Is eyeless sea creature fishing with a red light?

Scientists working in waters off California have captured deep-sea jellyfish relatives waving little spikes that glow red.

RED ROVER. One of the siphonophores (above) of genus Erenna, which has no eyes itself, flickers with little red lights among its stinging tentacles (below). Monterey Bay Aquarium Research Institute

Monterey Bay Aquarium Research Institute

In the black ocean depths, plenty of creatures glow, but most of those that had been examined shine in blues and greens, says Steven H.D. Haddock of Monterey Bay Aquarium Research Institute in Moss Landing, Calif. He notes that biologists have assumed that deep-sea creatures can’t see red wavelengths, which don’t travel far underwater. Haddock names only one other group of red-luminescing marine animals, the scaleless dragonfish.

The latest creatures to enter the red zone are siphonophores of the genus Erenna. Each can be considered a colony of individuals strung together like a feather boa. Although they don’t have eyes, they prey on small animals. At depths of 1,600 meters or more, Haddock and his colleagues used a remotely operated vehicle to study three of the fragile siphonophores. Among their stinging cells are stalks with glowing, paddle-shaped ends.

The researchers suggest that this red glow isn’t defensive. Other marine creatures that luminesce when threatened typically burst out in a brief, bright display. The siphonophores, however, produce a twinkling effect by twitching their glowing tips back and forth.

The animals that Haddock caught had been eating fish, even though copepods are a more common prey for siphonophores. The little red lights could work as lures, he and his colleagues propose in the July 8 Science. That would require that their prey see red, but the researchers point out that scientists haven’t studied eye physiology of fish that are Erenna prey.

Susan Milius is the life sciences writer, covering organismal biology and evolution, and has a special passion for plants, fungi and invertebrates. She studied biology and English literature.

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