Biologists have discovered an uncomfortable truth. The shrimps living in the darkness of the ocean floor were literally blinded by science, they reveal today in Nature magazine.
Rimicaris exoculata and mirocaris fortunata are two species of crustacean that dwell in the Mid-Atlantic Ridge, in the deepest part of the ocean, where conditions are so dark and detached from the rest of the planet nobody imagined that they would exist at all. Oceanographers using submersibles discovered that the ridge was home to astonishing forms of life. Far from the sun, whole communities of creatures gained nutrients, warmth and energy from submarine volcanic vents.
The discovery made history. It also made the shrimps blind, according to Dr Peter Herring of the Southampton oceanography centre and two zoologists at Leicester university, Dr Peter Shelton and Dr Edward Gaten.
They examined shrimps which had been captured by floodlight and brought to the surface.
"We found the shrimps do not have a retina. It seems to have degenerated. This structural change looks exactly like what we find in shallow water shrimp which we know suffer light damage," Dr Herring said. The shrimps had sophisticated "thoracic" eyes - literally eyes in the back of the head. But by the time they came to the surface, they could not see much.
Since they were brought up in light-proof boxes, the damage must have been done the first time a submersible floodlit the darkness of their world.
The eyes are a puzzle: experiments with scampi (which also live in the dark) have shown that crustaceans thrown back into the water, blinded, seem to survive perfectly well.
Since there is no light, the guess is that the shrimps use their thoracic eyes as infra-red detectors, sensing columns of hot volcanic water in the ultra-cold of the ocean bottom. Nobody can begin to guess how many shrimps there are - but the implication is that every one visited has been blinded. "A well-visited site could have quite a large number of animals whose sight has been damaged," said Dr Shelton. "We have no evidence that it affects their behaviour at all. But I think people should just be aware of it as they study the behaviour of these animals."