Jellyfish lures dinner with flashing red light
Scientists discover unusual power in simple sea creature
By Marsha Walton
A deep sea relative of the jellyfish produces a red luminescent light.
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Flashing red lights often mean danger. And that seems to be true whether it's on a highway or a mile below the surface of the Pacific Ocean.
Scientists have discovered a jellyfish-like creature, a type of siphonophore, that has a glowing red appendage that acts to lure fish, which the animal captures with its stinging cells and then eats.
The unusual biological structure, known as a tentilla, intrigued scientist Steven Haddock, of the Monterey Bay Aquarium Research Institute in Moss Landing, California.
He and other scientists watched the red glow on the minuscule body part in a dark lab onboard their research ship.
"You actually got adrenalin going. You wouldn't think [a jellyfish] would get your heart rate up, but it was pretty exciting. It's one of the most tangible benefits of being a scientist," said Haddock.
The red "lights," the first ever observed on a marine invertebrate, were just a couple of millimeters in length, and mysterious for another reason: Scientists have generally believed that animals in the deepest parts of the ocean could not detect red light.
Bioluminescence, which is the emission of light from a living organism, is well recognized in the marine world. Usually it is in the form of a blue-green light produced as a defensive mechanism, often to distract predators. It's a fairly common trait among siphonophores. Red light comes from another process called fluorescence, when the short wavelength blue light is re-emitted as red, or long wavelength light.
Haddock described the tiny lure mechanism as something like a Tootsie Pop. In the core of the lure, the blue green light is emitted. It is covered by a red material, so when the light is triggered, it passes through this red surface. The wavelength of the light is converted, and looks orangy-red on the outside.
Studying deep sea jellyfish is a challenging field of research because of the depth where some of these creatures live and their fragility. There are about 160 species of siphonophores, and they include the longest creatures on Earth, some as long as 120 feet. But they can break apart with even the slightest force.
Haddock and his colleagues collected three specimens, between 40 and 100 miles off the west coast of the U.S. and Mexico. The creatures, about a foot and a half long, were caught in canisters deployed and retrieved by a remotely controlled submersible. They were living between a mile and a mile and a half below sea level.
Because of the new information, Haddock says scientists may next look at how eyes work in the type of fish that these jellyfish are luring, to see how they respond to red and other colors of light.
And he says it just adds to his interest in the remarkable adaptiveness of these "big jellies."
"It's amazing how much detail you can get [in these animals] without any actual thought going into it," he said.
Jellyfish do not have brains. Instead they have a simple nervous system called a "nerve net" throughout their bodies, enabling them to swim and eat in a coordinated fashion.
The research is published in the journal "Science."
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