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Oceans of Light

A deep-sea explorer, winner of a 2006 MacArthur “genius grant,” is solving the mysteries of a strange, luminous realm
Article and Photographs by Edith Widder, J73

In the early 1980s, fresh out of graduate school, I had an opportunity to pilot a self-propelled deep-diving suit, the Wasp, that could travel 2,000 feet beneath the waves. That experience opened my eyes to the amazing creatures that use bioluminescence—chemically produced light—to survive in the ocean.

On land, animals that can glow, à la fireflies, are rare. At sea, they are the rule rather than the exception: 80 to 90 percent of creatures in the open ocean make light. Although in coastal waters only about 10 percent of species are bioluminescent, they can occur in vast numbers, like the glowing dinoflagellates that cause some red tides. I realized after that first dive in the Wasp that bioluminescence had to be one of the most important processes in the ocean, and I wanted to learn everything I could about it.

I have spent much of my career working with engineers to develop instruments that help me study how animals use their light-making ability to find food, attract mates, and defend against predators. Recently, through a nonprofit I founded called the Ocean Research & Conservation Association (www.oceanrecon.org), I have begun exploring another dimension of light: bioluminescence is one of several indicators we can monitor to determine the health of ocean ecosystems.

To study bioluminescent creatures close up, we must catch specimens at icy depths—sometimes thousands of meters down—and bring them up to a research ship without killing them in the warm surface water (the huge pressure difference is less of a problem, because few of these animals have air-filled sacs to overinflate). We have two ways of collecting them. One way is to use a net outfitted with an insulating device. The other is to pilot a submersible that scoops up specimens in sealed Plexiglas cylinders. Aboard ship, I study the animals in a darkroom equipped with special cameras that work in dim light and are ultrasensitive to blue, the most popular color for ocean bioluminescence.

Sniper vision. Bioluminescence comes in all colors: red, orange, yellow, green, blue, and violet. But since blue is the color that penetrates farthest through water, it is not surprising that it is the color that evolution has selected most often both for emitters (bioluminescence) and for receivers (eyes). Among the exceptions is this scaleless dragonfish (Pachystomias microdon), shown at top, which has three different headlights under each eye. The blue headlights are thought to be used like high beams for seeing at great distances. The red headlights apparently serve as a sniper scope. That’s because the dragonfish can use them to sneak up on prey that can see only blue. Why are there two sets of red lights? No one knows.

Hook, line, and sinker. In the dark depths of the ocean it’s difficult to find both food and mates. This anglerfish—species unknown—attracts both with a glowing lure attached to a fishing pole atop her head. To attract food, she dangles the light in front of her mouth. Scientists once believed the lures’ elaborate shapes were intended to attract different prey. Now it is believed that the shape helps males identify females of their own species.

Anglerfish have one of the planet’s more bizarre mating arrangements. An adult male latches onto a female—who is more than 10 times his size—and becomes permanently attached (second photo). Having a permanent mate allows the fish to avoid the difficult task of repeatedly searching for a partner in the dark waters 300 to 6,000 feet beneath the surface.

Images such as this one are extremely rare. This pair of Melanocetus was collected during an expedition off the northwest coast of Africa for the Blue Planet TV series, on which I served as a consultant.

Smoke screen. Many animals in the ocean fend off attackers by squirting out a blinding cloud, much the way a squid distracts predators with a cloud of ink. This shrimp (Acanthephyra) vomits bioluminescent material onto its attacker and then tail-flips backwards into the darkness. I assembled this photo from three separate images—the shrimp, the viperfish, and the luminous cloud—all shot under different lighting conditions.

Underwater fireworks. The rainbow zipper (Euplokamis) propels itself with tiny combs whose tightly spaced teeth beat against the water. The rainbow appears because the combs act like little diffraction gratings, breaking the white light into individual colors. When bumped and viewed with the lights out, the zipper releases a cascade of bioluminescent sparks as well as a steady glow from its comb rows.

Retractable headlights. Like a deep-sea Lamborghini, this rat-trap fish (Photostomias guernei) can retract its headlights. The lights on its cheeks probably help the fish locate prey in the dark. They may also play a role in mate selection, since the light organs of males are much larger than those of females. This specimen is a female. Just like the headlights on a car, these light organs can be flashed on and off. But even in the “off” state, the lights are so reflective they could betray the fish’s presence to predator or prey. That’s why the fish rolls the light organs out of sight when they’re not in use—all the better to blend into the inky black depths. This sequence of images (top to bottom) is the first time one of these fish has ever been caught in the act.

Cries for help. If caught in the clutches of a predator, the only hope for some animals is to attract the attention of a larger predator that will attack their attacker. Periphylla periphylla, perhaps the most abundant of all deep-sea jellyfish, appears to use its blue light as just such a burglar alarm.

Another deep-sea jellyfish, Atolla wyvillei (third photo), signals to large predators by producing a pinwheel of blue lights that rotate around its bell. This beacon is so effective that we built an electronic version out of blue LEDs, in hopes of luring large animals to study. Within seconds of activating the LEDs for the first time, we attracted a previously unknown species of squid.

Cloak of invisibility. Many animals in the ocean have bioluminescent light organs that they use to disguise their silhouettes. Because seawater scatters light, the point patterns on this squid of the genus Abralia tend to blur at a distance. When that happens, the bioluminescence exactly matches the color and intensity of the dim blue light filtering down from above, so these animals can hide, even in the open ocean.

Squaring off. Some animals use their bioluminescence to warn predators that they are toxic. I believe that is what this jellyfish, known as Clytia languidum, is doing. I collected it with a submersible at about 2,800 feet deep off the Bahamas. When I touched it, its body changed into a square, and it lit up green. A square is a very unusual form in nature. I imagine it being akin to a skull and crossbones, warning, “Don’t eat me or you’ll be sorry!” The first two photos are with the lights on; the third is with the lights off.

So long, suckers. I was surprised to discover that the beautiful red octopus Stauroteuthis has bioluminescent suckers. The editors of Nature were impressed enough with this example of “evolution caught in the act”—suckers turning into light organs—to feature the animal on their cover. Having observed its behavior from a submersible, I believe it uses its bioluminescence to attract its primary food source: tiny crustaceans called copepods that are so common they are like the insects of the sea. The octopus spreads out its arms and flickers its suckers to attract the copepods. Then it forms itself into a big red balloon, surrounding the copepods with its web and drawing them down into its mouth.

EDITH WIDDER, J73, cried when she left the Lerner Marine Lab in the Bahamas, where she spent a month during her junior year at Tufts studying tropical marine biology. But she was soon exploring the oceans full time. With a master’s in biochemistry and a Ph.D. in neurobiology from the University of California at Santa Barbara, she began studying bioluminescent sea life and developed new technologies for viewing deep-ocean creatures unobtrusively. Those efforts and her work on conservation—she founded the Ocean Research and Conservation Association in 2005—earned her a MacArthur Fellowship, or “genius grant,” in 2006.