The Science Channel show Brink recently produced a segment based on this DISCOVER story; see the video below.

For a human, the deep sea is as alien as deep space. Go down several hundred feet into the ocean and the world is dark blue. Another thousand feet and your surroundings have faded to a dim bluish-gray twilight. There is enough illumination for a person to see at that depth, but too little for photosynthesis. Descend through this twilight zone another thousand feet and it is eternal night.

The darkness is not truly dark, however, and the seeming emptiness is actually full of secret messages: About 80 to 90 percent of deep-sea animals use chemicals to create bioluminescent light, piercing the gloom with signals in blue and green, orange and yellow. When it comes to understanding who is flashing whom and what it all means, though, we might as well be trying to eavesdrop on an extraterrestrial conversation.

For decades marine biologists have gotten glimpses of this glittering life by casting nets and retrieving deep-sea organisms. More recently they have lowered cameras on cables and measured the bioluminescence on display beneath the waves. Using special diving suits and submersibles, they have even entered the habitat of deep-sea organisms, watching in awe as the water world lit up with bursts of color that sparkled like fireworks. From these studies researchers have been able to glean a few basic details about bioluminescence. They know that luminescent displays signal the best mates, point the way to food, and warn of danger. The bioluminescent hatchetfish, for instance, uses its light to hide from predators by mimicking sunlight filtering through the water; the shining tubeshoulder uses bioluminescence to startle predators.

But understanding the meaning of the flashes produced by the wide swath of bioluminescent species has been impeded by one simple fact: Diving suits and submersibles frighten sea organisms, disrupting their natural behavior exactly when scientists are there to observe it. Without the ability to watch sea life undisturbed in its habitat, we have been unable to piece together the vocabulary, the grammar, or the syntax of this enigmatic language of light.

That may soon change, courtesy of Edie Widder, a cofounder of the Ocean Research & Conservation Association (ORCA) and a specialist in marine bioluminescence. She has developed a spy camera for the deep, dubbed Eye-in-the-Sea, that is opening a window on this hidden world. The Eye sits on the ocean floor and quietly records bioluminescent organisms in their natural habitat without scaring them. Like the Search for Extraterrestrial Intelligence (SETI), Widder’s work is a bold attempt to make contact with creatures from another world. Only in this case, we know the aliens are among us.

Seeing the Light
While studying neurobiology at the University of California at Santa Barbara in the early 1980s, Widder boarded a ship and set out to sea. She was trained as a neuroscientist, but her specialty made her a good fit for the voyage: For her Ph.D. she had studied the neurological signal that triggers the flash of bioluminescence in dinoflagellates (mostly single-celled plankton living in oceans or lakes). Widder was thus well prepared to operate one of the scientific instruments on board, a supersensitive spectrometer that measures the color of light. To help Widder study the glowing creatures, other scientists with dive experience donned state-of-the-art suits and collected samples for her to test with the device. But when she asked the divers to describe what they saw down there, words failed them. “All I would get was ‘Wow!’?” she says. So she learned how to operate the suits and began diving herself.

On her first dive, Widder descended to 880 feet, turned off her flashlight, and watched the sparkling display of colored lights bursting around her. “Everything was lighting up and in spectacular ways,” she remembers. A 30-foot-long siphonophore—which looks like a colony of jellyfish—was putting out so much light that Widder could read the dials and gauges inside her suit without her flashlight. She remembers thinking that given the huge number of animals using bioluminescence, it must be “one of the most important processes in the ocean, and yet hardly anyone was studying it.”

In its most basic form, Widder says, bioluminescence might have evolved as “an adaptation to life in dim-light environments.” It is most common in the open ocean, where organisms have nowhere but the darkest, deepest depths in which to hide. Animals that navigate through vision still need light to guide them, however. Their solution: built-in flashlights and illuminated lures that turn on when it is safe but can be shut down when danger appears.

Biologists know that animals use bioluminescence to survive in other ways as well—to attract mates, lure prey, startle predators, and even attract bigger predators that come swooping in to grab the smaller predators, thus sparing the initial prey. Some animals—for instance the cyclothone, the most common vertebrate in the world—even use light as camouflage during the day as they move about more than 1,000 feet beneath the surface. “The animals emit a remarkably effective dim glow from their bellies that exactly matches the intensity and color of sunlight penetrating from the surface,” Widder explains, “so they aren’t easily seen by predators swimming below them.”

At night these same animals venture up near the surface in what may be the greatest migration in the animal kingdom. “There are no trees or bushes for animals to hide behind in the ocean,” Widder says, “and yet they have to play all the games of hide-and-seek that animals do on land. Prey needs to hide from predators, and predators need to sneak up on prey. So a lot of animals engage in a vertical migration, going down and hiding in the dark depths during the day and coming up and feeding during the night.”

But there is still much to be learned about how and when animals light up. One way of doing this is to imitate the signals and watch for a response. On one dive, Widder carried a blue light affixed to the end of a long pole. “I tried to use light to see if animals would talk back to me,” she says. She did not see any responses and realized it was “naive to think that I was unobtrusive dangling at the end of this cable.”

View From the Brine Pool
That experience spurred Widder, a longtime gadget freak, to design the Eye-in-the-Sea. She worked with a team of engineers to outfit a battery-powered camera system with a supersensitive light detector called a photomultiplier tube. She enclosed all of it in a cylinder sturdy enough to withstand the intense water pressure found at 3,000 feet. To see the animals as they moved by the lens, Widder used a red light that is invisible to most deep-sea creatures, whose eyes are tuned to see primarily blue. She added a clamp to hold dead fish that would serve as bait to draw animals into camera range.

Widder also designed a lure to mimic the light patterns of the Atolla wyvillei, a common deep-sea bioluminescent jellyfish. She and other researchers had observed these jellies and hypothesized that they use their light as a kind of burglar alarm, glowing with brilliant blue bursts in a pinwheel pattern when under attack. “If the jellyfish is in the clutches of a predator,” Widder says, “its only hope for escape is to attract so much attention that it will bring in an even larger predator that will go after the one attacking it. It is so bright it can be seen 100 meters away. So my thinking was that the lure would attract predators.”

Widder was right. In 2004 her Eye-in-the-Sea was lowered into the Gulf of Mexico. It was positioned at the edge of a strange geologic anomaly called the Brine Pool, an underwater lake (about 2,000 feet down) that formed when salts percolated upward from the ocean floor. Because this salt-saturated water is much denser than seawater, it remains an intact pool with defined shores and observable waves. As oceanographer Mandy Joye of the University of Georgia put it as she watched a clearly distinct white wave make its way through the lake, “If you didn’t know better, you would swear it was not underwater.”

The Brine Pool has streams of methane bubbling up through it. Huge colonies of bacteria feed on the methane, and large numbers of clams and worms feed on the bacteria. Topping off the food chain are fish that eat the worms, and then sharks that prey on the fish. This “oasis at the bottom of the ocean,” as Widder calls it, is also a hotbed of activity for bioluminescent animals, which is why she placed her camera there. It was, Widder knew, a perfect spot to test the optical lure.

Initially, researchers saw nothing but a grainy black-and-white scene with the camera’s single light beaming into an empty darkness. But a little more than a minute after turning on the lure’s lights, Widder saw a response. A large squid, more than six feet long, suddenly swooped down on the lure. “It was breathtaking,” she says. After studying the video, she and other scientists realized that the squid was a species new to science. It was more than even Widder could have hoped for.

A year after that first test, Widder went back to the Gulf of Mexico with the Eye, this time programming the lure to emit rapid flashes of blue light to mimic a different type of jellyfish. Again a large squid, perhaps the same species as the first, darted at it. Then she wondered: Would alternate patterns of light imitating other bioluminescent species elicit different types of responses? Hoping to answer that question in 2007 on an expedition off the coast of the Bahamas, Widder set the lure so that it glowed with a single blue light, imitating the light emitted by bacteria that often cover carrion on the seafloor. This time a number of giant, six-gilled sharks appeared, and several of them attacked the lure. Widder then reprogrammed the lure to flash, and the camera captured an animal in the distance seemingly moving in response. “We think it was a deep-sea shrimp, and my best guess is that it was a mating response,” Widder says.

The Spy That Never Sleeps
Turning guesswork into a true understanding of the language of bioluminescence will require much more data. Some of that promises to come from a new version of the Eye that was deployed in January as part of the Monterey Accelerated Research System (MARS), an underwater observatory in Monterey Bay off the coast of California. The MARS observatory, a metal structure with a base measuring about 12 feet by 15 feet, rests quietly on the ocean floor and provides a docking station for the Eye. Connected by a power cable from shore, the Eye is active round the clock, sending back information about life more than half a mile under the sea. “We control the Eye from shore,” Widder says. “We are also using an electronic jellyfish [which mimics bioluminescence] and various sensors to observe naturally occurring activity. It is our first real window into the deep sea, and it is going to be open all the time.”

The MARS version of the Eye presents an unfamiliar problem for Widder: too much data. “We can’t look at it all,” she says. In response, engineers at the Monterey Bay Aquarium Research Institute have developed image-analysis software to detect activity, so the camera records only when something is moving past it. Those segments are then posted online. Widder and others are analyzing these images from their labs; they are also working with educators to incorporate the video into their curricula so students can watch the images and post observations. “The Monterey Canyon isn’t quite as rich an area as a place like the Brine Pool,” Widder says, “but we should have a chance to figure out more about what bioluminescent animals are saying to each other.”

Findings from other camera systems are helping to fill in our picture of deep-sea communication. Scientists at the University of Aberdeen in Scotland are running experiments with an automated submersible that has a camera designed to record bioluminescent signals as it descends through the ocean and lands on the seafloor. And in 2005, Tsunemi Kubodera, a zoologist at the National Science Museum in Japan, used a high-definition video system to study the elusive Taningia danae, a huge, eight-armed, bioluminescent squid that exceeds seven feet in length. In a series of experiments, Kubodera’s camera system was suspended from ships near Chichijima Island in the North Pacific and recorded video at various depths, down to 3,100 feet. It captured the first live images of Taningia in its natural habitat.

Like Widder’s Eye, Kubodera’s system carried bait and used colored light to attract predators. One or two torchlights were also attached to the bait rigging. Kubodera’s videos, which captured 14 attack behaviors, showed that as a squid approached, it sometimes emitted a short flash from photophores (light-producing organs) on the tips of its arms, perhaps in an effort to blind its prey or to illuminate it for easier capture. Most interesting to the researchers, the squid sometimes produced a long glow and several short ones as it swam around the bait but did not attack. “We believe that this behavior may represent attempts at communication,” the researchers write. The light given off by the torches attached to the bait, they suggested, may resemble the long glow of a squid’s photophores, leading it to believe it was approaching a potential mate. When the torchlights didn’t respond to the squid’s signal, the animal moved on.

Even as scientists begin to decipher the light signals of deep ocean life, their work may be threatened by the onslaught of human disruptions—everything from sonar to carbon dioxide, which causes acidification. That is one reason why Widder plans to take a version of her technology to Australia to explore a region that is relatively pristine and has never been visited by submersibles. As a cofounder of ORCA, devoted to scientific inquiry about the health of the world’s oceans, she recognizes that time is of the essence for studying as much of the deep-sea ecosystem as she can right now.

The earth’s oceans are not just fragile but forbidding, as difficult to study as distant galaxies. Like the Hubble Space Telescope, the Eye-in-the-Sea is a promising step toward bringing that world into view. It is, as Widder’s colleague Sönke Johnsen says, “a new way to get inside the mind of nature.” Thanks to Widder and others, the secret messages of the sea’s most elusive creatures may not remain secret for long.