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The nautilus inhabited the deep waters surrounding forest-clad Manus Island, an exclamation point at the northwestern end of Papua New Guinea’s Bismarck Archipelago.

It lived slowly and in near-complete darkness—its large eyes tuned to the blue wavelengths of bioluminescent bacteria that signaled a carcass to scavenge, and just sensitive enough to tell night from day 300 meters below the surface. Its 90 tentacles and superlative sense of smell aided its search for food along the seafloor. And as it grew, it added new chambers to its spiraling shell.

When the nautilus died—at perhaps 20 or 30 years old—its soft, squid-like body rotted away. Its shell lost the neutral buoyancy that allowed it to cruise effortlessly at whatever depth it chose, and it floated to the surface. Currents washed it into the mangroves, or onto one of Manus’s palm-fringed beaches, or perhaps onto a nearby coral-ringed atoll, called Ndrova Island.

Wherever it landed, the shell’s elegant cream whorl with rust-brown stripes would have caught the woman’s eye as she gleaned for shellfish. She took it home with her, made it useful.

Manuai Matawai grew up watching his mother, like the other women in his fishing village, use the nautilus shell’s sealed outer chamber as a scoop for separating fragrant coconut oil from the fruit’s starch at the bottom of her cooking pot. The nautilus—called kalopeu in the local Titan language—was also the symbol of a prophet Matawai followed. But like most in his coastal community, he had never seen one alive, because of its preference for the cold, dark depths.

Then, in 2015, he had his chance. Researchers from Australia and the United States came to study the creature, and Matawai, then working for the Nature Conservancy (TNC), helped organize their expedition to Ndrova. Peter Ward, a paleobiologist at the University of Washington widely known as “Professor Nautilus,” had last visited in 1984, when he and a collaborator were among the first people to examine a live fuzzy nautilus, a species belonging to a new genus that they later named Allonautilus scrobiculatus. Ward and his colleagues had come back to see if the fuzzy nautilus and the better-known chambered nautilus (Nautilus pompilius) were still there, and to try out some new research tools.

From left, Pomat Kanawi, Gregory Barord, Peter Ward, and Manuai Matawai snorkel off Ndrova Island, Papua New Guinea, in search of the little-understood and rarely seen nautiluses. Photo by Manuai Matawai

Only a handful of scientists study nautiluses, and many of the most basic questions about the creatures’ lives haven’t been resolved. And yet, they have captivated humans for centuries, their shape inspiring art, architecture, and math across many cultures. The underwater ship in 20,000 Leagues Under the Sea was called Nautilus, as was the first nuclear submarine. Today, numerous companies, from wineries to exercise-machine manufacturers, also employ the name.

“I don’t know if it’s the most mysterious well-known animal or the most well-known mysterious animal,” says Gregory Barord, who joined the 2015 expedition led by Ward. The scientists hoped to dispel some of that mystery through their research in Ndrova—but what they found sparked yet more questions.

Soon after Ward hauled on his dive gear and descended the steep reef walls, he noticed the change. In 1984, the scientists had been harried by sharks. “They were nasty, cranky little bastards, so I was kind of dreading going through that again,” Ward recalls. But this time, they didn’t see a single one, suggesting a change in the ecosystem. There was also evidence of coral bleaching, and waters that had been pleasantly cool below the shallows now felt uncomfortably warm.

The experience inspired Ward to pursue a new line of inquiry, analyzing the composition of nautilus shells to track climbing temperatures in the deep sea, and looking to nautilus behavior to predict how these changes might affect his beloved study subjects.

Climate change is dramatically altering life in the ocean all over the world, and extreme heat is now normal in many places. Ward believes nautiluses may already be seeking refuge in cooler, deeper waters to cope. But there is only so far the mollusks will be able to swim. Below 800 meters, the pressure is enough to make their shells implode.

A shop in the Philippines sells piles of spiraled nautilus shells from a large bin. More than 100,000 nautilus shells were imported into the United States alone between 2005 and 2014. Photo by Greg Barord

At the same time, human desire for the animals’ beautiful mother-of-pearl shell has led to overfishing in some parts of their tropical Pacific home. “It’s the nautilus’s bad luck that it’s got this beautiful symmetry,” says Ward. Their shells can go for US $1,000 on eBay. Between 2005 and 2014, trade data collected by the US Fish and Wildlife Service indicated that more than 100,000 whole nautilus shells and 800,000 parts were imported into the United States alone. Some once-abundant populations in the Philippines—where nautiluses are also occasionally hunted for food—may already be extinct.

As climate change looms, so does a single question among all those that remain about nautiluses: can they survive us?

Nautiluses have certainly always been survivors. Ancient and cunning, their lineage was adaptable enough to persist through all five of Earth’s major past extinction events. Their ancestors, the nautiloids, appeared half a billion years ago. They were the first cephalopods, a group of mollusks that today includes octopuses, cuttlefish, and squid.

Back then, most life crawled along the seafloor, but the nautiloids were able to float suspended in the water—a key innovation they achieved by removing liquid from their innermost chambers to match the density of the seawater around them, rendering them essentially weightless. The earliest nautiloids had straight, conical shells, but they soon evolved the coiled spiral with interconnected internal chambers seen in nautiluses today. In their current incarnation, they’ve cruised the oceans for at least 100 million years.

It was in this shape that they weathered the asteroid that ended the age of the dinosaurs. Debris from the impact and ash from the fires that raged afterward obscured the sun for two years, killing most of the photosynthesizing plankton that formed the basis of the food web in the shallows. Nautilus species that lived near the surface likely starved into extinction along with their relatives, the ammonites.

The same but different: a chambered nautilus floats next to a fuzzy nautilus, with its slimy outer layer. Photo by Peter Ward

But in the perpetual twilight known as the Mesopelagic Zone, between 200 and 1,000 meters below the surface, other nautilus species persisted. And because today’s nautiluses are thought to be mainly scavengers, the mass death and destruction may even have benefitted them, suggests Ward. After all, he says, “What was left after the Cretaceous was over? Dead bodies.”

A more personal tragedy kept Ward from nautilus field research for several decades. On an expedition to New Caledonia in late 1984, his dive buddy drowned while the pair checked on nautilus traps. The 2015 expedition was his first foray back to Papua New Guinea.

The team, which included Barord and TNC’s Richard Hamilton, traveled to Ndrova aboard a 14-meter, two-masted outrigger canoe that Matawai had built for a climate change awareness voyage a few years earlier. The island is a particularly good spot for nautilus research: the seafloor drops away so sharply from its shores that a trap laid on the bottom hundreds of meters below the surface can simply be tied off to a coconut tree.

Ndrova’s chief, Peter Kanawi, welcomed the researchers, and 18 community members joined the expedition as assistants. Every evening, as the tropical sun sank into the sea, the team set out in small motorboats and lowered the traps—cubic metal frames covered with chicken wire and baited with tuna. At dawn, they’d haul the ropes up by hand—a grueling workout that took nearly an hour per trap—stopping when the cage was within snorkeling distance of the surface.

Researchers studying nautiluses off Papua New Guinea trap the shelled animals to weigh, measure, sex, and take samples before returning them to the water. Video by Dave Abbott

The first night, the traps caught nothing. Some locals speculated that the foreigners hadn’t been properly introduced to the ancestors. But an elder fisherman who had been on the earlier expedition recalled that the traps had been set in a different spot in 1984, at a slightly shallower depth. On their next outing, the team did as he suggested. In the morning, Hamilton dove overboard to check the trap.

A coral reef biologist used to studying the shallows, he looked forward to this daily reveal. “You feel like a little kid doing a lucky dip. It was all stuff I hadn’t seen before—sort of a visual appreciation of just how much you don’t know.” Sometimes there were strange eels, and Hamilton particularly liked the “weird-looking crabs.” But that day, he was thrilled to count three fuzzy nautiluses and three chambered nautiluses.

Nautiluses are accustomed to the deep and can’t survive long in the warm surface waters of tropical seas. So once back aboard the outrigger, the scientists placed the animals in a seawater-filled cooler, chilled with frozen water bottles.

It was obvious which were the fuzzy nautiluses. Their shells were covered in a gooey, hairy periostracum, or outer layer, that’s completely absent in other types of nautilus. “It kind of feels like wet slimy fur,” says Barord. Ward originally believed that the slime made it harder for predators to get a grip on the creature’s shell. But he now thinks it protects against breaks.

If a triggerfish bites a chambered nautilus and snaps off the outermost edge of its shell, the animal will lose its carefully calibrated neutral buoyancy—imagine a diver’s weight belt falling off—and rise from the cool, comfortable depths. “You go to the surface, you’re dead. The temperature will get you if the seabirds don’t get you first,” says Ward. If the same thing happens to a fuzzy nautilus, that crucial bit of shell won’t fall away; the fuzz holds it in place.

Ward and Barord carefully weighed and measured each nautilus. They also sexed them, which involved turning the shell upside down until the animal emerged slightly, revealing the genitals. “It’s a boy!” Ward crowed.

Biologist Gregory Barord tips a nautilus upside down to coax the animal out of the shell so he can determine its sex. Photo by Dave Abbott

In the old days, researchers killed the nautiluses they caught, using whole shells for their work; Ward’s office is full of the spoils of his expeditions. By 2015, he regretted each death and had vowed not to kill anymore. Instead, he broke off a sand grain–sized fragment of shell and clipped off a millimeter of tentacle for chemical and genetic analysis back in the lab.

Next, the scientists attached battery-powered transmitters to three of the creatures in their cooler. Since the 1980s, the devices had gotten much smaller—around the size of a AA battery—but they needed to be set into a low-density fiberglass saddle to ensure they did not affect the animal’s buoyancy. Matawai and Ward stuck the saddles to the nautiluses’ shells with epoxy resin and held them half-underwater while the glue dried.

Then, the researchers put on scuba gear and jumped over the side, upending each animal to release air pockets—“we burp ’em, we call it,” says Ward—before swimming them down about 30 meters and dropping them into the deep. Matawai felt moved as he watched the beloved shells swim off into the gloom. “For someone who depends on the ocean for survival,” he says, “it was amazing to see what happens down there.”

Nautiluses affixed with radio transmitters await their release into the wild. Photo by Peter Ward

For the next six days and five nights, the team worked shifts, tracking the transmitter-wearing nautiluses in small aluminum fishing boats, without cover from glaring sun, soaking squalls, or evening winds, to find out more about their behavior and habitat.

As the nautiluses went about their business on the seafloor between Ndrova and Manus, their transmitters sent sound waves up to the researchers’ receivers, recording each animal’s depth, its location, and the surrounding water temperature. Since the two species coexist here, the experiment was also a chance to investigate differences in their behavior.

All three tagged nautiluses rose to shallower water—around 100 meters—during the night. But during the day, the two tagged fuzzy nautiluses dove to around 200 meters, near the steep reef wall, while the chambered nautilus went out to the muddy plains at 300 meters, and even swam in midwater all the way across to the Manus mainland. Previously, scientists had assumed they stuck to the seafloor and rarely traveled long distances. This newly revealed migration may bode well for nautiluses’ resilience against overfishing, Ward thinks, by allowing them to repopulate areas that have been cleaned out.

But in a warming sea, they may simply have fewer places to go. On land, climate change is already affecting the people of Manus Island, Matawai says. In December, king tides flooded some of the low-lying islands, drowning banana orchards and food gardens in lethal salt water. Underwater trends are less obvious, but globally, the signs are ominous. More than 90 percent of the warming that has happened on Earth during the past 50 years has occurred in the oceans. Average sea surface temperatures have risen consistently since the 1950s, and below 300 meters, the water is warming even faster.

Off the coast of Ndrova Island, a chambered nautilus stretches its tentacles while a fuzzy nautilus swimming nearby shows off its hairy, slimy outer layer. Photo by Dave Abbott

In one recent study, researchers predicted that by the second half of the 21st century, “a rapid acceleration” of heating will occur throughout the water column, forcing animal populations to move into deeper water or closer to the poles to survive. They found that change is likely to happen fastest in the mesopelagic zone, 200 to 1,000 meters below the surface, where nautiluses make their home—and below which they cannot retreat. But even if the world’s governments take immediate meaningful action to cut greenhouse gas emissions, significant warming at these depths is probably already baked in.

And it’s not just about overheating. Because different parts of the ocean are warming at different speeds, the changes are likely to also disrupt food webs and rearrange ecosystems. So far, though, around Manus, the nautiluses seem to be adapting. Back in the lab in Seattle, Washington, Ward analyzed his collection of Ndrova nautilus shells—some from 1984, the shell fragments from 2015, and a whole fuzzy nautilus shell he bought in a curio shop in Adelaide, Australia. The owner there said he’d picked it up on Ndrova in 1975. It cost AUD $200—steep, Ward thought, but scientifically worthwhile.

With a whole shell, you can take a chunk of each septum—the thin partition between the internal chambers—and the oxygen isotopes trapped within provide a record of the average sea temperature over the month or so the chamber took to form. “So a shell is a 20- or 25-year record of temperature,” Ward says—almost like tree rings. The tiny samples taken from 13 living animals’ shells in 2015, meanwhile, each provide a single data point—a snapshot of the sea temperature when their last chamber grew.

Ndrova Island chief Peter Kanawi palms two species of nautilus found off the coast of his island home. Photo by Peter Ward

The results show the 1975 animal inhabited waters averaging between 12 and 14 °C, while those from 1984 and 2015 lived in temperatures of around 16 °C. Ward was surprised the shells offered no evidence of warming water over those three decades, but says it’s possible the nautiluses simply moved deeper to stay cool. Since the transmitters the team attached to the animals in 2015 record water temperature and depth, in future versions of the experiment the living nautiluses may reveal with more certainty how their home might be changing.

The deepest part of the strait between Ndrova and Manus is only around 400 meters deep. If the warming continues without reprieve, says Ward, eventually the nautiluses must move somewhere new or perish. And while nautiluses have famously survived many periods of dramatic change, few have been as rapid as the one happening now. Even the so-called Great Dying that marked the boundary between the Permian and Triassic periods 250 million years ago took tens of thousands of years to unfold, says Jennifer Basil, a nautilus expert and behavioral ecologist at the City University of New York. “We’re worse than the Permian extinction.”

What would be lost, if we lost the nautilus? Not just beauty, but brains, too. In the past, some marine biologists have dismissed nautiluses as “dumb snails,” the least intelligent of the cephalopods. The suggestion greatly offends Basil, who has studied chambered nautiluses in her Brooklyn, New York, lab for more than 25 years. Her hair is a color her students call “nautilus auburn,” and she has nothing but enthusiasm for her subjects. She and her doctoral students call them “the kids,” and Basil says looking after them is like parenting a gang of troublesome 12-year-olds: “‘I’m gonna go out the outlet pipe. I’m gonna fight for some shrimp even though I have some.’ They’re always trying to injure themselves.”

Basil studies animal brains and behavior—hamsters, jays, chickadees, lobsters—but she finds nautiluses particularly compelling because they can help answer questions about the evolution of intelligence. As a group, cephalopods have the most gray matter of any invertebrate on Earth, Basil says—“big, fat, sassy brains” that evolved hundreds of millions of years before the vertebrate brain. But while octopuses, cuttlefish, and squid live fast and die young after laying a thousand eggs, nautiluses don’t mate until they are at least 10 years old, then lay a handful of eggs that take a year to hatch. “They are solving problems in a different way with a different brain.”

Basil’s early studies showed that nautiluses have superior powers of smell—they are able to detect very low concentrations of odors at distances of more than 10 meters, and move toward the source with great accuracy by comparing minute differences in the intensity of the odor reaching the receptors on each side of their body. In other words, they smell in stereo—an adaptation requiring complex sensory processing, and a surprise in such an ancient animal.

A nautilus wobbles through the water. Studies in captivity have shown that nautiluses move through their environments aided by superior senses of smell. Video by Dave Abbott

Their eyesight isn’t bad either. In another experiment, Basil and doctoral student Robyn Crook strapped each nautilus into a harness—dubbed the “nautilus car seat”—and exposed them to a flash of blue light, giving the animals some food immediately afterward. Just like Pavlov’s dog, the nautiluses learned to respond and continued to do so hours later, proving they have both short-term and long-term memory.

Reflecting on how well nautiluses hide their eggs—no one has ever seen them in the wild—Basil and Crook tested their spatial memory by putting them in a maze in a tank with uncomfortably shallow water. The nautiluses quickly found their way to a hole that led to deeper water by learning its association with a beacon made of bubble wrap and white tape. When Basil arranged some different objects pointing toward the hole instead, the nautiluses mastered that cue, too, even after the researchers put the beacon back elsewhere. Finally, they turned the entire maze 180 degrees, so that Basil’s beloved wall poster of 20th century chemist Rosalind Franklin shifted relative to the hole. This time, the nautiluses went to the wrong place—the place the room told them to look, rather than the beacon. It was 2:00 a.m. and Basil and Crook glanced at each other, stunned, as if to ask, “Did that just happen?”

The nautiluses’ confusion demonstrated their intellect. Rather than using simple, local cues, they were looking outside of their tank to consider global cues. In nature, those are much more reliable. “That’s what’s so great about working with these guys. They always surprise you. They’re always more capable than you thought,” says Basil. “And they have illuminated the history of big brains in a way that wouldn’t have been possible with any other lineage.”

Although Barord and Ward have spent more time with nautiluses in their natural habitat, Basil perhaps knows them more intimately. Number 3 was the teacher’s pet. Number 13 was always trying to break out of her car seat. Number 9 lived the longest in captivity, 10 years, and he was Basil’s favorite: “Oh, he was a prince.” He would curl his tentacles around her finger when she reached into the water, and when he got old, Basil gave him a “retirement tank” and his favorite food—lobster carapaces she scrounged from fancy New York restaurants.

Basil was “broken up” after he died (she still has his shell). The inevitable emotional attachment is the joy of studying these remarkable creatures, she says—and the steep price of facing their possible disappearance.

In September 2016, Barord sat amid a crowd of international delegates and representatives of NGOs in a conference center in Johannesburg, South Africa. Hidden under his formal shirt was a new tattoo, a gift to himself on receiving his doctorate—a life-sized nautilus, wearing a tracking transmitter, swimming along his upper arm. He, Ward, Basil, and other nautilus researchers had put in years of work alongside officials from the governments of Fiji, India, Palau, and the United States to get the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) to require permits for commercial export of any nautiluses.

In theory, such regulation would reduce fishing pressure by limiting international trade. Finally, it was coming to fruition. Barord felt proud and exhilarated as he listened to the chair make the announcement adding the nautilus to the list. But the feeling quickly gave way to dismay as the crowd applauded one species after another joining the litany of animals in trouble—the silky shark, thresher sharks, all nine species of devil ray.

It was a grim chronicle, Barord says, of “how poorly we have managed our resources on this planet and how thoughtlessly we have cared for other species.” Barord remembered that Baja California’s vaquita porpoise had been added to the CITES list back in 1976. That hadn’t stopped its population from dropping to single digits. For nautiluses, he realized, CITES was just the start. Today, despite the changes, nautilus shells can still be easily bought online.

In 2019, though, Barord made another nautilus voyage that lifted his spirits.

This time, he and Hamilton traveled to Marovo Lagoon, a dazzling archipelago of palm-studded, coralline islets in the Western Province of the Solomon Islands, a Pacific nation to the east of Papua New Guinea. No scientist had found fuzzy nautiluses alive there before, but their shells had long washed up on beaches, and Hamilton had seen some displayed in a bar in nearby Isabel Province.

A fuzzy nautilus bobbing in the deep sports a radio transmitter that will allow researchers to track its movements and learn how it behaves beneath the waves. Photo by Peter Ward

Every evening, alongside the chicken-wire fish traps, they dropped a lighted camera trap called a Baited Remote Underwater Video Station (BRUV) in hopes of collecting the first-ever film of a fuzzy nautilus in its habitat.

Soon, they had caught both fuzzy nautiluses and chambered nautiluses in the live traps. The team had proved that both species live in the Solomons, and had found only the second place after Ndrova where the two types are known to coexist.

Ashore on a nearby island, Barord sat under the coconut palms and loaded the footage from the video traps onto a small camcorder. What he saw mesmerized him: a fuzzy nautilus and a chambered nautilus were swimming around together, both attracted by the bait. The fuzzy nautilus not only looked scruffier than the chambered one, it moved slower. Researchers had noticed this difference between the two species before, but for Barord, seeing them together in real time was a revelation.

“It was acting differently in its environment,” Barord says. “It just kind of connected for me how these animals have been able to survive for this long. These tiny little behavioral changes … it’s not a huge thing that they’re changing. They’re just tweaking, calibrating a little bit.” Smooth shell, fuzzy shell. Shallower, deeper. Faster, slower.

“It’s hard for me to envision 500 million years, but these little changes in these two different genera just put it all into perspective for me of how they’ve been able to adapt in a very different way than other animals have.” The moment filled Barord with hope for the nautilus’s resilience—that despite the mounting threats, these mysterious creatures will find a way to survive.

Matawai shares that hope. Hanging on the wall of his home on Manus Island is a banner emblazoned with the distinctive coil of a nautilus shell. It is the flag of the Win Nation, Matawai explains, a syncretic spiritual group consisting of followers of the late prophet Sir Paliau Moloat, who some consider a “Melanesian Jesus.”

The nautilus’s shell symbolizes a vessel, Matawai says. The soft body of the animal inside represents the people of the Win Nation. Protected by the shell, they sail forth into eternity, guided by the stars. It makes sense, as an emblem: a mysterious creature that has existed in various forms for half a billion years is about as close to immortality as life on Earth gets. Perhaps nautiluses will soon be gone. Or perhaps, against all odds, they will be around for half a billion more.