A trip to the twilight reefs

Down beneath the waves, where the light starts to fade, there's an ecosystem scientists don't fully understand. About a decade ago, some researchers left structures in this mysterious world and let them grow encrusted with life. Now they're pulling them back up again and unwrapping them like scientific presents. Guests: Luiz Rocha, ichthyology curator at the California Academy of Sciences, along with Johanna Loacker, Lynn Bonomo, Chris Meyer, Sarah Tweedt, Tito Monteiro da Cruz Lotufo, Emily Rutkowski, Yara Tibirica, Daniel Eisenhauer, Terry Gosliner, and Chrissy PiotrowskiFor show transcripts, go to ⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠vox.com/unxtranscripts⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠ For more, go to ⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠vox.com/unexplainable⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠ And please email us! ⁠⁠⁠⁠[email protected]⁠⁠⁠⁠ We read every email. Support Unexplainable (and get ad-free episodes) by becoming a Vox Member today: ⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠vox.com/members⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠ Thank you! Learn more about your ad choices. Visit podcastchoices.com/adchoices

• 0:00Speaker 00

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• 0:39Speaker 01

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• 1:11Speaker 02

  Okay. Okay. Ready? Yeah. Objectives, proficiency, and get some arms.

• 1:17Speaker 03

  On a break, beautiful day last May, I was standing on a boat floating in the waters of the Republic of Palau. I was watching several people preparing to scuba dive.

• 1:29Speaker 02

  Depth, 145.

• 1:31Speaker 03

  Beneath our boat, there was a gorgeous coral reef ecosystem, a turquoise world that was teeming with life. But these divers were planning to go beyond those shallow reefs, go deeper.

• 1:45Speaker 02

  It's a team assignment. Deep, plus deep.

• 1:48Speaker 03

  Recreational scuba divers are often going 18 meters down, max, maybe 30 or 40 if they have extra certification. But two of these divers were planning to go down to 45 meters, and the other two were going to go even further, about 100 meters into the deep.

• 2:04Speaker 02

  Are all divers mentally prepared to dive? Absolutely.

• 2:09Speaker 03

  And they were doing all this, preparing to descend so far, because they wanted to retrieve some scientific structures they'd left down there, down in a mysterious, understudied world known as the mesophotic coral ecosystems, which is a mouthful, so I will call them deep reefs for short. But they're a world that one of the divers, a zoologist named Luis Rocha, has a lot of questions about. And the hope is that these structures will help him and others get some answers, help them put together some of the pieces of a very puzzling ecosystem that they fundamentally do not understand.

• 2:50Speaker 04

  Let the games begin.

• 2:52Speaker 03

  So, this is unexplainable. I'm Brad Pinkerton. And today on the show, how do you solve a puzzle like the deep reefs?

• 3:17Speaker 03

  Luis Rocha started exploring the ocean early.

• 3:19Speaker 05

  So I grew up in a small town in coastal Brazil. Oh, it was small when I was growing up, not so small now, but always going to the beach every weekend. And I always had this interest and attraction to the ocean. So I always wanted to go deep. I always wanted to go to a place where people don't go to very often or never been to before. I wanted to see things that nobody has seen before. So I started with tide pools and then snorkeling and then scuba diving and then scuba diving a little deeper and then deeper and deeper and pushing the limit of depth. And I was always very excited about discovering new things.

• 3:56Speaker 03

  So it makes sense that Luis, as part of his work for the California Academy of Sciences, explores these mysterious deep reefs. But what is a deep reef, exactly? The term can be used to describe ecosystems that go way down into like the ocean's abyss, so places with no sunlight at all, sometimes thousands of meters down. But for the purposes of this story, we're going to use deep reef to refer to a world that's a little closer to home. So a few tens of meters from the surface down to about 150 meters. And to understand that world a little better, let's pretend we're Luis for a minute and do some of our own exploring.

• 4:39Speaker 03

  First, we will go somewhere with deep reefs, let's say Palau for now, and then we'll dive. And for the first 10, 20, 30 meters of our descent, we'll be in bright, clear waters, and we'll see the kinds of coral reef you might be more familiar with. These are complex ecosystems full of crackling crustaceans and stinging anemones and darting, flashing, munching fish. And at their heart, they have hard corals, so these little animals that secrete the calcium carbonate structures that make up the reef itself. But these corals partner up with photosynthesizing algae that need sunlight to thrive.

• 5:20Speaker 03

  And as we go deeper, down to 40 meters, 50, 70, 100, the temperature will start to drop and the sunlight will start to fade. It actually fades so much that people sometimes use the term twilight reef to describe this ecosystem. And that dimming light means that there is less and less opportunity for photosynthesis at these depths. But it does not mean that there is no life down here. Instead, we're descending into a world of animals that can survive with less light: sponges and sea squirts, mollusks and crustaceans, bryozoans, even corals that have adaptations that let them make the most of low light.

• 6:07Speaker 05

  And the deeper portion of reefs is really, really the unknown portion. So almost everything we know about coral reef biology, about coral reef ecology, about coral reef evolution comes from science done in the top 30 meters of reef. Anything between 30 meters and 150 meters is really, really unknown because it requires a different kind of diving. It requires technical diving. It requires much bigger time commitment from the scientist, and it's riskier. Even from the human perspective, it's risky for the divers.

• 6:40Speaker 03

  People have used remote operated vehicles and submersibles to explore the deep reefs, but those can be expensive. And if you drop a camera down there, it might not be able to capture the really small species or the hidden ones. And so deep reefs are just trickier to study than their shallow neighbors are. And there's lots left to learn.

• 7:03Speaker 05

  Whenever we go somewhere, the first thing we find is new species. I'm talking about fish here, which is one of the most charismatic organisms you can find in a reef. But if we started looking at sponges and gorgonians and crustaceans and mollusks, I mean, there's so many new species. It's like the most basic thing in science you can do is describe a species, and it's the first step that kind of starts the chain to do everything else. But even that, even at that level, those ecosystems are unknown.

• 7:35Speaker 03

  If you imagine the project to understand shallow coral reefs, so the coral reefs that we know more about, like a whole bunch of people all collaborating to try and solve a 10 million piece puzzle, that puzzle, obviously, still has a lot of gaps. We have lots of questions about coral reefs. But humans have been collecting pieces of that puzzle and snapping them together for a very long time now.

• 8:02Speaker 05

  We probably have like eight to nine million pieces, and of those, I'd say five million are assembled.

• 8:09Speaker 03

  So if you squint at the shallow coral reef puzzle, you can at least get a pretty good picture of what's there, right? Who's eating whom and how species interact and what gaps you might want to focus on next. If you try to compare that to the deep reef puzzle, though, Luis told me the puzzle itself might actually be a bit smaller, just because less light can mean less diversity. But he can only guess at how many pieces this puzzle has right now, and we've pulled up fewer of those pieces to look at.

• 8:41Speaker 05

  So it's a lot, it's a lot less information to go with. So there's so many big questions that need to be answered.

• 8:46Speaker 03

  Luis wonders about things like, what's the main energy source for everything down there in this dimmer light, right? What does the food chain look like? Or how do things evolve to live down at these depths? And then, how similar are they to the shallow ecosystems? Or how different? How are they affected by climate change? These are some of the big, basic questions you might ask, but also...

• 9:14Speaker 05

  In some ways, we don't even know what questions to ask. When we go to ecology and evolution, we could ask the same questions as we do for the shallow reefs, but that's kind of not the same. We really only know what questions to ask after we have a baseline understanding of what the ecosystem is. And for deep reefs, we don't know that yet.

• 9:35Speaker 03

  So for years now, Luis has been gathering bits of basic information on these reefs, been diving down, exploring at these depths, collecting fish, which are his specialty. But the problem with diving is that even with specialized equipment, it has limits. As you go down, gas gets pushed into your tissues, kind of slowly turning you into the human equivalent of a carbonated soda. And the deeper you go, the more pressure there is, so the faster you get carbonated or nitrogenated, really. So if you want to descend to 100 meters to explore the deep reefs, you get gassy very fast.

• 10:16Speaker 05

  We have a very, very short time, and by short time, I mean five minutes, six, seven minutes.

• 10:21Speaker 03

  What can you do in five minutes?

• 10:24Speaker 05

  Usually, because it's so limited and we have so much gear, each diver has one task. So if my task is taking pictures, I come down with my camera and I take as many pictures as I can. If my task is doing transects, I do two transects and we start moving up. If my task is collecting fish, I collect two or three fish and we start moving up.

• 10:47Speaker 03

  That moving up can then take hours because he has to let the gas in his tissues out sort of bit by bit, kind of like you'd slowly turn the cap on a shaken up soda bottle to keep everything from exploding out too fast. Sometimes he's able to do more science on the way up, but other times, he has had to try and entertain himself with like an iPad in underwater housing.

• 11:10Speaker 05

  I tried playing Angry Birds in it. It was very, very, it made me very angry because I could never get, the touchscreen is not very precise. I could never get the ball to go the right way. But it was a good, it was a good pastime.

• 11:27Speaker 03

  It is obviously not super efficient to try and explore something in five-minute bursts. And about a decade ago, Luis started to explore another option, too.

• 11:38Speaker 05

  There was a method of sampling a lot of biodiversity on the reef that was pioneered in the early 2000s, and it's called autonomous reef monitoring structures.

• 11:50Speaker 03

  ARMS, or ARMS for short.

• 11:53Speaker 05

  It's PVC structures consisting of PVC plates that are stacked together, and the plates have a standard size. They're stacked together the same way, so you can build each structure, each one of these structures is identical to the other.

• 12:07Speaker 03

  ARMS were developed, basically, to study underwater ecosystems in a standardized way. So if you pick up an encrusted rock from a reef, it'll be different from other encrusted rocks on other reefs. It'll be unique. ARMS are built to be not unique, very similar and very comparable. So you take what looks like a little nine-floor hotel the size of a toaster oven, these sort of stacks of gray PVC plates, and you bring however many of them you want, three, 13, 34, whatever, down to various spots that you want to study or compare. Then you secure them in place, and you leave them for a while.

• 12:50Speaker 05

  As soon as you drop any kind of clean structure on a reef, it starts getting colonized by larvae of everything around it, sponges, gorgonians, corals. And then, because there's a lot of hiding spots between the plates, so between the floors of the hotel, they start getting colonized by shrimp, by mollusks, by acidians, by anything you can imagine in the ocean. And it becomes this stable, diverse, like, mini reef, if you will, packed with a lot of biodiversity that would be very hard to collect all at once in any given reef.

• 13:30Speaker 03

  Years later, you come back, you scoop the ARMS up, and then you can study this mini reef that you've made. You can see and touch and smell things, sample them, photograph them, send everything in for DNA analysis, whatever you want. To Luis, this seemed like a solution to some of his frustrations, a way to really get a long look at these deep reefs instead of the brief glimpses he was getting from diving. And so between 2016 and 2018, he went out to four different locations: Palau, Guam, the Marshall Islands, and French Polynesia. And in each place, he, along with a group

• 14:11Speaker 03

  of other researchers, dove down to put a bunch of ARMS at 10, 50, and 100 meters. And then, they waited. They actually waited a little longer than Luis would have liked because he needed funding, and COVID messed up some plans. So almost a decade passed. But eventually, at long last, some private funders agreed to underwrite the retrieval of the ARMS that he'd left. Clear. Which takes us right back to where we started, when Luis and his fellow divers had just jumped into the water to retrieve some ARMS. What they found after the break.

• 14:56Speaker 01

  This episode is brought to you by Michelob Ultra. Good times mean competitions between you and your friends, like seeing who can throw some pigskin the farthest or rush the field the fastest. Winner gets an Ultra. Because it's not just a Superior-like beer, it's also giving fans superior access to their favorite sporting events. Superior is worth playing for. Visit michelobultra.com/superioraccess to enter. Enjoy responsibly. Copyright 2026 Anheuser-Busch InBev Michelob Ultra Beer, St. Louis, Missouri.

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• 16:36Speaker 08

  Just crossed over into the Twilight Zone.

• 16:43Speaker 09

  I think one of them is coming.

• 16:54Speaker 03

  Over the course of several days, I watched a whole team of people pull ARMS out of the deep reefs of Palau. So a boat full of divers, including Luis, would go down into the deep and actually get the ARMS. But then, because the deep divers had to stay at depth a long time and decompress, they would pass the ARMS up, kind of relay style, to shallower divers, who then brought them up to a second boat, full of scientists from lots of different institutions.

• 17:22Speaker 09

  They're a boat length away.

• 17:24Speaker 03

  The shallower divers would emerge, and they would pass a small, clear tub to the people waiting on the boat.

• 17:31Speaker 10

  You got it?

• 17:32Speaker 09

  Yes.

• 17:33Speaker 03

  And inside that tub was an ARMS, sort of cube-like stack crusted over with red and orange light.

• 17:42Speaker 02

  Looks like a goodie.

• 17:43Speaker 03

  Some ARMS were a little sparser, others were almost fuzzy with organisms.

• 17:48Speaker 11

  Lots of sponges on this one. Neatly.

• 17:51Speaker 03

  But each one was quickly transferred from the small tub into a big, black storage bin full of water.

• 17:57Speaker 02

  Seal.

• 17:58Speaker 03

  And then, once all the ARMS were ready to go, usually around two of them each day, we'd take off back to the lab. Andiamo, andiamo. Because they wanted to start documenting everything while it was as fresh as possible. We would motor back through aquamarine waters, past little islands covered in green forests. And eventually, we would pull into the Palau International Coral Reef Center, or PCCR, which is an institution devoted to coral research that was letting these scientists use their facilities for this work.

• 18:31Speaker 09

  All are out.

• 18:33Speaker 03

  And you might imagine that the main focus here would be new species, right? Unknown things. Instead, I watched the researchers racing to just document everything they found, new or old, in as much detail as possible. It's like a well-oiled, cheese-it-fueled, sort of beautiful disassembly line.

• 18:56Speaker 09

  Do you have another size wrench?

• 18:59Speaker 03

  Step one was just breaking down the ARMS. Two researchers from Cal Academy named Johanna and Lynn were often helping with this part. And they would pull on bright red, elbow-length rubber gloves. They kind of look like the gloves they use for insemination of cows. And then they would open up a bin and use a wrench to pull the stacks of nine gray ARMS plates apart.

• 19:22Speaker 12

  Which one?

• 19:23Speaker 03

  This one?

• 19:24Speaker 12

  Okay. Let me, I'm on.

• 19:25Speaker 03

  Sort of one thick square plate at a time.

• 19:28Speaker 12

  I think I got it. Hold on.

• 19:30Speaker 03

  Okay. Each plate, as they lifted it out, was almost like a modernist painting. So picture like a little gray square canvas, but covered in swatches and streaks and swirls of red and orange and yellow and green. And they would place each of these works of art into a little wire rack in a new tub of seawater. And then, when all nine plates were in, they would pick the tub up.

• 19:55Speaker 13

  Great.

• 19:56Speaker 03

  And haul it over to a cool, air-conditioned lab nearby, before then returning to the bin that they had disassembled the ARMS in.

• 20:07Speaker 11

  And now, back to the sounds of slashing hook.

• 20:10Speaker 03

  They would sieve through the water in the bin, and then they would hunt through those sieve sediments for anything moving. Lynn told me it was kind of like a game of I spy. So imagine that, but with sea slugs and worms and lots of crustaceans.

• 20:25Speaker 09

  Crab, some shrimp. Shrimp. Shrimp. Shrimp. Chumbo shrimp.

• 20:32Speaker 03

  And then meanwhile, some of the other members of the team had set up stations to process what they called "the furniture of the plate." So everything that was not moving, that these various creatures had been crawling around on. And it began with the big picture, literally.

• 20:48Speaker 13

  So we are going to start late photographing.

• 20:52Speaker 03

  Chris, a Smithsonian curator who directs the Global ARMS Program, was the guy in charge of this big picture photography.

• 20:59Speaker 13

  Oh, you know what? This is kind of an important part. This piece here needs to be plugged into the computer. If you forget to do that, not much happens.

• 21:07Speaker 03

  Once he had things properly set up, he would take a series of high-resolution pictures of each plate, and then those were all stitched together into sort of one beautiful, complete image.

• 21:17Speaker 13

  So this is the photo mosaic, fun part.

• 21:23Speaker 13

  It's kind of like nature's art.

• 21:25Speaker 03

  When Chris was done photographing what the front and the back of the plate.

• 21:28Speaker 13

  Are you guys ready?

• 21:29Speaker 03

  It would move on to a trio of samplers who were sort of the next step in the arms disassembly line.

• 21:36Speaker 11

  So what we're doing is we're looking for every unique thing, which we call morpho species. And we're trying to get some representative tissue samples from all of these things so that we can sequence the DNA and match the DNA to the organism.

• 21:53Speaker 03

  Sarah, who's also from the Smithsonian, and she was in charge of grabbing and photographing samples of soft corals and other kind of encrusting creatures on each plate.

• 22:03Speaker 11

  You know, this, this red one here is distinct from this one. These, these may be the same species. This one, let's see.

• 22:15Speaker 03

  Next to her was Tito from the University of Sao Paulo. And he was doing basically the same thing Sarah was doing, but for these animals called tuniquids. So things like sea squirts, which he told me are actually our closest invertebrate relatives.

• 22:30Speaker 04

  They've just decided to take a different route on evolution and become simpler rather than complex. So they can solve all their problems very, very easily.

• 22:40Speaker 03

  This sponge is... Across the table from both of them, Emily from the University of Hawaii was sampling sponges.

• 22:47Speaker 14

  Guys, this sponge is so cool.

• 22:48Speaker 03

  Kind of poking and prodding them, cutting them up.

• 22:51Speaker 14

  Sometimes when you cut them, they'll have like, there's this one that has like a strong garlic smell when you cut it. So you gotta make sure to smell them as well. Yes. You gotta ask them what they do on the weekends, you know? It matters. It matters.

• 23:08Speaker 03

  Emily also spent a lot of time just showing me sponges. So she showed me a sponge that sparkled with little silver filaments and then this thin flat sponge that felt dry underwater, a little sponge like a sandcastle. All part of her campaign to convince people that sponges are cooler than we give them credit for.

• 23:28Speaker 14

  You know, I do, I convert one person and then they convert one person. It's like a triangle, you know?

• 23:33Speaker 11

  A pyramid scheme. Teach them how to fish.

• 23:35Speaker 03

  Mostly, though, all three of these researchers were just in an ongoing conversation with each other as they tried to identify the obscure, colorful lumps on these plates.

• 23:46Speaker 04

  Well, you already did, right?

• 23:48Speaker 14

  Yeah, it's on the edge.

• 23:50Speaker 04

  It's a sponge.

• 23:51Speaker 14

  No.

• 23:53Speaker 03

  When I first got to the lab, every time someone started to ask what something was, I kind of expected them to say, "I've never seen this before. It's a new species."

• 24:03Speaker 14

  Tuniquids, a sponge.

• 24:04Speaker 03

  But before these researchers could even begin to wonder about something like that, they had to answer much more fundamental questions.

• 24:12Speaker 14

  It's firm? Yeah, it's not a sponge.

• 24:16Speaker 03

  Like if something was a sponge or a tuniquid or what?

• 24:19Speaker 04

  So it may be a tuniquid, but it's really small. We couldn't see the siphons. So that's why I wouldn't call tuniquids whatever they are.

• 24:29Speaker 03

  And while all this was happening, the people playing I Spy would be trying to identify the animals they were finding. They would carry creatures in cups over to a researcher sitting in the corner by a microscope. Earlier on, this was Yara, later Daniel, both from the University of Guam.

• 24:51Speaker 08

  That's the family of Pogurop suudae, which literally means fake hermit crab.

• 24:56Speaker 03

  And then people would also bring creatures out to another room where these two zoologists from Cal Academy, Chrissy and Terry, were sitting next to a whole bank of microscopes ready to identify things.

• 25:06Speaker 15

  Oh, it looks like it's another one of these Scalibragmatidae, the maggot worm.

• 25:14Speaker 03

  Really, though, everyone in the lab was contributing to this sort of overall project of trying to figure out what was what. Is that a marginaled? It was this constant course.

• 25:24Speaker 02

  Wow, he's cool. What is that?

• 25:26Speaker 13

  Like, who built that? Oh, that's an Australopod. I think it's an amphipod.

• 25:29Speaker 11

  Did you write down 1570 is Caprelidae?

• 25:33Speaker 13

  Oh, it's not a amphipod. It's not a, it's not a decapod. I think it's a polyp.

• 25:37Speaker 14

  I think this is the hard text.

• 25:39Speaker 13

  This one's Labraliniata.

• 25:42Speaker 03

  Sometimes they could identify things with specificity.

• 25:45Speaker 11

  Oscarrelle. Oscarrelle, for sure.

• 25:49Speaker 03

  Other times, they were documenting things they were maybe less familiar with. So at the end of this particular project, they had close to 3,000 specimens. And they're still processing the data, so the estimates are changing. But at last check-in, around 3% had species name tags. A little less than 20% were a step up from that. So they had a genus, but not a species. And then many, many others were more broadly identified by family or subfamily or at higher taxonomic levels.

• 26:22Speaker 15

  Take a look.

• 26:23Speaker 03

  And that's why they were trying to grab samples of, of everything and document those samples so well, so that down the line, people with more time and more access to genetic tools might be able to pin down exactly what these things are.

• 26:37Speaker 13

  Did you guys get this brachypod looking, this green sponge up here? See the brach right in the middle?

• 26:43Speaker 14

  No, I don't have that at all.

• 26:44Speaker 13

  Can you grab it?

• 26:45Speaker 14

  Okay, I'm gonna get a tweezer.

• 26:46Speaker 13

  Grab some tweezers. I haven't seen that one.

• 26:49Speaker 03

  There was one guy, this guy named Terry, who's a nudibranch expert. So he studies a type of sea slug. And he really could look at certain sea slugs and basically make the on-the-spot call about whether he thought they were least likely to be new species to science pending genetic confirmation. And on the first day that I was following the team, they actually found several species that he thought were new.

• 27:15Speaker 09

  It's your lucky day.

• 27:17Speaker 16

  What have you got?

• 27:19Speaker 09

  A third nudibranch Johanna found it.

• 27:22Speaker 16

  How exciting.

• 27:24Speaker 03

  At one point, Johanna found a, a little sea slug. It looked sort of like a small yellowish oval with little horns and a branching veiny pattern.

• 27:35Speaker 16

  Very cool.

• 27:36Speaker 03

  Lynn carried that slug over to Terry, and he was pretty quickly able to guess what, what family it was in. Look at it.

• 27:42Speaker 16

  Look at it. I think it's a Discodorid of some sort.

• 27:46Speaker 03

  Okay. But he waited a bit for the, the slug's gills to open up, and then he pulled out this document on his computer. It's a book he's been revising that's full of pictures of nudibranchs. He basically just started scrolling through like an incredible number of multicolored slugs. This very loud machine started running in the background as Terry was scrolling, but eventually he landed on one slug in particular.

• 28:12Speaker 16

  Okay, so it's similar to that, and it has that sort of netwik-like pattern, but it's distinct. So my conclusion is that until we have some genetic evidence that it's a third new species, most likely.

• 28:38Speaker 03

  Terry told me he felt fantastic about this, and he seemed quite pleased. But he wasn't like, "Everyone stop what you're doing, you know, come see the new species." And earlier that same day, when I was talking to him about a different sea slug that he also believed to be a new species, I even said to him...

• 28:59Speaker 02

  You seem very blasé about a new species.

• 29:03Speaker 16

  Well, I'm not blasé. I'm excited. It's just, you know, another day's work, but I still...

• 29:15Speaker 09

  So do you want this here?

• 29:18Speaker 16

  What?

• 29:19Speaker 09

  This is for you, here.

• 29:21Speaker 16

  What is that?

• 29:23Speaker 09

  A limpet, I believe, that Chris just sent over. Do you want it here?

• 29:27Speaker 03

  To be fair, these arms took a long time to unpack and work often stretched late into the night. So nobody really had too much time to dwell on anything. But also, over the days, it kind of struck me that many people on the team were definitely excited about the idea of seeing something new, but they seemed just as excited about relationships between species, whether or not they were new.

• 29:53Speaker 13

  Oh, Tito, is this our, is this our Medusa guy?

• 29:57Speaker 03

  Chris and Tito, for example, were interested in a tuniquid they found that was full of snake-like worms. And then when I walked into the lab one day, several people told me to go look at something known as a pom-pom crab.

• 30:08Speaker 14

  He's so cute.

• 30:11Speaker 03

  Which turned out to be a tiny yellow crab holding purple anemones in its claws.

• 30:16Speaker 17

  Red to the feeling itself.

• 30:20Speaker 03

  Sarah, meanwhile, seemed especially excited about creatures that mimic other creatures. So one night at 1:12 a.m., she showed me what she called "the frosting on the cake of the day."

• 30:31Speaker 11

  So these are ovulates.

• 30:33Speaker 03

  These were bright red sea snails. But Sarah was so jazzed about them because she also had the bright red octocorals that they lived on and sort of looked a lot like.

• 30:43Speaker 11

  And, and the mimicry is, is so precise that that is a polyp on a coral. It's a papillae on the, on the snail.

• 30:52Speaker 13

  This is a polyp on a coral. That's the coral.

• 30:56Speaker 03

  In another conversation with Sarah, she said something that's kind of the key to all of this for me. So the researchers had just gone through some final steps in processing the arms. They had scraped the plates clean with a paint scraper, ground everything up in a blender before pouring it into a very fine mesh bag. And Sarah was in the process of doing something that some people called "milking the turd", which was removing the water so that the remaining material could be sampled and sent off to be analyzed for DNA.

• 31:31Speaker 03

  And while she did this, I was talking to her about my puzzle piece idea. So this idea that we have very few pieces from the deep reefs. And this was a project to bring up more. And she said to me,

• 31:42Speaker 11

  Oh, yeah. So to be fair, we have had, we have collections in museums, for instance, from exploring expeditions. And people would dredge and pull up weird MISO to deep things.

• 31:58Speaker 03

  They would grab individual puzzle pieces from the deep twilight reefs. But those pieces weren't really in context necessarily. The beauty of something like the ARMS project isn't just pulling up pieces. It's more like that thing where you open a puzzle box and some of the pieces are still stuck together. So if you lift them out gently, you get not just a few pieces, but how they connect.

• 32:25Speaker 11

  Something really powerful is taking note of associations. Like who likes to live with who? You know, what likes to live on what? What gets along, what doesn't seem to get along? You know, I think that's particularly exciting to document because it's not always easy to keep organisms together where they live when you're collecting them. And I think that ARMS allows you to do that in a really nice way.

• 32:51Speaker 02

  Which is why you were so excited at 2 AM.

• 32:53Speaker 11

  Which is why I was so excited at 2 AM.

• 32:56Speaker 03

  That idea about individual puzzle pieces versus the connections between them feels connected to a conversation I had with Luis. So I was talking to him about the idea that deep reefs are a really hard puzzle. And I asked him why he would even want to work on a puzzle that was so hard and had so many gaps.

• 33:20Speaker 18

  It's the reward at the end of it. Which means if it's a hard puzzle, at the end of it, the reward is always bigger.

• 33:26Speaker 02

  But you're not, like, in our lifetimes, will we assemble the deep reef puzzle?

• 33:34Speaker 18

  No, no, we will not assemble the puzzle. No, but we will generate some good pieces for the next generation to assemble.

• 33:43Speaker 02

  So you might not even get the reward of the really hard puzzle.

• 33:47Speaker 18

  No, no.

• 33:50Speaker 03

  At the time, it felt like a little bit of a contradiction in his thinking, honestly. But listening back to my conversation with Sarah and with other researchers, I realized I was thinking about Luis a little like an individual puzzle piece and not as a piece connected to other pieces. My name is Johanna Loacker. Obviously, I am aware that science is a process that involves a large number of people all working together. I'm Lynn Bonomo. But there's still this impulse to focus on one individual and their contributions to a project. I'm Emily Rutkowski. So I expected for this story to focus mostly on Luis, maybe one other researcher in the lab. I'm Sarah Tweed.

• 34:33Speaker 03

  But when I arrived, I quickly realized that if I focused on any one person, I'd kind of lose the plot of how the ARMS were brought up and disassembled. I'm Chrissy Kietrowski.

• 34:44Speaker 16

  My name is Terry Gosliner. My name is Matt Schmidt.

• 34:46Speaker 03

  I'm Lauren Scheinberg. And the project of processing these ARMS won't end with this group.

• 34:52Speaker 05

  So my name is Luis Rocha.

• 34:53Speaker 03

  From here in Palau, some of the samples collected will go back to the California Academy of Sciences, others will go to the Smithsonian.

• 35:00Speaker 13

  It's Chris Meyer.

• 35:02Speaker 03

  The University of Sao Paulo and elsewhere.

• 35:04Speaker 04

  My name is Tito Monteiro de Cruz Lotufold. Short version, Tito Lotufold.

• 35:11Speaker 03

  Last year, they brought up the ARMS that they'd left in Guam.

• 35:14Speaker 04

  I'm Daniel Eisenhower.

• 35:15Speaker 03

  And the University of Guam kept many of those samples in their collections.

• 35:18Speaker 17

  I'm Yara Chivirisa.

• 35:21Speaker 03

  And these samples will be available for people to study. So other scientists will pick through the organisms that the team have collected here. They'll identify things more precisely. They'll work out what's new and what's not new, but also how things connect.

• 35:35Speaker 19

  So I'm Susanna Beer. I'm a postdoctoral fellow with the California Academy of Sciences.

• 35:40Speaker 03

  Susanna, also known as Susie, was one of the divers, and she works with Luis. She's already analyzed some of the Guam samples to understand how much the species change as you go deeper. The Palau samples will let her sort of check that work and see if her findings hold up here, too. And there is plenty more work to be done on that question and on all the other big questions that people have.

• 36:08Speaker 03

  So sure, yes, Luis is not going to solve the very hard puzzle of these deep twilight reefs all alone. And it almost certainly will not be solved in our lifetimes. But to me at least, there is something kind of rewarding and exciting about the idea that there's so much work left to be done and that it will take so many people working together to do it.

• 36:34Speaker 11

  What is this bunch?

• 36:35Speaker 04

  Oh, this is Derek.

• 36:36Speaker 11

  Yeah, start. I'm going to play the Nudibranch songs. You Nudibranch songs? You have much better. What is this? What's a Nudibranch song?

• 36:47Speaker 02

  Sorry, Yara has pulled up a video that's called Psychedelic Sea Slug Dance on YouTube.

• 36:57Speaker 02

  You don't need to see. Get just a listen.

• 37:01Speaker 20

  The Nudibranch started way long ago in the ocean deep below. It was the latest craze in town. It was the greatest dance around. The Nudibranch branch, the psychedelic sea slug dance, dance. Do the Nudibranch, Nudibranch, it's the latest, it's the greatest. Come on, baby, do the Nudibranch dance.

• 37:24Speaker 03

  This episode was produced by me, Byrd Pinkerton. It was edited by the wonderful Lissa Soapp and by Jorge Just. Thanks, Jorge and Lissa, for everything. Joanna Solotaroff and Meredith Hadnath both also weighed in on aspects of this episode. Meredith runs the show and Joanna is executive director. Christian Ayala did the mixing and the sound design. Melissa Hirsch checked the facts. Noam Hassenfeld does our music. And the Nudibranch song you're hearing is "The Psychedelic Sea Slug Dance" by Will Thompson.

• 38:01Speaker 03

  Miles Yuwo, Chris Shertleff, and Davon Howard helped me with gear. Valerie Schenkman, Alex Kohls, Kareem Korea, and Sally Helm are the fact that some corals can fluoresce. Thanks always to Brian Resnick for co-creating the show with me and Noam. Thank you to Megan Ely at Cal Academy for all the work that she put into coordinating my visit. Thank you to Clara Diaz for taking the time to help me understand the mesophotic. And thanks to Shannon Bennett for her time as well. A big thanks to every single one of the people who are working on this Palau project, who walked me through what they were up to. But an especially big thanks to Johanna Loacher for taking so much time, both before

• 38:44Speaker 03

  my trip and during my trip, to explain things to me. If you, our listeners, have thoughts about deep reefs, or about the mesophotic, or your own stories about exploring the ocean, please reach out. We are at [email protected]. We'd also love to hear your ideas for show topics. If you'd like to support the show and the journalism that Vox does, we would love it if you would become a member. It's very easy to do. Just go to vox.com/members and you'll get access to all of Vox's journalism, but also know that you are supporting all of Vox's journalism. For those of you who have emailed us to let us know that you signed up because of Unexplainable, thank you. And thanks also to those of you who have left us a nice review on your podcast platform

• 39:29Speaker 03

  of choice, or just told someone in your life about the show. You are the best. Unexplainable is part of the Vox Media Podcast Network, and we will be back very soon with another episode about everything that we do not know.

• 39:50Speaker 21

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• 40:19Speaker 22

  At Edward Jones, we believe rich is about taking care of what gives your life meaning. That's why your financial advisor personalizes your plan to help you preserve your progress and create something that lasts. Let's find your rich. Edward Jones. Member SIPC.