Shrimp link to vent life

The larval habits of a bizarre blind shrimp that lives 3,000 feet below the surface of the sea may provide the only link between life around volcanoes on the ocean floor, known as hydrothermal vents, and the rest of life on Earth.

Organisms living near these vents depend on chemical energy gushing from the vent and were thought to be completely isolated from the sun's energy on which all other life depends.

The type of fat in the bodies of shrimps provides clues about their diet and scientists at Plymouth Marine Laboratory have discovered that larval shrimps are plugged in to food chains in the surrounding ocean - providing the only known link to the outside world.

Scientists spent last summer fishing shrimps at a hydrothermal vent in the Mid-Atlantic Ridge where this creature dominates the animal life. Called "blind" because, instead of conventional insect-like eyes, they have a thin layer of cells on their back which may be sensitive to infra-red light, shrimps store fat as lipids to fuel their movements.

"Lipids in the adult shrimps have a very distinctive chemical signature," said David Dixon, a marine biologist at Plymouth. "Like all other animals here they feed on bacteria which in turn depend on the chemical energy, mainly heat and hydrogen sulphide, emerging from the vent."

Lipids from the larval shrimps told a different dietary story - they contained fats that had come from feeding on plankton (microscopic oceanic organisms, the plant forms of which harness sunlight to manufacture food).

"The larval shrimps must be plugged in to oceanic systems that depend on sunlight," said Dr Dixon. "Life at the vent is not as isolated as we had thought."

Hydrothermal vents are not permanent but wax and wane with changes in volcanic activity. Vent species, which frequently face extinction, must be able to colonise newly formed vents as old ones die.

Because the adult forms are unable to move far they invest huge amounts of energy in producing millions of young that can travel great distances on the ocean currents in search of new vents.

"Larval blind shrimps not only provide a link to other vents but also to other worlds," said Dr Dixon.