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.
Pachystomias microdon: A species of dragonfish with red light-emitting photophores.
E. Widder/Orca
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.
The light-emitting jellyfishAtolla wyvillei
E. Widder/Orca
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.”
