The fastest claws in the sea belong to the young snapping shrimp

For some time now, mature shrimps have the fastest claws under the waves. But it turns out they are nothing compared to their kids.

Juvenile shrimp snapping produce the highest known underwater accelerations of any reusable body part, researchers report on February 28 in Journal of Experimental Biology. While the speed of the claws is not very impressive, they go from zero to full throttle in record time.

To scare off predators or competitors, the shrimp create a sounding wave by striking it with its strong claws. The shrimp store energy in the exoskeleton by bending the claws open, setting it in place like a bow and arrow mechanism, says Jacob Harrison, a biologist at Georgia Tech in Atlanta.

Burning the nail and releasing the elastic energy produces a high velocity water jet. Bubbles form behind her and immediately implode, releasing a huge force of energy, momentarily flashing like the sun and creating a crackling noise (SN: 10/3/01).

But it is unclear how early in life a shrimp might use this weapon. “We know that the sounding shrimp has done this in a really serious way,” says Harrison. “But we really know nothing about how this machine was developed.”

While a graduate student at Duke University, Harrison and his advisor, biomechanist Sheila Patek, raised a bigclaw snapping shrimp (Alpheus heterochaelis) from the eggs in the factory. At 1 month, the tiny shrimp — less than a centimeter long — began to burn disturbed claws. The researchers captured high-speed video footage of these tornadoes and calculated their speed.

The shrimp was just able to create sliding bubbles like the adults. Although they are one-tenth the size of adults, juvenile claws accelerate more or less quickly. This acceleration – about 600 kilometers per second – is in “the same order of magnitude as a 9 millimeter gun bullet left behind,” Harrison says.

Dracula the Ant (The mystery of the camel) and some termites make more explosive blows but do not drive against water. The stinging jelly cells launch their poisonous harpoons about 100 times faster, but the mechanism for their use is unique. A shrimp, on the other hand, can burn its claws repeatedly.

The juvenile firing and bubble creation were not very reliable at the smallest sizes, but the shrimp tended to break any effort. The team wondered if the young shrimp could exercise and form the necessary musculature.

If so, that training would ultimately be crucial to the claws’ function, says Kate Feller, a visual ecologist at Union College in Schenectady, NY, who similarly studies the ultrafast mantis shrimp and was not involved in the new study. “If you somehow manipulate the claws so that they can’t close or break,” he wonders, “how would these mechanisms affect their ability to unfold?”

Understanding the storage of elastic energy in biological materials and how it flows through them is “tricky,” Harrison says. Figuring out how tiny hooves can generate so much energy without breaking can help researchers explain this superpower.