Science / Medicine : Deep-Sea Shrimp See Without Eyes, Report Says

Eyeless shrimp that live in the pitch-black darkness near hot submarine vents in the Atlantic Ocean have light-sensitive patches on their backs that allow them to see the very low levels of light emitted by superheated water, researchers said in a paper published last week in the British journal Nature.

The eye patches, the only ones of their kind known, apparently allow the shrimp to feed on bacteria and other microorganisms that live near the thermal vents without wandering into the superheated water itself and becoming “instantly pressure-cooked,” the researchers said.

In a second paper, researchers reported that the eye patches are about 10 times as sensitive as human eyes to low levels of light.

The 2-mile-deep submarine vents, discovered only this decade by deep-diving submersibles such as the research submarine Alvin, emit plumes of water at temperatures as high as 660 degrees Fahrenheit, as well as large quantities of hydrogen sulfide. Bacteria feed on the hydrogen sulfide, and they themselves serve as food for a variety of exotic creatures.

At vents in the Pacific Ocean, researchers have discovered clams, mussels and brilliantly colored tube worms several feet in length. For reasons that are not yet clear, the Atlantic Ocean vents seem to be populated by different species, mainly shrimp-like crustaceans.

The most common species is Rimicaris exoculata, which does not have the eyestalks and eyes found on normal shrimp. The 2-inch-long shrimp live in high densities around the vents, moving around constantly in search of food, said biological oceanographer Cindy Lee Van Dover of the Woods Hole (Mass.) Oceanographic Institution.

In her studies of how the shrimp feed, Van Dover was watching underwater movies of them “when I noticed bright, reflective patches on their backs,” she said in a telephone interview. She and her colleagues discovered that the patches are composed of a visual pigment called rhodopsin, found in most vertebrate animals, and covered by a flat transparent surface. Inside the shrimp, a thick bundle of nerves connects the patches to the brain in the same way that eyes are connected.

The researchers became convinced that the eyes are meant to see the superheated water, which like any heated object emits very low amounts of light. Oceanographers who had dived in the Alvin reported that they were unable to see the plumes when they turned all the submersible’s lights off, but perhaps the shrimp’s eye patches were more sensitive.

HOW EYELESS SHRIMP SEE Eyless shrimp live in pitch-black darkness near the hot vents that dot the floor of the mid-Atlantic two miles below the surface. Researchers have discovered that the shrimp use eye patches on their back to see the light emitted by the superheated water and thus avoid getting burned.

The “eyes” are flat patches a quarter-inch long that contain light-sensitive pigments like those found in human eyes.

Eyeless shrimp (Rimicaris Exoculata) length: 2 inches