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Wednesday, March 10, 1999 Published at 19:06 GMT


Sci/Tech

Shrimps blinded by science

The shrimp's specially adapted eye occupies about half of its back

Shrimps are literally being blinded by science, British biologists believe.


Edward Gaten describes the fate of the shrimps
Deep-sea submarines exploring the dark depths of the Atlantic Ocean use powerful floodlights to illuminate their way. But these lights are destroying the remarkable eyes of the shrimps that live there.

The biologists vacuumed up shrimps from the ocean floor into a blackout chamber. In the laboratory, they found that some had shiny pink eyes whilst others had matt, chalky white eyes.


[ image: Shrimps swarm over the vent chimneys]
Shrimps swarm over the vent chimneys
Peter Herring, at Southampton Oceanography Centre, got the shrimps from the sea floor 3km under the Atlantic. He asked Edward Gaten and Peter Shelton, at Leicester University, to examine them.

Dr Gaten told BBC News Online: "I found the white ones had no photosensitive layer left. What effectively is the retina had been completely destroyed."

"This was almost certainly caused by the bright searchlights on the submersibles that scientists use to sample the vents. It's an unfortunate case of scientists blinding the shrimps without realising it."

Unreliable behaviour

This discovery means that previous observations of the shrimps' behaviour around the vents may not be reliable, as their eyesight, "exquisitely adapted for dim conditions" had been destroyed.


[ image: The healthy pink eyes and destroyed white eyes, both about 2mm long]
The healthy pink eyes and destroyed white eyes, both about 2mm long
The shrimps rely on the bacteria that thrive at the vent for food. Their eyes, which take up half their back, are specially adapted to seek out the vent. However, all is not lost, as the blind shrimps should be able to smell their way to the sulphurous vents.

Using searchlights is unavoidable at the moment says Dr Gaten: "You can't do anything else. It's a very dangerous place at the bottom of the sea, with the rough volcanic landscape, and pilots must have strong lights to see.

"We have suggested using infrared for navigation near the vents, and also suggested using side-scan sonar. But these are expensive to develop and the pilots really want to see. I certainly wouldn't go down there without plenty of lights."

The shrimps, from the Bresiliidae family, were collected at the Rainbow site on the Mid-Atlantic Ridge, a volcanically-active place where the Earth's crust is splitting apart.

The biologists believe the damage takes up to a few weeks to sink in. This would explain why both seeing (pink-eyed) and blind (white-eyed) shrimps were found. The site had been visited a month before, so those caught in the headlights then were now blind. Those lucky to escape still had working pink eyes.

The study is published in Nature.



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