Συντάκτης: cretan_adm

Swimming hundreds of feet beneath the ocean’s surface in many parts of the world are prolific architects called giant larvaceans. These zooplankton are not particularly giant themselves (they resemble tadpoles and are about the size of a pinkie finger), but every day, they construct one or more spacious “houses” that can exceed three feet in length.

The houses are transparent mucus structures that encase the creatures inside. Giant larvaceans beat their tails to pump seawater through these structures, which filter tiny bits of dead or drifting organic matter for the animals to eat. When their filters get clogged, the larvaceans abandon ship and construct a new house.

Laden with debris

Laden with debris from the water column, old houses rapidly sink to the seafloor. In a study published in Science Advances on Wednesday, scientists near California’s Monterey Bay have found that, through this process, giant larvaceans can filter all of the bay’s water from about 300 to 1,000 feet deep in less than two weeks, making them the fastest known zooplankton filter feeders.

In doing so, the creatures help transfer carbon that has been removed from the atmosphere.

And given their abundance in other parts of the world, these organisms likely play a crucial role in the global carbon cycle. When it comes to the flow of carbon in the ocean, “we don’t know nearly as much as we should,” said Kakani Katija, a principal engineer at the Monterey Bay Aquarium Research Institute and the study’s lead author.

Carbon in the ocean

“If we really want to understand how the system works, we have to look at all the players involved. Giant larvaceans are one important group we need to learn more about.” In the past, other scientists have tried studying giant larvaceans in the laboratory. But these efforts always failed because the animals’ houses were too fragile to be harvested and collected specimens were never able to build houses outside the ocean.

Zooplankton

To study the zooplankton in their natural habitat, Dr. Katija and her collaborators developed a new deep-sea imaging instrument, called DeepPIV, which they paired with a remotely operated vehicle. DeepPIV projects a sheet of laser light that cuts straight through a larvacean’s mucus house.
A high-definition camera on the remotely operated vehicle can then capture the inner pumping mechanisms illuminated by the laser.

The recording starts with the patter of a summer squall. Later, a drifting tone like that of a not-quite-tuned-in radio station rises and for a while drowns out the patter.

These are the sounds encountered by NASA’s Cassini spacecraft as it dove through the gap between Saturn and its innermost ring on April 26, the first of 22 such encounters before it will plunge into Saturn’s atmosphere in September. What Cassini did not detect were many of the collisions of dust particles hitting the spacecraft as it passed through the plane of the rings. “You can hear a couple of clicks,” said William S. Kurth, a research scientist at the University of Iowa who is the principal investigator for Cassini’s radio and plasma science instrument.

The analysis indicated that the chances of such a collision were slim, but still risky enough that mission managers did not send Cassini here until the mission’s final months. As a better-safe-than-sorry precaution, the spacecraft was pointed with its big radio dish facing forward, like a shield.

The few clicking sounds were generated by dust the size of cigarette smoke particles about a micron, or one-25,000th of an inch, in diameter. To be clear: Cassini did not actually hear any sounds. It is, after all, flying through space where there is no air and thus no vibrating air molecules to convey sound waves. But space is full of radio waves, recorded by Dr. Kurth’s instrument, and those waves, just like the ones bouncing through the Earth’s atmosphere to broadcast the songs of Bruno Mars, Beyoncé and Taylor Swift, can be converted into audible sounds.

Bottom line

Dr. Kurth said the background patter was likely oscillations of charged particles in the upper part of Saturn’s ionosphere where atoms are broken apart by solar and cosmic radiation. The louder tones were almost certainly “whistler mode emissions” when the charged particles oscillate in unison.

Their new technique, described in a study published on Thursday in the journal Science, promises to open new avenues of research into human prehistory and was met with excitement by geneticists and archaeologists.

“It’s a bit like discovering that you can extract gold dust from the air,”

said Adam Siepel, a population geneticist at Cold Spring Harbor Laboratory.
“An absolutely amazing and exciting paper,” added David Reich, a genetics professor at Harvard who focuses on ancient DNA.

DNA from fossil bones

Until recently, the only way to study the genes of ancient humans like the Neanderthals and their cousins, the Denisovans, was to recover DNA from fossil bones. But they are scarce and hard to find, which has greatly limited research into where early humans lived and how widely they ranged.

The only Denisovan bones and teeth that scientists have, for example, come from a single cave in Siberia.

Looking for these genetic signposts in sediment has become possible only in the last few years, with recent developments in technology, including rapid sequencing of DNA. Although DNA sticks to minerals and decayed plants in soil, scientists did not know whether it would ever be possible to fish out gene fragments that were tens of thousands of years old and buried deep among other genetic debris.

Long way

Bits of genes from ancient humans make up just a minute fraction of the DNA floating around in the natural world. But the German scientists, led by Matthias Meyer at the Max Planck Institute for Developmental Biology in Tübingen, have spent years developing methods to find DNA even where it seemed impossibly scarce and degraded.

“There’s been a real revolution in technology invented by this lab,” Dr. Reich said. “Matthias is kind of a wizard in pushing the envelope.”
Scientists began by retrieving DNA from ancient bones:

1. first Neanderthals,
2. then Denisovans.

Suprising findings

To identify the Denisovans, Svante Paabo, a geneticist at the Planck Institute and a co-author of the new paper, had only a child’s pinkie bone to work with. His group surprised the world in 2010 by reporting that it had extracted DNA from the bone, finding that it belonged to a group of humans distinct from both Neanderthals and modern humans. But that sort of analysis is limited by the availability of fossil bones.

“In a lot of cases, you can get bones, but not enough,” said Hendrik Poinar, an evolutionary geneticist at McMaster University. “If you just have one small piece of bone from one site, curators do not want you to grind it up.”