Challenger Deep - Lifeforms

Lifeforms

The Summary Report of the HMS Challenger expedition lists radiolaria from the two dredged samples taken when the Challenger Deep was first discovered. These (Nassellaria and Spumellaria) were reported in the Report on Radiolaria (1887) written by Ernst Haeckel.

On their 1960 descent, the crew of the Trieste noted that the floor consisted of diatomaceous ooze and reported observing "some type of flatfish, resembling a sole, about 1 foot long and 6 inches across" lying on the seabed.

"... And as we were settling this final fathom, I saw a wonderful thing. Lying on the bottom just beneath us was some type of flatfish, resembling a sole, about 1 foot long and 6 inches across. Even as I saw him, his two round eyes on top of his head spied us — a monster of steel — invading his silent realm. Eyes? Why should he have eyes? Merely to see phosphorescence? The floodlight that bathed him was the first real light ever to enter this hadal realm. Here, in an instant, was the answer that biologists had asked for the decades. Could life exist in the greatest depths of the ocean? It could! And not only that, here apparently, was a true, bony teleost fish, not a primitive ray or elasmobranch. Yes, a highly evolved vertebrate, in time's arrow very close to man himself. Slowly, extremely slowly, this flatfish swam away. Moving along the bottom, partly in the ooze and partly in the water, he disappeared into his night. Slowly too — perhaps everything is slow at the bottom of the sea — Walsh and I shook hands.

Many marine biologists are now skeptical of this supposed sighting, and it is suggested that the creature may instead have been a sea cucumber. The video camera on board the Kaiko probe spotted a sea cucumber, a scale worm and a shrimp at the bottom. At the bottom of the Challenger deep, the Nereus probe spotted one polychaete worm (a multi-legged predator) about an inch long.

An analysis of the sediment samples collected by Kaiko found large numbers of simple organisms at 10,900 m (35,800 ft). While similar lifeforms have been known to exist in shallower ocean trenches (> 7,000 m) and on the abyssal plain, the lifeforms discovered in the Challenger Deep possibly represent taxa distinct from those in shallower ecosystems.

Most of the organisms collected were simple, soft-shelled foraminifera (432 species according to National Geographic), with four of the others representing species of the complex, multi-chambered genera Leptohalysis and Reophax. Eighty-five percent of the specimens were organic, soft-shelled allogromiids, which is unusual compared to samples of sediment-dwelling organisms from other deep-sea environments, where the percentage of organic-walled foraminifera ranges from 5% to 20%. As small organisms with hard, calcareous shells have trouble growing at extreme depths because of the high solubility of calcium carbonate in the pressurized water, scientists theorize that the preponderance of soft-shelled organisms in the Challenger Deep may have resulted from the typical biosphere present when the Challenger Deep was shallower than it is now. Over the course of six to nine million years, as the Challenger Deep grew to its present depth, many of the species present in the sediment died out or were unable to adapt to the increasing water pressure and changing environment. The species that survived the change in depth were the ancestors of the Challenger Deep's current denizens.