A trip to the twilight reefs

Summary

Unexplainable – "A Trip to the Twilight Reefs" (August 5, 2026)

Episode Overview

This episode plunges listeners into the enigmatic world of "twilight reefs" or mesophotic coral ecosystems—deep, dimly lit coral reefs found between 30 and 150 meters beneath the ocean surface. Host Fred Pinkerton joins a research team in Palau as they retrieve autonomous reef monitoring structures (ARMS) from these rarely studied habitats. The episode explores why these twilight reefs are so mysterious, the technical and logistical challenges of researching them, and the collaborative, puzzle-like nature of scientific discovery in the deep sea.

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Main Discussion Points & Insights

1. What Are Twilight Reefs? (03:42–05:49)

• “Deep reefs” (mesophotic) are coral habitats beyond the well-studied shallow reefs (10–30 meters), extending down to 150 meters.

• Twilight refers to the limited sunlight that reaches these depths, creating a very different ecosystem from shallow reefs.

  Fred Pinkerton:

  "As we go deeper... 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." (04:56)

  • Life persists, but organisms must adapt to survive with less light: sponges, sea squirts, mollusks, unique corals.
  • These habitats are vastly understudied due to extreme technical difficulties and danger in surveying them directly.

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2. The Unknown Frontier of Deep Reefs (05:53–09:21)

• Luis Rocha (California Academy of Sciences) describes how almost all scientific knowledge of reefs comes from studies above 30 meters, leaving the mesophotic zone a "blank space" on the map.

• Technical diving is required to reach these depths, making research riskier, more expensive, and more logistically complex.

  Luis Rocha:

  "Anything between 30 meters and 150 meters is really, really unknown because it requires a different kind of diving...It's riskier even from the human perspective." (05:53)

• Even the most basic level of science—describing new species—is barely begun here.

  Luis Rocha:

  "Whenever we go somewhere, the first thing we find is new species...Even at that level, those ecosystems are unknown." (06:49)

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3. Studying the Unknown—Arms and Constraints (09:21–14:25)

The Challenge

• Deep diving for research is extremely time-limited. Luis and his team get only a 5–7-minute window at 100-meter depths due to safety constraints and decompression needs.

  Luis Rocha:

  "By short time, I mean five minutes, six, seven minutes." (10:02)

• Each diver is given a single task: take photos, measure transects, or collect a couple of specimens.

  Luis Rocha:

  "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 collecting fish, I collect two or three fish and we start moving up." (10:11)

ARMS: A Long-term Solution

• Autonomous Reef Monitoring Structures (ARMS) are clumps of stacked PVC plates (like a “nine-floor hotel”) placed on reefs to be colonized by a diversity of marine organisms over months or years.

• ARMS are standardized for comparability between sites and allow researchers to sample and study reef biodiversity at depth without constant human presence.

  Luis Rocha:

  "As soon as you drop any kind of clean structure on a reef, it starts getting colonized by larvae...It becomes this stable, diverse mini-reef, if you will, packed with a lot of biodiversity that would be very hard to collect all at once." (12:37)

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4. Retrieving and Processing the ARMS (16:45–30:36)

The Retrieval (16:45–19:01)

• Multiday dives in Palau: deep divers retrieve ARMS, pass them relay-style to shallower divers, then to a waiting support boat.

• ARMS, crusted in life, are immediately transferred to seawater storage, rushed to the Palau International Coral Reef Center.

  "Some ARMS were a little sparser. Others were almost fuzzy with organisms." (17:48)

The Lab Assembly Line (19:01–26:27)

• The team dons elbow-length gloves and carefully disassembles each ARMS, one plate at a time, preserving delicate layers of species.

• Plates are photographed from multiple angles (mosaics) and sorted for further study.

  Johanna Loiker:

  "So this is the photo mosaic fun part. It's kind of like nature's art." (21:22)

• Researchers pick off, catalogue, and sample every unique organism—identifying "morpho species" and collecting tissue for DNA barcoding.

  Emily Rudkowski:

  "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." (21:41)

• The sampling line includes experts in many specialties: tunicates, sponges, crustaceans, and others, all contributing their expertise.

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5. The Excitement and Frustration of Discovery (24:56–30:36)

• Many specimens are completely undocumented—a sea of “what is that?” moments.

• Only ~3% of specimens have a precise species name tag; about 20% are classified to genus; the rest are more broadly identified.

  Fred Pinkerton:

  "At the end of this particular project, they had close to 3,000 specimens…At last check in, around 3% had species name tags. A little less than 20% were a step up from that...Many, many others were more broadly identified by family or subfamily or higher taxonomic levels." (25:54)

• There are memorable moments of possible discovery—such as finding several likely new nudibranch species (sea slugs) on the first day.

  Johanna Loiker (re: a new sea slug discovery):

  "How exciting." (27:27)

  Terry Gosliner (nudibranch expert):

  "My conclusion is that until we have some genetic evidence that it's a third new species, most likely." (28:18)

• The excitement is tempered by the understanding that most work goes into foundational identification and documentation work, not just headline-grabbing new species.

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6. Interconnected Puzzles and Generational Science (31:00–35:40)

• The value of ARMS isn't just in species discovery, but in capturing their relationships and associations—the living links between creatures as they actually exist on the reef.

  Sarah Tweed:

  "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...ARMS allows you to do that in a really nice way." (32:30)

• The metaphor of the “puzzle” recurs: deep reefs are a gigantic, mostly unsolved puzzle, and the work is about gathering pieces—and, crucially, how pieces fit together.

• Luis Rocha is motivated by contributing pieces to a puzzle future generations will finish:

  Luis Rocha:

  "It's the reward at the end of it if it's a hard puzzle, and at the end of it, the reward is always bigger...No, we will not assemble the puzzle, no. But we'll generate some good pieces for the next generation to assemble." (33:25–33:47)

• The project is inherently collaborative, relying on teamwork across disciplines, backgrounds, and institutions, underscoring the communal, generational nature of science.

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7. Humor and Human Moments (10:56, 23:33, 36:39)

• Luis tries to pass time decompressing by playing Angry Birds on an underwater iPad:

  "It was very, very. It made me very angry because I could never get...the ball to go the right way." (10:56)

• Emily converts others to her enthusiasm for sponges:

  "I convert one person, and then they convert one person. It's like a triangle, you know, a pyramid scheme." (23:33)

• The episode ends lightheartedly with the team watching a “Psychedelic Sea Slug Dance” video:

  "The nudie brand started way long ago in the ocean deep below...Dance to the nudie, nudie, nudie branch..." (37:06)

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Notable Quotes

• Luis Rocha:

  "Everything we know about coral reef biology ... comes from science done in the top 30 meters of reef. Anything between 30 meters and 150 meters is really, really unknown." (05:53)

• Fred Pinkerton:

  "If you try to compare that to the deep reef puzzle, though, Luis told me the puzzle itself might actually be a bit smaller...But he can only guess at how many pieces this puzzle has right now." (07:55)

• Emily Rudkowski:

  "You gotta make sure to smell them as well." (23:03)

• Sarah Tweed:

  "Something really powerful is taking note of associations like who likes to live with who..." (32:30)

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Key Timestamps for Segments

| Timestamp | Segment | |---------------|-------------| | 03:06–05:49 | Description of twilight/deep reefs and their unique biology | | 05:53–06:49 | Discussion on lack of knowledge and risks of deep reef research | | 09:21–10:33 | The challenge of ultra-short research dives at depth | | 11:24–14:25 | Introduction of ARMS (autonomous reef monitoring structures) | | 16:45–19:01 | Retrieval of ARMS in Palau, passing from diver to diver | | 19:01–24:56 | The “disassembly line” of identifying and processing ARMS samples in the lab | | 24:56–30:36 | Sorting species—triumph and limits of taxonomy, finding likely new species | | 31:00–32:55 | Understanding species relationships and associations on ARMS | | 33:25–33:47 | Motivation for deep reef research: contributing to a multi-generational scientific puzzle | | 36:39–37:29 | The episode wraps with a sea slug dance song and camaraderie |

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Episode Tone and Takeaways

The tone is curious, collaborative, and occasionally playful, with striking moments of awe and humility at the scale of oceanic unknowns. The episode demystifies how incremental, painstaking biological research works at the frontiers of science, emphasizing the value of teamwork and the power of sharing new puzzle pieces with future generations.

"No, we will not assemble the puzzle, no. But we'll generate some good pieces for the next generation to assemble." – Luis Rocha (33:39)

The mystery—and allure—of the twilight reefs lies in both the new species yet to be cataloged and, perhaps more importantly, in understanding how these pieces fit together in the deep, interconnected puzzle of life on Earth’s final frontiers.

Transcript

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[Fred Pinkerton]

Okay.

[Johanna Loiker]

Yeah.

[Fred Pinkerton]

Ok. Ready?

[Daniel Eisenhower]

Yeah.

[Emily Rudkowski]

Objectives, proficiency, and get some arms.

[Fred Pinkerton]

On a bright, 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. 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.

[Emily Rudkowski]

Team assignments deep, less deep.

[Fred Pinkerton]

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. Are all divers mentally and physically prepared for this dive? Absolutely. 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 debriefs for short. But they're a world that one of the divers, 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 they fundamentally do not understand.

[Emily Rudkowski]

Let the games begin.

[Fred Pinkerton]

So this is unexplainable. I'm Fred Pinkerton, and today on the show, how do you solve a puzzle like the deep reef? Luis Rocha started exploring the ocean early.

[Luis Rocha]

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 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 always very excited about discovering new things.

[Fred Pinkerton]

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. First, we will go somewhere with deep reefs, let's say Palau for now. And then we'll dive 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. And as we go deeper down to 40 meters and 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

[Sponsor/Advertisement Voice]

light

[Luis Rocha]

in 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 scientists, and it's riskier even from the human perspective. It's risky for the divers.

[Fred Pinkerton]

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.

[Luis Rocha]

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 that 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 at that level, those ecosystems are unknown.

[Fred Pinkerton]

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.

[Luis Rocha]

Now we probably have like 8 to 9 million pieces. And of those, I would say 5 million are assembled.

[Fred Pinkerton]

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

[Luis Rocha]

pieces to look at, so it's a lot less information to go with. There's so many big questions that need to be answered.

[Fred Pinkerton]

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.

[Luis Rocha]

But also, 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.

[Fred Pinkerton]

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 a 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 carbonated. Nitrogenated, really. So if you want to descend to 100 meters to explore the deep reefs, you get gassy very fast.

[Luis Rocha]

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

[Fred Pinkerton]

What can you do in five minutes?

[Luis Rocha]

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.

[Fred Pinkerton]

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 expanding, 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.

[Luis Rocha]

I tried playing Angry Birds in it. It was very, very. It made me very angry because I could never get. The touch screen 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.

[Fred Pinkerton]

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

[Luis Rocha]

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,

[Fred Pinkerton]

arms or arms for short.

[Luis Rocha]

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.

[Fred Pinkerton]

Arms were developed basically to study underwater ecosystems in A standardized way. So if you pick up an encrusted rock from a reef and 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, 3, 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.

[Luis Rocha]

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 accident, by anything you can imagine in the ocean. And it becomes this stable, diverse 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.

[Fred Pinkerton]

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 debriefs 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 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. 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.

[Luis Rocha]

All clear in the back.

[Johanna Loiker]

Clear.

[Fred Pinkerton]

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,

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[Fred Pinkerton]

Just crossed over into the Twilight Zone.

[Emily Rudkowski]

I think one of them is coming.

[Fred Pinkerton]

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. They're a boat length away. The shallower divers would emerge and they would pass a small clear tub to the people waiting on the boat.

[Daniel Eisenhower]

Got it?

[Fred Pinkerton]

Yes.

[Sponsor/Advertisement Voice]

All right.

[Fred Pinkerton]

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

[Johanna Loiker]

Looks like a goodie.

[Fred Pinkerton]

Some arms were a little sparser. Others were almost fuzzy with organisms.

[Emily Rudkowski]

Lots of sponges on this one, Emily.

[Fred Pinkerton]

But each one was quickly transferred from the small tub into a big black storage bin full of seawater. 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 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 picric, which is an institution devoted to coral research that was letting new scientists use their facilities for this work. 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 Cheez. It fueled sort of beautiful disassembly line.

[Emily Rudkowski]

Do you have another size wrench?

[Fred Pinkerton]

Step one was just breaking down the arms. Two researchers from Cal Academy named Johanna and Lynn were often helping with this part. 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. Which one? Okay, let me. I'm on sort of one thick square plate at a time. I think I got it.

[Emily Rudkowski]

Hold on.

[Fred Pinkerton]

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 splotches and streaks and swirls of red and orange and yellow and green. And they would place each other 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. And haul it over to a cool air conditioned lab nearby, before then returning to the bin that they had disassembled the arms in. And now back to the sounds of sloshing wood. 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.

[Emily Rudkowski]

Crab. Some shrimp. Shrimp, Shrimp, Shrimp, Shrimp.

[Fred Pinkerton]

Jumbo shrimp. 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 they began with the big picture, literally.

[Johanna Loiker]

So we are going to start plate photographing.

[Fred Pinkerton]

Chris, a Smithsonian curator who directs the global arms program, was the guy in charge of this big picture photography.

[Johanna Loiker]

Oh, you know what? This is kind of an important part. This piece here needs to be plugged into this computer. Forget to do that. Not much happens.

[Fred Pinkerton]

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

[Johanna Loiker]

So this is the photo mosaic fun part. It's kind of like nature's art.

[Fred Pinkerton]

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

[Johanna Loiker]

Are you guys ready?

[Fred Pinkerton]

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

[Emily Rudkowski]

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.

[Fred Pinkerton]

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.

[Emily Rudkowski]

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

[Fred Pinkerton]

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 tuna. So things like sea squirts, which he told me are actually our closest invertebrate

[Daniel Eisenhower]

relatives, they 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.

[Fred Pinkerton]

Across the table from both of them, Emily from the University of Hawaii was sampling sponges. Guys, this sponge is so cool. It's kind of poking and prodding them, cutting them up.

[Emily Rudkowski]

Sometimes when you cut them, they'll have, like.

[Fred Pinkerton]

There's this one that has, like, a

[Emily Rudkowski]

strong garlic smell when you cut it.

[Fred Pinkerton]

So you gotta make sure to smell them as well.

[Emily Rudkowski]

Yes.

[Fred Pinkerton]

You gotta ask them what they do on the weekends.

[Emily Rudkowski]

You know, it matters.

[Fred Pinkerton]

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. You know, I do.

[Emily Rudkowski]

I convert one person, and then they convert one person. It's like a triangle, you know, a pyramid scheme.

[Fred Pinkerton]

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.

[Daniel Eisenhower]

Well, we already did, right? Yeah.

[Emily Rudkowski]

It's on the edge.

[Daniel Eisenhower]

It's a sponge.

[Luis Rocha]

No.

[Fred Pinkerton]

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

[Emily Rudkowski]

It's firm.

[Johanna Loiker]

Yeah.

[Fred Pinkerton]

It's not as functional, like if something was a sponge or a tunicate or what.

[Daniel Eisenhower]

So it may be a tunicate, but it's really small. We couldn't see the. The siphons. So that's why I wouldn't call tunicate right away.

[Fred Pinkerton]

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.

[Sponsor/Advertisement Voice]

The family is Paguripseutidae, which literally means fake hermit crab.

[Fred Pinkerton]

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

[Emily Rudkowski]

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

[Fred Pinkerton]

Really, though, everyone in the lab was contributing to this sort of overall project of trying to figure out what was what it was this constant course.

[Emily Rudkowski]

Wow, he's cool. What is that?

[Daniel Eisenhower]

Who builds that?

[Fred Pinkerton]

Oh, that's an ostracod.

[Johanna Loiker]

I think it's an amphipod.

[Emily Rudkowski]

Could you write down 1570 is Caprelidae.

[Luis Rocha]

Oh, it's not a bimself.

[Johanna Loiker]

It's not a decapod.

[Emily Rudkowski]

I think it's a polynoid.

[Fred Pinkerton]

I think this is the hard text.

[Johanna Loiker]

This one's labraliniata.

[Fred Pinkerton]

Sometimes they could identify things with specificity.

[Emily Rudkowski]

Oscarella. Oscarella, for sure.

[Fred Pinkerton]

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. Then many, many others were more broadly identified by family or sub family or higher taxonomic levels.

[Emily Rudkowski]

Take a look.

[Fred Pinkerton]

And that's why they were trying to grab samples 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.

[Johanna Loiker]

Did you guys get this brachiopod looking this greeny sponge up here? See the brach right in the middle?

[Emily Rudkowski]

No, I don't have that at all.

[Johanna Loiker]

You grab it.

[Emily Rudkowski]

Okay, let me get a Tweezer, Grab some tweezers.

[Johanna Loiker]

I haven't seen that one.

[Fred Pinkerton]

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 at 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.

[Sponsor/Advertisement Voice]

It's your lucky.

[Johanna Loiker]

What have you got?

[Emily Rudkowski]

A third Nuda branch. Johanna found it.

[Johanna Loiker]

How exciting.

[Fred Pinkerton]

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

[Daniel Eisenhower]

Very cool.

[Fred Pinkerton]

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

[Johanna Loiker]

I think it's a. A discodorate of some sort.

[Emily Rudkowski]

Okay.

[Fred Pinkerton]

But he waited a bit for 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 nudibranch. He basically just started scrolling through like an incredible number of multicolored slugs. This very loud machine started running in the background and as Terry was scrolling, but eventually he landed on one slug in particular.

[Johanna Loiker]

Okay, so it's similar to that and it has that sort of network 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.

[Fred Pinkerton]

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, you seem very blase about a new species.

[Johanna Loiker]

I'm not blase, I'm excited. It's just, you know, another day's work. But I still.

[Emily Rudkowski]

Sir, do you want this here?

[Sponsor/Advertisement Voice]

What?

[Fred Pinkerton]

This is for you here.

[Johanna Loiker]

What is that?

[Emily Rudkowski]

The limpet, I believe, that Christian just sent over.

[Fred Pinkerton]

Do you want it here? 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, 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.

[Johanna Loiker]

Oh, Tito, is this our Medusa guy?

[Fred Pinkerton]

Chris and Tito, for example, were interested in a tunicate 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 pompom crab. He's so cute. Which turned out to be a tiny yellow crab holding purple anemones in its claws. Red to defend himself. Sarah, meanwhile, seemed especially excited about creatures that mimicked other creatures. So one night at 1:12am she showed me what she called the frosting on the cake of the day.

[Emily Rudkowski]

So these are ovulids.

[Fred Pinkerton]

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.

[Emily Rudkowski]

And the mimicry is so precise that that isn't a polyp on a coral. It's a papilla on the snail.

[Johanna Loiker]

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

[Fred Pinkerton]

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. 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 and this was a project to bring up more. And she said to me, oh, yeah,

[Emily Rudkowski]

so to be fair, you know, we have collections in museums, for instance, for exploring expeditions, and people would dredge and pull up weird, you know, meso to deep things.

[Fred Pinkerton]

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.

[Emily Rudkowski]

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

[Fred Pinkerton]

way, which is why you were so excited at 2:00am when you.

[Emily Rudkowski]

I was so excited at 2.

[Fred Pinkerton]

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 debriefs 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.

[Luis Rocha]

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

[Fred Pinkerton]

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

[Johanna Loiker]

No.

[Luis Rocha]

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

[Fred Pinkerton]

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

[Luis Rocha]

No, no.

[Fred Pinkerton]

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 Loiker. Obviously, I am aware that science is a process that involves a of lot, 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 Rudkowski. So I expected for this story to focus mostly on Luis, maybe one other researcher in the lab. I'm Sarah Tweed. 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 Piotrowski.

[Johanna Loiker]

My name is Terry Goslinger.

[Luis Rocha]

My name is Matt Schmidt.

[Fred Pinkerton]

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

[Luis Rocha]

So my name is Luis Rocha from here in Palau.

[Fred Pinkerton]

Some of the samples collected will go back to the California Academy of Sciences. Others will go to the Smithsonian. It's Chris Meyer, the University of Sao Paulo and elsewhere, who name is Tito

[Daniel Eisenhower]

Monteiro da Cruz Lotufo, short version, Tito Lotufo.

[Fred Pinkerton]

Last year, they brought up the arms that they'd left in Guam. I'm Daniel Eisenhower, and the University of Guam kept many of those samples in their collections. 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.

[Emily Rudkowski]

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

[Fred Pinkerton]

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. So, sure, yes, Louise 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.

[Emily Rudkowski]

This sponge.

[Daniel Eisenhower]

Oh, this is. You.

[Emily Rudkowski]

To brain songs.

[Sponsor/Advertisement Voice]

Much better.

[Emily Rudkowski]

What is this? What's a Nudibranch song?

[Fred Pinkerton]

Sorry. Yara has pulled up a video that's called Psychedelic Sea slug dance on YouTube.

[Daniel Eisenhower]

Wait until you listen to this.

[Emily Rudkowski]

You don't need to see, okay? Just listen.

[Daniel Eisenhower]

The nudie brand started way long ago in the ocean deep below it was the latest craze in town it was the greatest dance around the newly branched branch the psychedelic sea slug dance Dance to the nudie, nudie, nudie branch it's the latest, it's the greatest Come on, baby, do the new deep branch dance

[Fred Pinkerton]

this episode was produced by Me, Bird Pinkerton. It was edited by the wonderful Lissa Sew up and by Jorge. Just thanks Jorge and Lissa for everything. Joanna Solotaroff and Meredith Hodnot 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, Miles Uwell, Chris Shurtleff and Davon Howard helped me with gear. Valerie Shenkman, Alex Coles, Kareem Correa, and Sally Helm are. The fact that some corals can fly.

[Sponsor/Advertisement Voice]

Fluoresce.

[Fred Pinkerton]

Thanks always to Brian Resnik 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 were working on this Palau project who walked me through what they were up to. But an especially big thanks to Johanna Loaker for taking so much time, both before 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@ unexplainableox.com 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 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.

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[Emily Rudkowski]

Close your eyes, exhale, feel your body relax and let go of whatever you're carrying today.

[Fred Pinkerton]

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[Fred Pinkerton]

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