An Audacious Plan in the Twilight
The moment they fall backward through the turbulent surface, the three divers turn to look straight down—but all they see is the blue-black haze of depth. Despite the ominous view, they immediately relax their arms and legs and allow themselves to free-fall, heavier than saltwater, into the unknown below.
Careful to stick together, they glance at one another every few seconds as they drop. They look for signs of physical or psychological distress, and for equipment problems, such as bubbles escaping from the sealed “rebreathers” strapped to their backs—the equipment that will keep them alive underwater for the next five hours. The same equipment that could kill them if they fail to recognize a malfunction.
Despite the inherent risks, this is the moment they’ve been waiting for. What they’ll witness over the next 25 minutes is what it’s all about for these three. They are members of an elite, yet widely dispersed, group of scarcely a dozen scientific divers who dare to plunge into a strange, half-lit region between 200 and 500 feet below the ocean surface, a place called the “twilight zone.” It’s the chance to see things no one else on Earth has ever seen before, to discover new species, and to begin to understand what role these deep, cold, low-light, high-pressure habitats might play in the ecological health of coral reefs in general.


Bart Shepherd, 45, the expedition’s leader, spent many years and hundreds of dives teasing the edge of the twilight zone. “I did a lot of diving at the 120-foot range, and you could always look over that edge and see it kind of drops off… it’s this mystery,” he says. “I always wanted to go down there.”
But without the technology and training required to safely plunge to these depths and return to the surface, he wasn’t tempted enough to throw caution to the wind and actually go. With long, relaxed limbs and a laid-back conversational style that belie both his drive and his fastidious attention to detail, Shepherd lacks the bravado and risk-loving nature you might expect from a member of this exclusive group of deep-reef explorers. He’s not a natural risk-taker, he says. With a wife and two daughters back home—all of whom expect a daily FaceTime call when he’s away on expedition—he says he’s only willing to accept “manageable risks,” and only if the objective is worthwhile.
Which is why he and his two co-conspirators—Brazilian ichthyologist Luiz Rocha, 42, and Rocha’s tireless Ph.D. student Hudson Pinheiro, 35—now find themselves in the South Pacific, just off the coast of a tiny sliver of land known as Hat Island, accelerating past a depth of 150 feet en route to the twilight zone. They all know that both in terms of this dive and in the much larger picture of coral reef research and conservation, there’s no time to lose.

“Coral reefs as a concept were defined by the top 100 feet.”
— Richard Pyle
Controlled Chaos
For Shepherd, Rocha, and Pinheiro, today is Day 11 of a 13-day expedition, and the last of a string of multi-hour dive days off the coast of Vanuatu. The tension between the thrill of exploring the unknown and the extreme difficulty and risk inherent in diving a distance equivalent to the height of a 30-story building has been a continuous undercurrent throughout this expedition. When not on a boat or underwater, the team has spent almost every waking moment over the past two weeks reviewing dive footage, cleaning and prepping gear, reviewing safety procedures—and of course, poring over reef-fish identification guides, making comparisons between the shallow-water species those guides typically contain and the fish the divers have seen in the twilight.
Shortly, the team will drop one final time into the depths before packing up for home. With the expedition coming to a close, the pressure to deliver has peaked. After months of planning and tens of thousands of dollars spent, the cost-benefit analysis is tipped strongly in the wrong direction. And no one is feeling the intensity of the day more than Shepherd, who will be held responsible if the expedition is deemed an expensive flop.
As the sun climbs high overhead, everyone aboard the tiny boat is reminded that there’s no time to lose. Not that the reminder is particularly useful at this stage. The local boatman, Eroni, is willing the craft forward as quickly as possible. But with just a 30-horsepower engine churning the water behind, and decent-sized swells ahead, he can only push the patched and stressed fiberglass so hard—particularly here, just off the tip of Devil’s Point, a spot known to eat boats like this one.
Shepherd stares out across the dark water toward the ragged shoreline. Speaking to no one in particular and with a wry, exhausted smile spreading across his face, he shouts, “Where are we going again? Why are we doing this?”
Before long, the boat rounds the point and an island the shape of a crushed fedora angles into view: Hat Island. With their destination still 30 minutes away, the team seizes the opportunity to snatch a few more calories to sustain them during the five-plus hours they’ll soon spend underwater. They scrounge for what’s left of the snacks, which at this stage of the expedition amounts to four apples, a bag of salted peanuts, and a family-sized purple Mylar bag stuffed with Cheetoh-style snack puffs that no one seems desperate enough to open.
The dwindling supply of food is not the only sign that the expedition must soon draw to a close. Fatigue runs bone-deep, and the chatter that filled previous days’ boat rides across Vanuatu’s Mele Bay has faded into blank stares. This being a dive site they’ve been to before, the only site they will revisit all trip, they have some idea what to expect—as much as you can hope to know about a place 300 feet below the ocean surface, where light is cut in half, temperatures plummet, and currents come out of nowhere, like underwater squalls that push divers more often than not in directions they don’t want to go.
With the dive fast approaching, the team quickly abandons the hunt for snacks to focus on more urgent matters: the mental checklists, instrumentation, and procedures designed to keep them alive underwater.
The protocols for deep diving are significantly more complex than those for recreational diving. That’s partly because the equipment itself is more complex. But there’s another more daunting and viscerally compelling reason: deeper means farther from help. If anything goes wrong while Shepherd and his team are underwater, they’ll need to resolve that problem down there. There’s no such thing as an emergency ascent from 300 feet. Which of course means that the team needs to be equipped to deal with any and all underwater emergencies. And that requires a lot of gear.
The race to attach all that gear and get ready to roll into the water together begins the moment Shepherd, Rocha, and Pinheiro begin suiting up. This synchronized entry wouldn’t be necessary if the boat were anchored in calm seas, where the divers could drop in one at a time and wait at the surface. But in this narrow, deep, turbulent channel between Hat Island and the main island of Efate, cruising anchorless, or “live boating,” is the only option. And so the divers all have to stay onboard and endure the seemingly endless addition of thermal layers and equipment, each piece making them hotter and heavier.
Coordinating this controlled chaos and doing most of the heavy lifting is Will Love, the expedition’s dive-safety officer. Having organized the tanks and gear as neatly as possible in the bottom of the undersized boat, Love leaps from diver to diver, piling on one massive piece of equipment after another.


High-tech on island time



The world at 300 feet
Warnings against complacency are a standard refrain among scuba divers, but the message is particularly relevant at this moment, as the team begins its drop into the twilight. The first few minutes of a dive are perhaps the most critical of any. Not only is the early part of a dive when equipment problems caused in transit are more likely to show up, but it’s also the only time when a diver can call it off and resurface relatively quickly. Beyond this point, after just a few minutes at depth, resolving problems underwater is the only option.
At first, the only cues orienting the divers to their whereabouts are the direction of their free-fall and a gradient of color, from robin’s egg blue looking toward Hat Island to an ominous black near the center of the channel.
Then, as they near a depth of 200 feet, the divers spot a rocky ledge in the distance. It’s another 100 feet down a steep, sandy slope, but Rocha will recall seeing that ledge and the dropoff just beyond and thinking, “Shit, that’s nice. This is going to be epic.”
When they reach the slope, they turn and continue down toward the ledge, which sits near their planned max depth of 325 feet. Swimming along a sandy slope, even one as steep as this, is about the last thing they want to be doing at this early stage of a dive. Every horizontal foot they swim is stealing precious time away from the moments they’d rather spend in more interesting habitat farther down—time they’d rather spend catching fish, instead of working hard just to get there.
By the time they hit 300 feet, they’ve already spent a considerable amount of time at depth, but what they find when they arrive at the ledge doesn’t disappoint. As they adjust their buoyancy and look around, their beams cut through the half-light to reveal a coral reef that is utterly alien.

Gone are the forests and tabletops of branching corals and the immense brain coral orbs found in the light-bathed shallows. They’re replaced by a community of hardier species, more stunted but no less vibrant. Calcareous algaes and plating corals hug the bottom, painting the ancient limestone substrate in psychedelic hues. Delicate sea fans and wire corals stretch upward, appearing determined to maximize their surface area and make the most of what little light finds its way this far down.
Although the starfish and sea cucumbers here maintain the same general shape as their shallow-water cousins, they tend to be more heavily armored with spikes and knobs. Exactly what these animals are defending against is difficult to say, because no one knows much at all about any of the organisms that live here—or the ecosystem they’re a part of.
Then there are the fish. Like the daydream creations of a child left with nothing but the brightest crayons in the box, twilight zone fishes are some of the most beautiful things on the planet. In the full-spectrum light of the divers’ beams, they practically glow in hues of pink, red, orange, yellow, and blue.

Less than halfway home
“During the whole dive, you have to be thinking that the rebreather is trying to kill you. If you don’t take it that way, it will kill you.”
—Luiz Rocha
The three divers are now lugging those decompression chambers into a strong current as they head back up the sandy slope toward their first of many decompression stops, at 200 feet. Knowing that working hard at depth only causes the body to absorb more nitrogen, Shepherd later remembers thinking, “I should not be breathing this hard, this deep.” But there’s not much the divers can do about the conditions they’ve been dealt, and there’s only one way out. So they slog on.
At 200 feet, they pause to catch their breath and to seal the fish into the chambers. Although a stop at this depth should last only a minute, the team won’t take any chances with this precious cargo. It takes them a full five minutes to carefully place the collection jars in the chambers, seal them, and release oxygen boosters into the chambers before continuing their swim up the slope.
In general, the team’s decompression stops will grow progressively longer over the course of the dive. This is because the pressure difference between 15 feet and 30 feet is much greater than the difference between 215 and 230. That means it’s much more likely for dissolved gas to “boil out” of tissues and cause the bends when the divers reach the shallows than when they’re still fairly deep. So at their next stops at 165, 152, and 140 feet, they spend just one or two minutes.
When the team reaches 110 feet, it’s time to notify Love and the rest of the support team of their whereabouts. They send up a surface-marker buoy, an inflatable nylon tube that they fill with air from one of their tanks while holding on to a reel at the other end of the line. They’ll pull this bright orange kite along with them for the remainder of the dive. Just over an hour into the dive, this is the first indication to the surface team of their location—and that everything is okay. It’s now time for Love and the divers above to mobilize as quickly as possible for their underwater rendezvous.

The plan is to meet at 100 feet, and as Shepherd, Rocha, and Pinheiro make their way up to their next stop, they can see two boats motor over to the buoy above, and then four divers plunge in and start to fall toward them. This underwater meeting is the moment when aquarium biologists Margarita Upton and Nick Yim assume responsibility for the health and well-being of the fish for the next two days—at least until they’re loaded onto a plane en route to San Francisco. The delivery goes off without a hitch, and after just ten minutes, Upton and Yim begin their ascent.
Anxious to get the chambers up to the surface, the two biologists make their way to the boat as quickly as their obligatory safety stops will allow. Once there, they hand the chambers up and climb onboard. Time is critical. Every minute the chambers sit stagnant on the deck, the water inside is getting warmer and more contaminated with the fish’s own waste.
Beyond bragging rights

“I don’t need to know every species that lives there to know that an ecosystem is worth protecting.”
—Bart Shepherd
From Vanuatu’s Twilight Zone
Love what we do? You can help.
We’re a free and independent multimedia magazine without a paywall or intrusive ads—and we’d like to keep it that way. We believe these stories need to be told, that inspiring both a deep appreciation for life on Earth and hope for its future is a critical step toward a thriving planet. If you agree, please consider making a donation to help secure the future of bioGraphic. Every little bit helps.
Tom Yulsman

Steven Bedard is the co-founder and editor-in-chief of bioGraphic. Having spent the past 20+ years creating science content, he has written and produced immersive, multi-screen experiences, short- and long-form documentaries, interactive simulations, and hundreds of articles and essays on topics ranging from astrophysics and archaeology to genetics, evolution, and public health. As a former field biologist who spent the early 90s studying spotted owls and northern goshawks, he has found his happiest place covering the natural world for bioGraphic. Follow him on Twitter @steventbedard.