Below the Edge of Darkness

A Memoir of Exploring Light and Life in the Deep Sea

About the Book

A pioneering marine biologist takes us down into the deep ocean to understand bioluminescence—the language of light that helps life communicate in the darkness—and what it tells us about the future of life on Earth in this “thrilling blend of hard science and high adventure” (The New York Times Book Review). 

NAMED ONE OF THE BEST BOOKS OF THE YEAR BY BOOKLIST • “Edith Widder’s story is one of hardscrabble optimism, two-fisted exploration, and groundbreaking research. She’s done things I dream of doing.”—James Cameron

Edith Widder’s childhood dream of becoming a marine biologist was almost derailed in college, when complications from a surgery gone wrong caused temporary blindness. A new reality of shifting shadows drew her fascination to the power of light—as well as the importance of optimism. 

As her vision cleared, Widder found the intersection of her two passions in oceanic bioluminescence, a little-explored scientific field within Earth’s last great unknown frontier: the deep ocean. With little promise of funding or employment, she leaped at the first opportunity to train as a submersible pilot and dove into the darkness. 

Widder’s first journey into the deep ocean, in a diving suit that resembled a suit of armor, took her to a depth of eight hundred feet. She turned off the lights and witnessed breathtaking underwater fireworks: explosions of bioluminescent activity. Concerns about her future career vanished. She only wanted to know one thing: Why was there so much light down there? 

Below the Edge of Darkness takes readers deep into our planet’s oceans as Widder pursues her questions about one of the most important and widely used forms of communication in nature. In the process, she reveals hidden worlds and a dazzling menagerie of behaviors and animals, from microbes to leviathans, many never before seen or, like the legendary giant squid, never before filmed in their deep-sea lairs. Alongside Widder, we experience life-and-death equipment malfunctions and witness breakthroughs in technology and understanding, all set against a growing awareness of the deteriorating health of our largest and least understood ecosystem. 

A thrilling adventure story as well as a scientific revelation, Below the Edge of Darkness reckons with the complicated and sometimes dangerous realities of exploration. Widder shows us how when we push our boundaries and expand our worlds, discovery and wonder follow. These are the ultimate keys to the ocean’s salvation—and thus to our future on this planet.
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Listen to a sample from Below the Edge of Darkness

Praise for Below the Edge of Darkness

“Gripping . . . Widder’s voice is in turns jaunty, precise and nerdily quippy. . . . The prose glints. . . . Widder [has] worked hard to bring the abyss to light. It is our duty, as clumsy land-bound dwellers of a water planet, to look, and to remember.”The New York Times Book Review

“Edith Widder’s story is one of hardscrabble optimism, two-fisted exploration, and groundbreaking research. She’s done things I dream of doing. I’d have wrapped my submersible, the Deepsea Challenger, in bacon if it would have lured the elusive giant squid from the depths. In Below the Edge of Darkness, Widder tells you how she did it.”—James Cameron

“My experience of exploring the deep ocean and its alien life with Edie Widder was fabulous. She enthralls us with many such stories in her book. I recommend it.”—Ray Dalio

“To shed light on a subject is what any scientific book should do. To go into it in depth without losing the reader is a harder task. Edith Widder’s subject is light itself—the manufacture of light by strange and eerie denizens of the deep sea—and her scintillating style is worthy of the topic. This is a book to delight the general reader while simultaneously informing the professional: a book of marvels, marvelously written.”—Richard Dawkins, New York Times bestselling author of The God Delusion

“Personal and page-turning, adventurous and awe-inspiring, Below the Edge of Darkness sparkles with the thrill of exploration and glows with an urgent plea for the future of our precious seas. Comparisons to Jacques Cousteau spring to mind as Edith Widder shares the profound journey of her life—one as unique and important as the unexplored realms of our very own planet.”—Juli Berwald, author of Spineless: The Science of Jellyfish and the Art of Growing a Backbone

“‘Luminous’—the topic, the heroic journey, and the author herself. Dive in with Edith Widder, trailblazing scientist and explorer, as she reveals the galaxy of light and life in the universe below the surface of the sea, out-shining skeptical male colleagues with dignity, grace and a robust sense of humor.”—Sylvia Earle, National Geographic explorer in residence, founder of Mission Blue
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Below the Edge of Darkness

Chapter 1


Light is what, exactly? For something that has no mass, it sure carries a lot of existential weight. It is both an energy source and an information carrier. It can be injurious and it can be healing. It is one thing that can manifest as two things—a wave in the future and a particle in the past. In a vacuum, it travels at the maximum speed allowed by the universe, and it does so without ever decaying. It gives up its energy only when it interacts with other particles, like those that make up the visual pigments in our eyes, and it is through these interactions that we interpret the world around us.

For most life-forms on Earth, light is the paramount stimulus that makes life as we know it possible. Green plants harness energy from light to synthesize sugar from carbon dioxide and water. In the process, oxygen is generated as a by-product. As magic tricks go, forming food and breathable air from what seems like nothing is hard to beat. Still, it’s not especially flashy. Creating dazzling light from food and air, however, is very flashy. That’s the magic of bioluminescence. Of course, to appreciate that particular alchemy, you need something equally miraculous: vision.

Being able to see provides a huge advantage in the game of life; it is for this evolutionary reason that 95 percent of all animal species on Earth have eyes. These range from microscopic, such as some single-celled algae that have an eye no bigger than one-tenth the diameter of a human hair, to giant squid with an eye the size of your head. The different ways that such disparate eyes see the world reveal much about the biological needs of their owners. In fact, figuring out what different eyes are best adapted to see is such a valuable tool for probing the nature of life that it has become a whole field of study called visual ecology.

If you compare the life of a giant squid inhabiting the deep sea with that of microscopic plankton living in sunlit surface waters, the difference in eye size makes sense: a giant eye collects many more photons than a tiny one and is therefore better adapted for living in a dim light environment. But what about another deep-sea inhabitant, the cockeyed squid? Its name derives from its mismatched eyes: the left eye is giant and bulging and directed upward toward the sunlight, while the right eye is smaller, recessed, and aimed downward into the inky depths. This seemingly makes no sense—until you learn that bioluminescent light organs encircle the small eye. While the large eye hunts overhead for dim, distant silhouettes of prey against a dark, lead-gray background, the bottom eye can use its built-in flashlights to illuminate more proximate prey. Clearly, to understand the visual ecology of the largest living space on Earth, one needs to appreciate the nature and function of bioluminescence alongside the nature and function of eyes.

It is inevitable that when we try to figure out what different animals see, we relate it to what we can see. That is a major challenge in the deep ocean, though, where our very presence alters the visual environment. It’s difficult to envision a place you are unable to observe in its natural state. Our eyes are adapted for a much brighter existence, which means that when we explore darkness, we must bring artificial lights so intense that to visual systems adapted to the deep sea, they are probably as bright as looking directly into the sun. Since it is such a challenge to observe animals in this realm without disturbing them, sometimes the best way to gain insight into their lives is to learn as much as possible about their eyes.

The most important questions to ask about eyes are: What information do they accept, and what do they exclude? All eyes act as filters, allowing in only data streams about the outside world that optimize their owner’s chances for survival. Anything that doesn’t serve that purpose falls under the banner of too much information. Spending time and energy on producing ultraviolet receptors, for example, and processing and interpreting their output is counterproductive if UV light plays no useful role in detecting vital stuff like food, mates, or predators.

Thinking about eyes and what they do and don’t see is a mind-stretching exercise. We are blind to so many things in our world—some because of biological constraints, and many more because we simply don’t know how to look. Environmentalist Rachel Carson once said, “One way to open your eyes to unnoticed beauty is to ask yourself, What if I had never seen this before? What if I knew I would never see it again? ” An even better way to achieve heightened visual awareness is to lose sight and then regain it. As Joni Mitchell sang, “Don’t it always seem to go, that you don’t know what you’ve got till it’s gone?”

That Joni Mitchell song, “Big Yellow Taxi,” was released my first year in college. I started at Tufts University in the fall of 1969 as a biology major, with the aim of becoming a marine biologist. But before I had completed my first semester, it was clear that goal would be unattainable without medical intervention. During my precollege physical, I mentioned a pain I’d been having down the back of my left leg. Since I was pretty active—a skier and skater in the winter and a water skier in the summer—I figured I must have pulled a muscle. X-rays revealed otherwise: My back was broken. The doctor illustrated the extent of the break by making two fists with his hands, stacking one on top of the other, and then sliding the top one halfway off the bottom one. The slippage was pinching a nerve going down my left leg, causing the intense and persistent pain I felt whenever I sat down.

I’m pretty sure I know when I broke it. I spent a lot of my childhood climbing up into and jumping out of trees in our leafy suburban neighborhood just outside Boston. My favorite tree was an old misshapen willow down by the pond near our house. Its trunk ramped up at a forty-five-degree angle away from the water and then branched into two large horizontal limbs, each with thick vertical branches that created separate “rooms” that made it the perfect pirate ship, tree house, or castle. The limbs were about seven feet off the ground: a comfortable jump that I made hundreds of times with ease. But I remember one Sunday, when I was eight or nine years old and dressed for Sunday school in some stupid frilly dress I hated, the jump didn’t go as planned.

When we came back from church, I couldn’t change into my beloved jeans, because we were going someplace fancy later, but I was allowed to be outside until it was time to go, as long as I promised to stay clean. I wandered off to climb my favorite tree, but when I went to jump down, I remembered my promise and landed in a way that protected my dress instead of myself. A searing pain ripped through my back—like nothing I’d felt before. But it didn’t last long, and I shrugged it off.

Until that college physical, I thought low back pain was something everybody had. I couldn’t remember a time without it. By my first semester at Tufts, it was so bad that I couldn’t stand for any extended period, and sitting was equally miserable because of the pain in my leg. The only way I could do homework was by lying flat on my back with a pillow under my knees. This was not conducive to good study habits, as I would often fall asleep and bonk myself in the face with whatever tome I was attempting to wade through—a very effective form of negative conditioning. When it became clear I couldn’t go on like this, a spinal fusion was scheduled for the beginning of February.

According to the Urban Dictionary, “crumping” is a slang medical term indicating that a patient’s condition is rapidly worsening. See also: “circling the drain.”

I crumped; not during the spinal fusion, which went fine, but afterwards, in the recovery room. I went from okay to Oh shit in a New York minute, flipping around in the bed like a fish on a dock while hemorrhaging nearly everywhere. I had a blood disorder called disseminated intravascular coagulation (DIC). The cause is unknown, but it’s often associated with major trauma and manifests as overactive clotting factors in the blood, causing clots to form in the small blood vessels of the body, blocking blood flow to vital organs. In extreme cases, the clotting factors and platelets are consumed to such a degree that severe bleeding ensues. The result, in my case, was that I wasn’t just bleeding into my surgical sites but also into my lungs, depriving me of air, hence the fish-out-of-water imitation.

Two factors conspired to allow me to survive this medical Armageddon. In fact, I was the first person ever to survive it at Mount Auburn Hospital. The first was that my orthopedic surgeon had recently attended an American Medical Association conference on DIC, which allowed him to recognize the symptoms. Usually, a doctor who sees his patient hemorrhaging will administer coagulants to stop the bleeding, but that just leads to more clotting in the small blood vessels and increased likelihood of organ failure. Instead, my surgeon knew to give me the anticoagulant heparin, thereby averting organ failure but greatly exacerbating the bleeding problem.

The second lucky break was that the famous Harken “chest team” happened to be at Mount Auburn that day. The chest team’s first order of business was to start my heart, which had stopped.

About the Author

Edith Widder, Ph.D.
Edith Widder, Ph.D., is an oceanographer, a marine biologist, and the co-founder, CEO, and senior scientist at the Ocean Research & Conservation Association, a nonprofit organization where she is focusing her passion for saving the ocean into developing innovative technologies to preserve and protect the ocean’s most precious real estate: its estuaries. She has given three TED talks; has been awarded a prestigious MacArthur Fellowship from the John D. and Catherine T. MacArthur Foundation, as well as the Explorer’s Club Citation of Merit; and is the first recipient of the Captain Don Walsh Award for Ocean Exploration established by the Marine Technology Society and the Society of Underwater Technology. More by Edith Widder, Ph.D.
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