Deepest waters in sea have plankton

WASHINGTON — Tiny, single-celled organisms, many previously unknown, have been discovered beneath nearly seven miles of water in the deepest part of the ocean.

A sample of sediment collected from the Challenger Deep southwest of Guam in the Pacific Ocean yielded several hundred foraminifera, a type of plankton usually abundant near the ocean surface.

"On the species level, all the species we found from the Challenger Deep are quite new," researcher Hiroshi Kitazato said vie e-mail.

The outer shapes are similar to other known foraminifera, but details of their structure differ, said Kitazato, of the Institute for Research on Earth Evolution, Japan Agency for Marine-Earth Science and Technology.

"I am very surprised that so many very simple, soft-shelled foraminifera are dwelling at the deepest point of the world ocean," he added.

"It is also exciting that most of the group belong to the oldest branch of foraminifera," he added, suggesting that these deep locations may form some sort of refuge.

These distinct creatures probably represent the remnants of a deep-dwelling group that was able to adapt to the high pressures, researchers suggest in a report in this week's issue of the journal Science.

Because the water is so deep, the pressure where the find was made is 1,100 times more than normal atmospheric pressure at the surface.

While many foraminifera have hard shells, researchers noted that this newly found group does not.

Similar, though not identical groups have been found in other, slightly shallower ocean trenches, they note.

The creatures probably can exist by ingesting particles of organic matter that drift from above or materials that are dissolved in the seawater, Kitazato said.

The research was funded by the Japan Agency for Marine-Earth Science and Technology, the Japan Society for Promotion of Science, the Kaplan Foundation and the Natural Environment Research Council.