Pistol shrimp are unique members of the shrimp family. They come equipped with a special single oversized claw which can be used like a sonic weapon, producing a burst of sound which is actually capable of killing small marine animals. Although pistol shrimp are small, they are responsible for a surprising amount of the noise in the ocean, and the snapping of pistol shrimp has even been known to disrupt the navigation equipment on submarines.
Formally, pistol shrimp are known as Alpheidae, the name for the broad family which encompasses hundreds of species of pistol shrimps. Some biologists prefer to the term Alpheid shrimp, in a reference to the family. Like other shrimp, pistol shrimp are crustaceans, with an assortment of legs and claws used for navigation and manipulating prey. The claws of a pistol shrimp are distinctive because they are symmetrical: one arm is much bigger than the other. Intriguingly, if the snapping arm of a pistol shrimp is disabled or amputated, the other claw will grow in size to replace it.
The Alpheid family is quite large, and as a result species of snapping shrimp are found all over the world. The creatures tend to live in burrows, and are often found in coral reefs, undersea grass mats, and oyster flats. In some cases, pistol shrimp may form symbiotic relationships with other creatures such as sponges or goby fishes. Some even live in freshwater, demonstrating the immense biological diversity which can be found in a single family.
Originally, biologists thought that the snapping sound of pistol shrimp was caused by clicking the claws of the snapping arm. However, the sound is actually caused by a cavitation bubble. When a pistol shrimp snaps its claw, it sends out a high speed jet of water which creates turbulence, resulting in the formation of low pressure bubbles. When the high pressure of the ocean pops the bubbles, they emit a sharp “crack” just like a pistol.
It also appears that the bubbles emit a brief flash of light when they collapse. This is because the bubbles compress so quickly that the air inside cannot escape. As a result, it becomes superheated, sometimes approaching the surface temperature of the sun. The flash of light is referred to as “sonoluminesence,” and it appears to be unique to pistol shrimp, as biologists have not observed a similar phenomenon in connection with other animals.
Although pistol shrimp are not much of a threat to people, they pack a serious punch for such small creatures!