The physics of the pop
In the coral reefs of the Caribbean, a creature measuring only 3-5 centimeters long produces one of the loudest sounds in the ocean. Members of the Alpheidae family, commonly known as pistol or snapping shrimp, possess one oversized claw that is a high-speed weapon. This claw, which can be larger than half the shrimp's body, has a two-part structure. A mobile "hammer" section pulls back and locks into place, and when released, it snaps shut with incredible speed.
The resulting motion fires a jet of water at speeds up to 100 kilometers per hour (about 62 mph). This rapid water movement is governed by Bernoulli's principle; the high velocity causes the local pressure to drop dramatically, forming a low-pressure vapor-filled bubble in the water. This process is known as cavitation. The entire event, from the claw snap to the bubble's collapse, occurs in under a millisecond. The sound itself doesn't come from the two parts of the claw hitting each other, but from the violent collapse of this cavitation bubble.
A star in a bubble
The collapse of the cavitation bubble is an extreme event. As the surrounding higher-pressure water rushes in to crush the vapor-filled space, the contents are compressed catastrophically. For a fraction of a second, the temperature inside the collapsing bubble soars to over 4,700°C (around 8,500°F). This is nearly as hot as the surface of the sun.
This intense heat causes the bubble to emit a brief, intense flash of light, The phenomenon is called sonoluminescence. While the light is too dim and short-lived, lasting less than 10 nanoseconds, to be seen by the naked eye, it marks the first discovery of an animal producing light through this effect. The primary weapon is not the heat or light but the powerful acoustic shockwave generated by the bubble's collapse. This pressure wave can reach 218 decibels, louder than a gunshot, and creates an acoustic pressure of 80 kPa at a distance of 4 centimeters. This force stuns or kill the small fish and crabs the shrimp preys upon.