‘Marianas Trench may be a biological hot spot’

An international collaboration of scientists recently led a monthlong expedition to study the deepest point on earth in the Marianas Trench, the Challenger Deep. Researchers found evidence suggesting a trench teeming with life, footage of a new fish species, as well as various samples that may answer questions about deep-sea life in the future, according to the expedition’s co-chief scientist, Dr. Jeff Drazen, in an exclusive interview yesterday.

Researchers aboard the R/V Falkor explored life in what is called the “hadal zone,” which comprises some of the least explored and greatest depths in the ocean. The zone begins at about 6,000 meters and drops down the Challenger Deep, nearly 11,000 meters under the sea.

“The deep sea is generally unexplored,” Drazen said. “We have better maps of the surface of the moon than we do of the bottom of the ocean.”

Trench research can be “very, very challenging,” because of pressure from the distance to the surface of the sea, according to Drazen. For this research, they used landers—platforms that hold sampling equipment like cameras, baited trap, metal grabs, or cores.

Drazen said there were a lot of custom-made titanium housing and customized cameras and sensors, as well as “the first very deep oxygen sensors in the world” on some of their gear.

The engineering, according to Drazen, helped researchers sample the hadal life that they discovered was “fascinating and rich.”

“I think some of the mistakes some scientists have made in the past is they have charged to the deepest part of the trenches. There’s actually not as much there as in many other places,” he said, recalling director James Cameron’s 2012 expedition in the trench where Cameron drove straight down the Challenger Deep for 20 or 30 minutes, and eventually described it as a “monotonous plain of mud,” according to Drazen.

“We took a very different approach. We sampled the sides of the trenches. That’s where all the action is. …The camera systems saw boulder fields, and some crazy Dr. Seuss-like sponges, and a really diverse array and abundant groups of fishes.”

Ethereal fish

The researchers also discovered a new species of snailfish.

“You can see right through the body,” Drazen said of the snailfish. “You can see their liver, their bones.”

In their discovery, researchers broke the deepest record of fish several times; the first time at 7,900 meters, the last at 8,143 meters.

They recorded the fish accidentally, according to Drazen, through a task camera intended to check on the functionality of equipment.

Technicians first saw the fish, he said, and called the fish biologists over.

“We sat down and they played it for us. And as it swam into the field of view, we just were totally surprised. Not that there was fish, but just at what it was. It looked so different than any other fish that we knew of in the hadal zone, or anywhere else in the deep sea.”

“We knew it was a new species immediately,” he added. Footage of the “ethereal” and ghost-like snailfish can be viewed online.

Scientists looked for the fish as far as 8,300 meters but did not observe them there, according to Drazen. The furthest they saw the fish was at 8,143 meters, he said, and none were found at 8,200 m.

This, according to Drazen, lined up with the hypothesis of another scientist on board which basically said that no fish live beyond 8,400 meters deep as they are not molecularly suited to survive those deep pressures.

Researchers were able to catch several dozens of the shallower snailfish species but not of the deeper, newly discovered one. From what they have, scientists will study the fish to see what they eat, and how old they are.

Drazen said they would know more in the coming months.

‘Giant beach fleas’

Scientists also caught giant amphipods—as large as 30 cm—that to average beachgoers may look like beach flies, according to Drazen.

They deployed 30 baited traps that also caught fish and shrimp, he said.

The samples revealed a surprising discovery about the physiology of the amphipods, as they were composed mostly of liquid, according to Drazen.

“We opened them up and it was all liquid inside. It was like they were hollow. We had to scrounge to find little bits of muscle. There is almost nothing in them. We’re still trying to find out why that is. We’re not entirely sure.”

Right now, their leading hypothesis is that these arthropods have evolved to become significantly large so that predators would not eat them, according to Drazen.

“One adaption to become very successful in this kind of environment, we think, is you become very large so you can’t fit in these predators’ mouths any longer. But you don’t want to just get big and pay all the energetic costs of growing large. So we think they build their skeleton up and they don’t put very much inside of it,” he said.

The secondary advantage of this adaptation is that amphipods can “gorge” themselves if they find dead fish on the seafloor, Drazen said.

“If we actually caught some of these amphipods that had been feeding on bait for hours and hours on end, my guess is that they would have a gigantic gut just full of bait.”

Muscles were found along their skeleton shell, a digestive tract and stomach near the center, and a nerve network and brain around the head of the animal, according to Drazen.

But he emphasized that more detailed study must be done.

“I don’t know what [the inner fluid] is composed of,” he said.

Teeming with life

Scientists also measured the activity of the mud in the deepsea floor. They did this through measuring how fast sediment organisms breathed, or how fast they used oxygen.

Researchers discovered that the rate at which the mud communities were using oxygen was similar to organisms at shallow depths near the surface, according to Drazen.

He said the rates were “way higher than anything measured in other parts of the deep sea,” and more similar “to what you find off the Mississippi River delta.”

Drazen said the trench can acts as a “funnel” for detritus that comes from the surface, because of how the trench is shaped, and how sediments often slide downs from its sides.

This has led researchers to think that the trench is a “biological hotspot.”

“That’s not what you usually you find in the deep sea. The farther you get from the surface of the ocean, the less food there is. We think the [Mariana] Trench is very unique. There actually may be more food the deeper you go in the Trench,” he said.

He added that he could speak more definitely on the matter once more analysis is done. Extensive study would probably begin early next year, he said, with updates possibly available around the middle of the year.