April 20, 2012

Bioluminescence, or cold chemical light made by living creatures, answers a simple question: how can an animal survive in the dark? Making its own light by which it can find food, attract mates or defend itself against predators is an easy fix. This phenomenon has evolved at least 40 times in evolutionary history—a clear indication of how important the trait is for various animals’ survival.

Edie Widder, president and senior scientist at the ocean conservation organization ORCA, has dedicated her career to studying bioluminescence. “Everywhere we look in the ocean, we find animals that make light,” she said. “If we drag a net through the ocean almost anywhere, in many places 80 to 90 percent of the animals will be bioluminescent. It’s crazy,” she described.

Animals evolve bioluminescence for a variety of reasons. On land, fireflies use bioluminescence to attract mates using specific flash patterns. But in the ocean, bioluminescence is most commonly used as a defense or as a way to find food.

Much like an octopus uses its ink, some species of fish, shrimp, squid and jellyfish will release a spray of bioluminescence into a predator’s face to momentarily blind the carnivore while they escape into the darkness.  Other fish use bioluminescent lures to trick smaller creatures into willingly following the light into the predator’s gaping jaws. Flashy bioluminescence also serves as a warning. Just as a monarch butterfly displays its toxicity through bright wing patters, a bioluminescent ocean species can advertise its non-palatability with light.

In the so-called twilight region of the ocean—the area 200 to 1,000 meters deep where sunlight still penetrates, but just barely—predators often find prey by looking up and spotting a tasty morsel’s silhouette against the sunlight. To counter this strategy, prey species have evolved bioluminescent bellies. Called counter illumination, their undersides mimic the exact intensity of sunlight. If a cloud passes overhead, for example, their bioluminescent camouflage dims.

Finally, many animals use bioluminescence to pull off an ecological strategy called a burglar alarm. Just as a thief breaking into a car may flee when the vehicle’s flashing lights and blaring horn advertises his crime, as a last resort, some species of animals attempt to draw attention to themselves if they’re captured by a predator. A jellyfish caught in a predator’s jaws may turn on all of its lights in a bright display, hoping to attract an even larger predator that may turn the tables on who-eats-who. “It’s a way of using light to scream for help,” Widder said.

Widder first became interested in bioluminescence as a post-doc in 1982. She took part in a series of deep-water dives in the Santa Barbara Channel, utilizing in a diving suit called the Wasp. At about 880 feet down during an evening plunge, she turned out the lights on her suit. “I was just blown away by the light show,” she recalled. Knowing how much energy light production requires, she realized that bioluminescence must be a very important biological process in the ocean. At the time, however, few people researched the phenomenon since technology for studying it was rudimentary. Since then, much of Widder’s career has been spent developing the tools that will allow her and other scientists to quantify bioluminescent light.

For starters, she created a camera system attached to an optical lure that imitates certain bioluminescent displays to see how animals respond. Dropping the device off the back of a ship, it can sink up to 2,000 meters to study the organisms below.

Until recently, Widder said, “The only way knew what lives in the ocean is to drag nets behind ships or go out with bright, noisy submersibles and remotely operated underwater vehicles that scare animals off. The solution is camera systems.”

She modeled another camera on a deep-sea fish that has three different lights under each of its eyes: one blue high beam and two red lights. The fish emits the red light, which many species cannot detect, like a sniper scope. Widder modeled her camera system, dubbed the Eye-in-the-Sea, after the animal. The first time she used it in 2004 in the Gulf of Mexico, within two minutes the camera captured an image of a large squid so new to science that its phylogeny couldn’t be classified. Similar systems are now being used to explore the waters of the Bahamas and Japan.

Widder points out that she finds it surprising that ocean bioluminescence is so ubiquitous, yet so few people know anything about it. The most plentiful vertebrate on earth, for example, is a little bioluminescent fish called the benttooth bristlemouth. Given how common bioluminescence is, she pointed out, “If aliens come from space to see what kind of life is on Earth, they might think our prominent form of communication is light.”

For those interested in seeing bioluminescence firsthand, Puerto Rico’s bioluminescent bays provide year-round access. The Sea of Cortez also contains about 200 meters of bioluminescent larvae giving it an ethereal glow. Off the coast of California, a temporary dinoflagellate bloom is providing residents with beautiful light shows, too.

For New York City residents or visitors, the American Museum of Natural History currently has a bioluminescence exhibition called Creatures of Light, featured until January 6, 2013. And Widder herself will be on display at the museum this Sunday, eager to answer questions for curious Earth Day museumgoers.

Top Image Credit: E. Widder

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