July 7, 2005

Red Light-Flashing Jellyfish Lures Prey

WASHINGTON -- The first deep sea red-light district - glowing appendages on a newly discovered jellyfish relative - appear to flash their come-hither message to lure prey.

Jellyfish and other types of sea creatures are known to produce light, but this is the first deep ocean invertebrate known to use red fluorescent light, said Steven H. D. Haddock of the Monterey Bay Aquarium Research Institute in Moss Landing, Calif.

Three of the animals were found by scientists using a remote controlled research vehicle at depths of between 5,200 feet and 7,500 feet off the coast of California. The discovery is reported in Friday's issue of the journal Science.

The new find is a previously unreported species in the genus Erenna, which is a member of the group that includes coral and jellyfish.

The animal, which has not yet been named, has tentacles with side branches that consist of stinging cells attached to a central stalk.

The researchers said that inside the stalk are spots that produce blue-green light when immature and red light when mature.

And they noted that the two colors are produced by different methods. The blue-green light is produced by a process called bioluminescence, which emits energy as light instead of heat. The red light comes from fluorescence, a process in which short-wavelength light such as blue is re-emitted as long-wavelength red light.

There are not many fish at the depth where the specimens were found, but two of the Erennas had fish inside them.

Based on the shape, size and motion of the tentacles, and the fish found in the stomachs, Haddock said the researchers believe the red lights are being used to attract fish that can then be captured and eaten.

Stephen D. Cairns, a research scientist at the Smithsonian's National Museum of Natural History, called the discovery a "quaint example of a primitive life form (a jellyfish, an organism without a brain), outwitting a vertebrate - a deep-water fish in this case - by mimicking the red light the fish is purported to emit."

"This is another fascinating case of deep-sea ecology, an event that probably happens millions or billions of times a day, but one that we glimpse for the first time only now," said Cairns, who was not part of Haddock's research team.

Previously many scientists had thought that most fish living at this depth could not see red light, Haddock said in a telephone interview.

At this depth, the ocean filters out red, leaving only blue-green light, he said, and studies of some fish and shrimp eyes indicated a lack of sensors for red wavelengths.

But, he said, there is evidence that some fish can see red, possibly giving them an advantage in finding certain organisms to eat that are red.

The research was funded by the Packard Foundation and the National Science Foundation.


On the Net:

Science: http://www.sciencemag.org/

Monterey Bar Aquarium Research Institute: http://www.mbari.org