be just, yeah, invertebrates. So we'll be able to, you know, hack those really extreme. conditions then? So there's probably a zone at the very bottom of the oceans that could be as you know as deep as two kilometres where it's invertebrates only. But there aren't that many trenches that go that deep. So so in terms of actual volume of ocean that's beyond sort of eight kilometres deep, it's not that much globally. So you personally have been in submersibles and you've gone to the bottom of the oceans. What's the sort of coolest or weird list?

weirdest creature you've personally seen when you've gone down there? Oh, that's a tough question. What's the weirdest thing I've seen in the deep sea? I would have to say it's something called a benthic cyphonophore, which is a bit of a mouthful, but it's actually a colony of organisms. So it's this shaggy mass of individual polyps. And it looks like a monster from,

old-fashioned Doctor Who, you know, when they didn't have such big budgets for special effects. So it's, you know, it can be a shaggy looking body that's sort of three feet tall with these polyps sort of hanging off its, off that central body, a neck that it can extend like an old fashioned car aerial can make longer and shorter with a float on the top that makes it look like a head. Oh my gosh. and it can push this thing up and down in the water above it. And then trailing behind it, very, very long tentacles that trawl the seafloor. And it drifts in the very gentle ocean currents at the seabed.

It drifts across the bottom of the ocean like a ghost. And it ratchets its float head up when it encounters a rock or whatever. And then it pulls its body up and sort drifts over this. dangling these tentacles behind it. And it is completely bizarre. It's really weird. And it's a colony. You know, that's the other thing. It's not one animal. It's actually a colony. There are polyps there for feeding and there are polyps there for reproducing and modified polyps that form that float structure. And yet all somehow coordinated and the ones that do to feeding are feeding the bounty of that food with the rest of the colony. So, you know, it's an incredible superorganism.

if you like. And how old was an organism be that was down there? Because can't some things in the deep ocean live for just sort of hundreds of years? And we think, you know, some of the deepest dwelling sharks like Greenland sharks, they could live for hundreds of years, potentially, just because it's such a stable environment and it's cold down there. Some things can live for a very long time in the deep ocean. So yeah, we have things like Greenland sharks that can live for many centuries. And you can age them from, you know, various ways of a bit like tree rings that can give you a reliable age estimate for these animals. And some of them are older than the United States of America as a country, which is incredible.

There's one animal has lived through all of that history, if you like, that's been happening up here. Because often the pace of life, for some deep sea animals, the pace of life can be slow if it's a scavenger. And in between meals arriving from above in the form of carcasses of dead things that sink to the ocean floor, its metabolism is ticking over very slowly to save energy. And so they can be very slow pace of life and they can be very long lived. The same is probably true of those benthic cyphonophores that I love, because actually the colony can keep renewing itself. So individual polyps might live and die, but they'll be replaced.

So the whole colony could be actually really quite old. It's not been the same polyps necessarily the whole time through. But yeah, if you think of the whole thing as the organism, it could also be very old. So when you talk about some of these animals that you can age them as well, so how exactly would you go about that? Can you look at their bones or when they wash up, you can have a look at them, figure out how old they are? For some animals, you need some sort of structure that has what we call growth increments. So just like tree rings, you need something that you can use to actually count the time. of the clock. So for some types of fish, there's a bone in their ear where you get rings growing

every year, every season or whatever, and you can use those to count and then age them. And in fact, you can do even more than that. You can even look at the elemental composition of the different rings. And that tells you about the conditions in which the fish was living when that ring was forming, even things like, you know, the temperature of the water. So you can actually get the sort of history of that animal's life out of that tiny little bone from the area as well. Well, that's really interesting. So when you got all this deep sea life and it's evolution, you say everything's sort of evolving and connected together. So do we have quite a long fossil history of these deep sea animals? Because, I mean, obviously if a lot of them are invertebrates,

sometimes it can be hard for them to fossilize. So have we got a good record there? The problem we have with fossil record of the deep sea is actually plate tectonics, the system by which the plates of the earth's crust move around. Because, of course, the oceans, what's at the bottom of the ocean is what we call ocean crust. And ocean crust is created at mid-ocean ridges, where two plates are being rifted apart. Basically, the plates are riding on convection cells in the earth's mantle. And in some places, those convection cells are pulling plates apart. a bit like a rift valley forming. And that's what we get at these things called mid-ocean rid-ocean ridges,

where the plates are being pulled apart. And that means molten rock, magma, ultimately lava, is welling up, erupting at the seafloor and making new ocean crust. What happens at the other end, though, of those plates, the other side of those plates, where they collide with plates carrying the continents, well, often there they get what we call subducted. So they get pushed back down into ultimately the Earth's mantle where they are melted and recycled. So anything that dies, sinks to the bottom of the ocean, gets buried by the sediments, building up on top of it.

You might think, great, you know, it might fossilize, give us fossil record. Well, it rides the plate as the plate moves gradually from the Mid-Ocean Ridge, and you get that sediment settling on it and potentially fossilizing things. But then it gets to the subduction zone, and it gets pushed back down into the Earth's mantle and melted. And that means that fossil record is destroyed. Now, very occasionally, we get situations where this process goes wrong, where subduction doesn't happen. The motion of the plates kind of flips and a slab of what it would normally be ocean crust going back down into the mantle gets slapped onto a bit of continent and can be preserved.

And that's where we might get fossil records of deep ocean dwelling things. And then occasionally, we also have environments that were ocean and now are. not where we might see that preservation, but it's rarer than you might think. And so in terms of fossil record, we can do quite a lot by comparing different genetic sequences of organisms, figuring out their tree of life, tracing that back and with some idea of rates of mutation and rates of evolution. And we can sometimes calibrate those, what we call call upon molecular clocks with certain events, you know, when two oceans were finally cut off as a continent and crashed into another continent and separated them,

and we know the timing of that from the rocks on land, we can ultimately piece together a sort of a family history with some dates and then look at the patterns of evolution in the ocean. Oh, it's tough, though, isn't it? You think, oh, it would just be so nice if you could just get a nice fossil coming up on land. I'll tell you what everything was. Oh, yeah. So on a sort of similar-ish subject, I suppose,

So we've got giant squid, which live in the deep sea. We know they exist because they've been pulled up in sort of fishermen's nets. But we know they're rarely seen. So are there any other elusive animals out there that we're pretty sure they exist, but we just haven't really ever seen them? There are lots of elusive animals in the deep sea. The giant squid is pretty iconic. So, I mean, it's got a history going back a long time.

Pliny the Elder, writing in the first century, gave an account, second-hand account, of some guards of some fishponds on the coast of what's now Spain, apparently fighting off some sort of giant octopus-y squid thing that came and tried to raid these fish ponds. They presented its body to their boss. They said they fought it with tridents. I have to suspect that it might have just washed up there as we know these things too. And they then said, oh yeah, we fought it, boss. You know, and we deserve a bonus. But anyway, Pliny put down this account describing the animal and describing suckers of its tentacles and the overall size of it. And it's quite a good description. So these things have occasionally been washing up naturally dead on beaches and mystifying

people through the centuries. More recently, yes, getting caught in fishermen's nets. And we have actually seen them alive now in the deep ocean. So the first pictures were in 2005 and then video a few years after that. But there are other big squid out there. So the giant squid has a cousin, if you want to think of it like that, called the colossal squid. About the same length probably as adults, so up to 12, 13 metres long,

from the very tip of the pointy bit at the kind of tail end to the very tip of the longest arms. The colossal squid about the same size, probably a bit meatier, though a bit, sort of beefier and tougher. And, yeah, I mean, that's been elusive for a long time. And we've known about colossal squid since I think the species was described in 1925 from baby specimens that were fished up. What's fun is you can have a guess at how many undiscovered species

of large animal, sea monster, if you want to think of them in those terms. how many are out there from looking at the rate at which people have been finding new ones. So this is quite a nice little mathematical trick. If we'd seen all the big animals in the ocean, then it doesn't matter how much we carry on looking. We're never going to find anymore. The rate of discovery will flatten off. We won't keep finding new ones.

If there are still plenty out there, then we're likely to keep finding them fairly regularly as we carry on going looking. So you can basically plot, you know, all of the discoveries and descriptions of large animal species in the oceans over time. And you get what we call a collector's curve, a discovery curve. And it gradually starts to flatten off. And when we've seen them all, it will be completely flat. Okay. There will be no more new discoveries.

It hasn't flattened off yet. And when it's close to flattening off, you can then fit an equation to it to predict how many more are out there. Where will it flatten off? and the estimate is of the order of probably another 10 or so, 10 to a dozen that are probably out there that we haven't even seen yet. So there are still discoveries to make. There's still big things out there. I mean, the top pop culture one you hear about a lot is Meglodon, isn't it? People say, oh, Meglodon, it's still out there. But I know that marine biologists say, well, probably not.

I'm afraid definitely not. No. Okay. Now, now, you know, and when I say definitely not to Megalodon or to mermaids or to these other things that capture our imagination, and I think it is wonderful that the deep is this place of mystery that captures our imagination, people say, well, hang on, if you haven't explored it all, how can you say for sure that it isn't out there? Well, what we haven't yet seen has to fit with our understanding of how the oceans work. Okay. Otherwise, we're wrong about everything. And I don't think we are wrong about everything because we can make very good predictions as to what lives where and we understand ocean currents and we understand the geological history and the ecology and all that kind of thing. We would have to be wrong about all of that for these things to exist. So, you know, I'm not even going to say probably not. I will say definitely not. And there are several reasons for that. Conditions in the ocean when Megalodon went extinct a little over

two and a half million years ago. Conditions in the ocean were really quite different then than they changed. The food source for them, the types of whales they were feeding on changed. And for a shark that big, they would be wide roaming to get all the food they need to support them as this super apex predator. And we know they were wide roaming because we find their teeth all over the place. And so if they were out there today, they would have to be equally wide. roaming. We would have seen them by now. And unlike the movie The Meg, which I do enjoy,

they can't unfortunately be lurking at the bottom of deep trenches like they were in that movie, because sharks, all the types of sharks, they can't live deeper than about 4,000 meters deep in the ocean for biochemical reasons. They have a depth limit. So they're not hiding in the bottom of the trenches, unfortunately, either. So also talking sharks, again, but many animals in the deep sea, so you've got sharks, you've got squid and snails, quite a lot of them will sort of create their own light. And again, this is a really wide-ranging skill they've got. So how do they do this? They're all doing it in the same way, or if they've got different methods of doing it? Animals creating their own light in the deep sea, it's actually

probably the most widespread form of communication on our planet. And again, because it's happening in the deep ocean out of our immediate sight. You know, we tend not to think of it like that. But yes, there's lots of animals creating light, using it for lots of different purposes. And they are making light in different ways as well. Sometimes they are able to make it themselves in their own cells. Quite often, they are doing it in partnership with bacteria. And they might have organs that house bacteria inside them, inside their tissues and so on, in order to produce light from that organ. And they use light for lots of different purposes,

and it does depend a little bit on where they live. So the basics are some animals will use light to hunt. So this is the other thing about we think of the deep sea, is not eternally ultimately dark. There is light down there. There is this what we call bioluminescence, light created by life. There isn't sunlight beyond 1,000 meters, but there's still light in the form of bioluminescence. So some animals are making light to hunt down there.

And this is also why a lot of deep sea animals do have eyes. People often are surprised. There's dark out there. How come? Like some of these cavefish. They haven't lost their eyes. Well, many of them are visual predators still. Creating light to hunt, search lights to illuminate their prey or lures to attract their prey is the other way of doing it.

and ambush their prey. Some of them are using light to evade predators, to confuse predators, to create a distraction so they can get away. So we've got that kind of arms race going on down there. They're also creating light to attract and signal to potential mates as well. So there's communication with members of the same species through light as well. So those are kind of the basics of it. And then in that special zone where there's still very faint light coming from above, not bright enough for photosynthesis, but still some faint downwelling light, what we call the twilight zone, well there they also, that's actually where we get most bioluminescence, 90% of the animals living in that zone make light, and many of them are using it for camouflage. And what they're doing is they have lights on their

bodies, often on the underside of their bodies, that match the faint light that's welling down from above. So that breaks up their silhouette. It means they don't cast a sharp shadow because a lot of their potential predators are beneath them looking up for shadows of prey, passing overhead in the faint light that's coming down from above. So it's all about trying not to cast a shadow and trying to spot shadows of potential prey. And one of my favorite examples of this is a fish called the hatchet fish. And it lives in that twilight zone. It's called a hatchet fish because its body is is very, very narrow from side to side across its body. So it's bit like an axe head, hence hatchetfish.

So it's very thin across its body. And that itself is to try and avoid casting much of a shadow, but not having much of a profile in cross-section like that. And we've known for a long time, and you can see this if you ever watch original BBC Blue Planet First series from 2001. They showed how the hatchet fish does this. But the hatchet fish has got these light producing organs on its underside.

And where it lives, there's faint blue downwelling light. And those light organs produce faint blue light that matches that light coming from above. And that enables it to do this kind of vanishing trick and break up its silhouette and just sort of blend into that background, when seen from below, which is where a lot of its predators are. So it can kind of vanish in that way. Now, we've known about that for a long time, but only very recently have researchers figured out, well, that's fine. It's got these glowing organs on its underside, but its eyes are on its head and they're looking out sideways. How does it know if it's getting it right? How can it tell if it's light organs on its stomach, you know, its underside are producing the right, you know, intensity of light to do the vanishing trick? Well, people have recently shown that it has another light organ that shines into its eye. And it doesn't project forwards like a searchlight or anything like that. It only shines into its eyes, presumably wired up with the ones on the fish's underside. And it's like a reference light.

So the fish can see this little light in the corner of its eye. Compare it with the light that it can see around it for the depth where it's living and make sure the two match in order to get the vanishing trick right. So I think that's incredible. And that's only very recently been shown. And then the other reason I love the hatchet fish is this is great. So this is how it does this vanishing trick for predators that are living below it, looking up for shadows. Yeah, but what about the predators that are swimming alongside lighting up prey with searchlights? How does it hide from them? Well, again, much more recently, when the vanishing ship trick was shown in Blue Planet 1, we now know that when it comes to predators hunting from the sides, the hatchet fish's skin has got these tiny structures in it that are what are called phoenixing. tonic crystals. And there are a particular structure that scatters light. So if a predator with a search lightes it from the side and lights it up with that, instead of getting a really bright

reflection back from the sides of the fish and therefore knowing that there's a hatchet fish, tasty morsel, the light gets scattered around the hatchet fish's body. So it's almost like a kind of invisibility cloak bending light around the fish's body. So it doesn't reflect so much back to a predator. So it is fantastic. It's, You know, that's almost like the predator of science fiction, isn't it, with kind of invisibility cloak, bending light around it, plus those other tricks. You know, this is the ingenuity of nature that we see in the deep ocean that fascinates us. I've saw something the other day as well about there's a fish that's been discovered. And I think that it's a deep sea fish again, and it's as black as Vanta black.

Good, yeah. Next on my list, good. Yeah, so other ways you can hide from predators. Yeah, if you're a hatchet fish, maybe you can bend it. light around them. The other way you can hide from predators, of course, is by making your skin really non-reflective, really absorbent of light. Now, things that appear black to us in the everyday, they actually probably reflect about 2% of the light back to us. We still see them as black, but they're not as black as they could be. They're not absorbing all of the light. And so again,

recently a team of researchers have found fish in the deep ocean that have little granules of dark pigment under their skin arranged in a way that is ideal for absorbing as much light as possible. And they absorb all but half a percent of the light that falls on them. So, you know, they are really, really black, ultra black, in fact, is how they describe them. And so that means the range at which they can be detected by a predator searchlight is actually much, much shorter. You know, they're just not seen by predators until they're right on top of them, which costs less chance to encounter a predator, more time to escape, that kind of thing. So again, these amazing adaptations.

And then the other neat trick we get in the Twilight Zone, the other way you can avoid casting a shadow is to make your body see-through, make yourself transparent. you know, like the invisible man of science fiction, which when you think about it, I mean, that's incredible because you don't just make your skin see-through. You've got to make all your internal organs, you know, how do you make a see-through animal? That's an incredible adaptation. And we see that that has evolved independently in several groups of animals. There are giant amphipod crustaceans that live in the Twilight Zone forever swimming, you know, not crawling around on the seabed or whatever, that are translucent, entirely translucent.

like that, there are squid that are entirely. They're called glass squid because they look like blown glass. And again, see-through to avoid casting a shadow. So you could be ultra-black, you could be transparent like the invisible man, you could have an invisibility cloak like the hatchet fish. So if you've got a fish that are transparent or translucent, then if they're making themselves see-through, then have they got, is their blood sort of translucent as well then and all their organs inside their bodies? Yeah, they're amazing, you know, not perfectly see-through. And in fact, the ultra-black fish are probably more camouflaged when it comes to light

shining on them than these translucent things. But, yeah, and a problem that if you're going for the see-through solution, a problem is, well, what happens if you swallow a meal that's a glowing animal? Now it's sitting in your see-through stomach and it's glowing out. advertising you to predators. So some animals have actually got pigmented guts. And another of my favorites is something called the blood belly comb jelly. And it's so-called because it has a red pig, it's seethru in its body, but it has a red, red pigmented gut.

Now, red generally appears black in the deep sea because there aren't natural sources. is there are very few natural sources of red light. Red light gets filtered out by the seawater quickest. So, you know, none of the wavelengths that are getting down into the twilight zone are red. There are a few deep sea predators that make their own red light. And that light probably can't be seen by a lot of their prey. A lot of deep sea fish aren't sensitive to red wavelengths of light in their eyes. But so, so if you want to make a cheap black pigment that isn't as complex as ultra black and so on,

which is energetically expensive to create. If you can make a red pigment in the deep sea, it will appear black to most things. So that's why actually there's a lot of red color down there. A lot of the deep sea shrimp are red, things like the blood belly comb jelly. Its belly is red because red is a cheap way of appearing black down there. So people also say to me, how come things are colorful down there when it's dark? Why are these things coloured?

And sometimes it is for that reason. Red is actually a form of camouflage in the deep sea. Sometimes things are other colours just because it's the color of the thing their bodies are made of. If their exoskeleton is made of a particular compound and it has a color, then it will be that color. It doesn't mean they're using it to advertise or to signal necessarily. When we get down to animals that live at the seabed, so not the ones that are floating up in the twilight zone and then the midnight zone beneath it, but we get actually down to the seabed,

how do animals make a living there? Well, lots of different ways. There's this sort of constant, gentle, we call it marine snow, which is a wonderfully poetic description, but essentially it's poo and snot and remnants of small living things from the ocean above that sink their way down into the deep ocean. And they form this kind of detritus that slowly rains down on the seafloor. But it's organic matter. So it's potentially got. food value for anything that can eat it. So one way you can make a living on the ocean floor is just to plow your way through this stuff that's raining down from above. And we see quite a few animals that do that. So these sea cucumbers do that. They sort of plough across the ocean floor,

eating all the time, pooing all the time, leaving a trail behind them, extracting whatever nutrition they can from that stuff raining down from above. But occasionally there can be richer food parcels arriving from above if something bigger like a fish or even really big like a whale or whatever dies and its body naturally sinks to the ocean floor. So we've also got animals that are scavengers of those larger what we call food falls. But of course those are further apart in space and further apart in time than that constant rain of detritus. So there it's about finding the next meal. And we see some amazing adaptations amongst those scavengers for literally sniffing out a food full, their next meal. So they'll have sort of search strategies crossing the

prevailing ocean current to detect odour plumes of dead things that arrived at the seabed and then swimming up that odour plume to home in on it and make a meal of it as a scavenger. And then, of course, the other solution you've got is to be a predator as well to just eat one of these other animals. So, and there's a couple of ways you can go about being a predator. You could be an active hunter. So zooming about, you know, maybe with searchlights or whatever, hoping to encounter prey and then strike and take that prey. But that's energetically quite costly.

So a lot of the predators we see down at the ocean floor are what we call ambush predators. So they will sit and wait. So they're not expending much energy. Their metabolism is ticking over slowly. but they've got, again, amazing senses, particularly things like a sort of extended sense of touch. They might be able to detect any disturbance in the water some distance away and then strike. So a nice example of those are these things that we call tripod fish. There are lots of different species of tripod fishes, and they have modified fins,

what we call the pectoral fins that come off the chest and modified tail fin. These are all lengthened so that they are like the three prongs of a tripod, and they will sit, resting on those three fins, hence tripod fish, on the ocean floor, and they'll sit there quietly, not using much energy, and they'll be pointed kind of up into the current, and they'll be feeling for and sniffing for anything that's within striking distance, basically. So we see a lot of ambush predators down there as well. Well, that was brilliant, so we're going to wrap it up there for today. In the next episode, John and I are going to delve deeper into some of the intriguing habitats and niches that exist in the deep ocean, including trenches, ridges, whale falls and hydrothermal vents.

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