Baby starfish scoop up food by spinning miniature whirlpools. These vortices catch algae and draw them close so the larva can slurp them up, researchers, including Dr. William Gilpin et al from Stanford University report in Nature Physics (12/19/16).
Before starfish, which are not fish but echinoderms, take on their familiar shape, they freely swim ocean waters as millimeter-sized larvae.
To swim around on the hunt for food, the larvae paddle the water with hair-like appendages called cilia.
Starfish larvae also adjust the orientation of these cilia to fine-tune their food-grabbing vortices.
Researchers studied larvae of the bat star (Patiria miniata), a starfish found on the U.S. Pacific coast,
by observing their activities in seawater suffused with tiny beads that traced the flow of liquid. (Does this remind you a bit of Obi, the parrotlet, and observing the air around him that was suffused with aerosol droplets as he flew?)
Too many swirls can slow a larva down, the scientists found, so the baby starfish adapts to the task at hand, creating fewer vortices while swimming and whipping up more of them when stopping to feed.
A video of the experiment is linked here.
And I thought we were supposed to wait an hour after eating before swimming. . .
A post on starfish the week we lost two stars, Carrie Fisher and her mom, Debbie Reynolds? Twin stars/spirits, born of an instant. Rest easy together, ladies.
Starrily,
Steph
My artist friend, Judith's, words to Don T. on a clay tablet:
An unusual noise that was recorded near the Mariana Trench could be a never-before-heard whale call.
Called the "Western Pacific Biotwang," this newly discovered call might be from a minke whale, a type of baleen whale, according to the researchers who documented the vocalization. A baleen whale has plates of whalebone in the mouth for straining plankton from the water.

The Mariana Trench stretches 1,500 mi (2500 km) in an arc that is edged by the islands of Guam and Saipan. Its deepest point is known as the Challenger Deep, some 35,756 feet (10,890 m) — or nearly 7 miles (11 km) — beneath the surface of the sea. The trench is deeper than Mount Everest is tall.
Lasting between 2.5 and 3.5 seconds, the five-part call includes deep moans at frequencies as low as 38 hertz and a metallic finale that pulses as high as 8,000 hertz.

“It’s very distinct, with all these crazy parts,” said Dr. Sharon Nieukirk, senior faculty research assistant in marine bioacoustics at Oregon State U.“The low-frequency moaning part is typical of baleen whales, and it’s that kind of twangy sound that makes it unique. We don’t find many new baleen whale calls.”
Recorded via passive acoustic ocean gliders, which are instruments that can travel autonomously for months at a time and dive up to 1,000 meters, the Western Pacific Biotwang most closely resembles the so-called “Star Wars” sound produced by dwarf minke whales on the Great Barrier Reef off the northeast coast of Australia, researchers say.
This article describes a recording of the new Western Pacific Biotwang. You may hear the 1 minute Biotwang here.
"We don't really know that much about minke whale distribution at low latitudes," Dr. Nieukirk said. "The species is the smallest of the baleen whales, doesn't spend much time at the surface, has an inconspicuous blow, and often lives in areas where high seas make sighting difficult. But they call frequently, making them good candidates for acoustic studies."
"The call still needs to be translated. Most baleen whales use specific vocalizations for seasonal breeding and feeding, but this call — since it seems to occur all year — may have a complex function," the researchers said.
Biotwang, Biotwang, Biotwang--what a fun word to say!
Steph
O
ceanic crust created by the earth today is significantly thinner than crust made 170 million years ago during the time of supercontinent Pangaea, according to U. of Texas, Austin, scientists. The Earth's crust under the oceans is up to 1 mile thinner today than it was during that Pangaean time.

"The thinning is related to the cooling of earth's interior prompted by the splitting of Pangaea, which broke up into the continents that we have today," said Dr. Harm Van Avendonk, the lead author of the study. The research published in Nature Geosciences on December 12, 2016, illuminates how plate tectonics has influenced the cooling of the Earth's mantle throughout geologic history.
"What we think is happening is that the supercontinent was like an insulating blanket," Van Avendonk said. "So when these continents started opening up and the deeper mantle was exposed, more or less, to the atmosphere and the ocean it started cooling much faster."
The mantle is the very hot, but mostly solid, layer of rock between the Earth's crust and core. Magma from the mantle forms oceanic crust when it rises from the mantle to the surface at spreading centers and cools into the rock that forms the very bottom of the seafloor.
Since about 2.5 billion years ago, the mantle has been cooling, a phenomenon that does not influence the climate on the surface of the Earth and has nothing to do with the issue of short-term human-made climate change (which is a real phenomenon, DT!). This study suggests that since the breakup of Pangaea, the cooling rate of the mantle has increased from 6 - 11 degrees Celsius per 100 million years to 15 - 20 degrees per 100 million years. Since cooler mantle temperatures generally produce less magma, it is a trend that's making modern day ocean crust thinner. The illustration below of a slice of earth ties in well with the pizza analogy ;-).
"It's important to note the Earth seems to be cooling a lot faster now than it has been over its lifetime," Dr. Van Avendonk said. "The current state of the Earth, where we have a lot of plate tectonic events, this allows the Earth to cool much more efficiently than it did in the past."
The research that led to the connection between the splitting of the supercontinent and crust thickness started when Dr. Van Avendock and Ph.D. student Jennifer Harding, a co-author, noticed an unexpected trend when studying existing data from young and old seafloor. They analyzed 234 measurements of crustal thickness from around the world and found that, on a global scale, the oldest ocean crust examined, Jurassic in age, is 1 mile thicker, as noted above. The oldest oceanic crust (or sima, short for silica and magnesium, mainly basalt) is Jurassic in age due to the "recycling" nature of this denser crust versus less dense continental crust (or sial, short for silica and aluminum).
The link between crust thickness and age prompted two possible explanations, both related to the fact that hotter mantle tends to make more magma. (1) Mantle hot spots, highly volcanic regions, such as the Hawaiian Islands and Iceland, could have thickened the old crust by covering it in layers of lava at a later time. Or, (2) the mantle was hotter in the Jurassic than it is now.
The analysis ruled out the hot spot theory; thick layers of old crust formed just as easily at distances greater than 600 miles from hotspots, a distance that the researchers judged was outside the influence of the hotspots. In contrast, the analysis supported the hypothesis of mantle cooling after the breakup of the supercontinent.

The discovery that breaking up Pangaea cooled the mantle is important because it gives a more nuanced view of the mantle temperature that influences tectonics on earth. The researchers also note that the study illustrates the success that can come from spontaneous collaboration and leveraging basic research on a global scale.
Coolly and Warmly,
Steph


A parrotlet named Obi has his own set of custom-made safety goggles (made from human-sized ones) to protect his eyes when he flies through a laser sheet, as he has been trained to do. Researchers at Stanford University are studying how air moves in the wake of Obi's flight.
This 46-second video of Obi's flight shows the vortices swirling around the bird's flightpath, thanks to the lasers he is flying through.
Researchers at Stanford University are studying how the air moves in the wake of a bird's flight. Thank to Obi, along with graduate students Eric Gutierrez and Diana Chin, and mechanical engineer David Letink, we now know that there may be some faults in many flight models.
"The goal of our study was to compare very commonly used models in the literature to figure out how much lift a bird, or other flying animal, generates based off its wake," Chin said. "What we found was that all three models we tried out were very inaccurate because they make assumptions that aren't necessarily true."
To test the models, the team trained Obi, a parrotlet or pocket parrot, to wear the goggles and fly from one perch to another. Then a laser sheet was seeded with non-toxic, aerosol-sized particles. As Obi flew through this laser sheet, the disturbed particles swirled into vortices left in his wake.
The tests showed something unexpected. Computer models predicted that once the whirling air patterns or vortices were created by a bird's wings, they would remain relatively stable in the air. But the patterns Obi traced began to disintegrate after the bird flapped its wings just a few times.
"We were surprised to find the vortices that are usually drawn in papers and text books as beautiful doughnut rings turned out to break up dramatically after two to three wing beats," Lentink said. He explained that this meant the models, which are widely used in animal flight studies to calculate an animal's lift based on the wake it produced, were likely inaccurate.

"Whereas vortex breakup happens far away behind the aircraft (more than a thousand meters) in birds, it can happen very close to the bird, within two or three wingbeats , and it is much more violent," said Letink.
The team also found that the models they tested did not accurately predict the lift generated by Obi's wings. This research joins other studies conducted by the lab on many different animals, including different bird species, bats, and insects. The team hopes the findings can be used to help develop flying robots or drones that flap wings, rather than rely on rotors.
Wonder if Obi knows Obi-wan Kenobi,
Steph
