Science

This is why pistol shrimp are immune to their powerful shock waves

in great shape , A translucent “helmet” on the bigclaw that bites off the shrimp’s head protects its brain from the shock waves generated by its claw-snapping.

Kingston et al., Current Biology

The small-but-mighty pistol shrimp can snap its claws with enough force to produce a shock wave to stun its prey. So how does the shrimp appear immune to its sonic weapon? Scientists have concluded that the shrimp are protected by a small clear helmet that protects the organism from any significant nerve damage by dampening shock waves, according to a paper recently published in the journal Current Biology.

The snapping shrimp, aka pistol shrimp, is one of the tallest creatures in the ocean, along with sperm whales and beluga whales. When enough of these shrimps snap in at once, the noise can dominate the soundscape of the coastal ocean, sometimes confusing sonar instruments. Source of that photo: An impressive set of oddly shaped claws; The bigger of the two produces the snap. As I wrote at Gizmodo in 2015:

Each snapping sound produces a powerful shock wave with enough oomph To stun or kill a small fish (the typical prey of shrimp)… that shock wave in turn produces collapsing bubbles that emit a barely visible flash of light. It’s a rare natural example of a phenomenon called sonoluminescence: Zap a liquid with sound, create some bubbles, and when those bubbles collapse (like bubbles inevitably do), you get a burst of light. I guess you could call it “shrimpoluminescence”.

Scientists believe that snapping is used for communication as well as hunting. A shrimp on the prowl will hide in a bill or similar inconspicuous spot, extending the antennae to detect any passing fish. When this happens, the shrimp emerges from its hiding place, pulls its claws back, and breaks loose with a powerful snap, producing a deadly shock wave. It can then pull the stunned prey back into the burrow to feed.

Hear the crackling sounds of the pistol shrimp snapping. Credits: AGU.

In 2020, scientists at the Woods Hole Oceanographic Institution announced the results of their experiments with pistol shrimp in tanks in the laboratory, as well as listening to shrimp in the ocean at different water temperatures. They concluded that as ocean temperatures increase with climate change, snapping prawns will blink more frequently and louder than previously thought. This is because shrimp are essentially cold-blooded animals, so their body temperature and activity level will respond to changes in their environment. This will make the global ocean soundscape even more noisy.

Alexandra Kingston of the University of Tulsa in Oklahoma and her co-authors on this latest paper were curious as to how pistol shrimp can survive the powerful shock waves generated by their claws, which can cause both short-term and long-term damage to nerve tissue. could. Specific. The shrimp must have protective mechanisms, and the team thought the creature’s translucent orbital hood—a helmet-like extension of its exoskeleton that covers the eyes and brain—could be the key. Many species of snapping shrimp have such hoods, but other crustaceans do not.

so kingston and others, devised a series of asylum-seeking behavioral experiments to test this hypothesis. He divided his laboratory pistol shrimp into four groups. They surgically removed the orbital hoods of those two groups and retained the hoods in the other two groups. Snapping shrimp usually retreat into a comfortable burrow when they feel threatened or find themselves in an unfamiliar area. Since the shock waves generated by the snap can damage the brain, without the protective hood it must take longer for the shrimp to find its way into a burrow.

In tests, a group of hooded shrimp and a hooded group were exposed to three snap-induced shock waves; As a control, a second hoodless group and a second hooded group were not subject to shock waves. All four groups of shrimp were then released into one end of the experimental arena, and the team timed how long it took for each shrimp to find its way back to the other end.

Result: Hoodless prawns exposed to shock waves reacted quickly to shocks, by jerking, turning around, or even falling, whereas intact shrimp did not react at all to snaps. These hoodless shrimp also took seven times longer to make their way to the burrow than the other three groups, and showed signs of disorientation and difficulty controlling their limbs.

What makes Orbital Hoods such an effective dampener? There is an opening at the front end of the hood, and a layer of water between the inner surface of the hood and the surface of the shrimp eyes. “We propose that when a shock wave strikes an orbital hood, a rapid change in pressure causes the water beneath it to be expelled through the anterior opening, away from the shrimp’s head, The authors wrote. “Through the removal of water, some of the kinetic energy of the shock wave can be redirected and released.”

Subsequent experiments proved this. The orbital hood of the pistol shrimp forms “the first biological shell system known to have such a function,” the authors wrote. quintal and others, Looks like their findings could help design more efficient protective headgear for military personnel or others working with explosives and other powerful shock waves.

“It’s really hard to stop these pressure waves,” Kingston told New Scientist. “Even things like conventional Kevlar armor don’t stop these shock waves. They can travel through that material. My group is certainly going to be a part of material scientists and engineers, and probably in the future the military.” hoping to work with, so that trying to do something that would be more effective than just protecting against secondary [physical] Explosion injuries.”

DOI: Current Biology, 2022. 10.1016/j.cub.2022.06.042 (about DOI).

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