"If this announcement promotes greater interest in these deepwater [life-forms], then it has done a good job," he said. "I find it all very interesting, largely because of the unresolved questions it raises. And that is how science is supposed to work."
An earlier DNA analysis of similar forms suggests to Kitazato and colleagues that the Challenger Deep foraminifera may resemble some of the first life-forms on Earth.
The newfound specimens are primitive organisms that may be part of a lineage that is thought to date back to Precambrian times. The Precambrian is the earliest era in Earth's history. It came to an end some 542 million years ago, when shelled organisms first appeared in the seas.
But the University of California's Lipps is not so sure just how primitive the new specimens are. He said that DNA analysis of similar foraminifera is needed before conclusions are drawn.
Most surprising to Kitazato and his colleagues is the high percentage of tube-shaped, soft-walled foraminifera at Challenger Deep. They account for 85 percent of the assemblage. In most deep-sea environments, they make up 5 to 20 percent of the living assemblage. The rest of the assemblage was made up of spherical and clumped-together forms.
Hard-shell species are unable to survive at such depths, the researchers note in Science.
Though Kitazato and colleagues thought some life would exist at Challenger Deep, the abundance caught them off guard. Kitazato said there are likely two reasons for the abundance.
First, soft-walled foraminifera house waste pellets that the scientists believe may be a source of nutrients in the otherwise nutrient-poor environment. "Second is that Challenger Deep is scarce in predators for foraminifera, [allowing] soft-shelled foraminifera to live safely," Kitazato said.
The foraminifera found at Challenger Deep are most closely related to forms that live at an average depth of 16,400 feet (5,000 meters). Kitazato and his colleagues theorize that these forms adapted to the steady increases in pressure as the Challenger Deep formed and deepened over the last six to nine million years.
As the depth increased, hard-shelled foraminifera would have been weeded out, as they are unable to survive at great depth, Kitazato said.
But according to Lipps, the foraminifera's adaptations to the deep sea may have taken place before the Challenger Deep formed. "[Groups of life-forms] move around a lot in the ocean, especially over the geologic ages, so this might be an even more reasonable speculation," he said.
Scientists say that foraminifera are of crucial importance to ocean biology and geology. Among creatures found in the deep sea, they make up more than half of all living matter and fill the lower part the food chain.
In general, foraminifera are useful for reconstructing past environments, studying ancient climate change, and dating sediments, the Smithsonian Institution's Huber said. But the Challenger Deep foraminifera are of little help in these efforts.
"However, they are certainly one more example of how foraminifera have adapted to occur in a huge range of environments," he said.
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