The ultimate high-pressure job: surviving on the seabed

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A RICH menagerie of animal life has been discovered on the deepest seabed in the world where the pressure is a crushing 16,000lbs per square inch.

A team of Japanese and British marine biologists found delicate, soft- walled creatures dominate the microbial life-forms that inhabit the sediment at the bottom of a deepwater trench in the Pacific. The trench, called Challenger Deep, lies 400 miles off the Marianas Islands in the south Pacific. At its deepest, the trench is seven miles below the waves and would comfortably submerge Mount Everest in a mile-deep layer of water.

Yuko Todo, of Shizuoka University in Japan, and Andrew Gooday, of the Southampton Oceanography Centre, recovered the deep-sea microbes using a robot submersible called Kaiko which operates in severe high pressure.

"Extreme depths make it very difficult to sample the bottom of deep-ocean trenches," the scientists say in the journal Science. "As a result, almost nothing is known about small, sediment-dwelling organisms - meiofauna - in these environments, which are among the most remote on Earth."

The Kaiko submersible collected sediment samples that yielded 432 types of microbial plankton called foraminifera. All but four of these microbes were soft-walled and delicate.

The Challenger Deep has formed over six million to nine million years by tectonic plates grinding over each other, one being pulled underneath in a subduction zone. The scientists believe the plankton life has evolved from other deep-ocean microbes that gradually became acclimatised to deeper and deeper seabeds.

"Its distinctive foraminiferal fauna probably represent the remnants of an abyssal assemblage that was able to adapt to the steady increase in hydrostatic pressure over this period," the scientists say.