Pistol shrimp, or snapping shrimp, are a family of shrimp known for their asymmetrical claws and their ability to create shockwaves with their bigger claw.
There are hundreds of species, the majority of which live in tropical and temperate coastal and marine waters.
These guys are so loud that they can interfere with sonars and other means of underwater communication.
Biology
Pistol shrimp grow to just about 5 cm. They’re tiny.
It’s large claw can be half of the size of its body.
The Pistol
Unlike most shrimp, pistol shrimp don’t have pincers don’t have pincers at the end of their claw. Instead, they have a hammer-like mechanism.
It’s basically like a hammer and anvil. The anvil, called a propous, never moves. The hammer, called the dactyl, part moves backwards about 90 degrees.
At the same time as one muscle pulls the dactyl away from the propous, another muscle pulls it towards the propous. This creates tension.
It’s like a tug of war, if one side lets go the other will fly backwards much faster than if it they were moving backwards on their own.
Then a second muscle pulls the dactyl into the propous. All that potential energy gets released at enormous speeds. The movement and the impact displace water extremely fast. This is a jet stream. It can be as fast as 115 km/h.
The jet stream creates areas of low pressure, lower than the vapour pressure of water. There are little bubbles in the water and when they find a low pressure system they expand rapidly. This is called cavitation.
The big bubble is surrounded then by regular pressure water which compresses it and makes it implode.
This implosion, rather than the impact of the propous and dactyl is what makes the popping sound.
As a side note, snapping shrimp have little hairs on their snapping claw and they use those to feel jets streams from other shrimps snapping. This is used for communication.
Back to the good stuff, the implosion of the bubble creates gigantic amounts of energy. It can briefly get as hot hotter than 4000 degrees celsius. For scale, lava is about 1000C. The temperature of the surface of the sun is 5500C.
The weirdest thing that happens is sonoluminescence. When a bubble collapses it emits light. And nobody knows why, not even Rick and Morty fans.
The shockwave this event creates is enough to kill and dismember their prey. It’s like being a shot with a missile that doesn’t explode.
Some species even use this to make burrows in rocks.
Quick Facts
Pistol shrimps that live in coral reefs often have symbiotic relationships with goby fish.
They’re roommates. The shrimp will make and maintain a burrow to share with the fish and the fish will be the lookout, always scanning the seas for danger.
When both of them are outside the burrow, the shrimp will hold the fish’s tail with its antenna. The fish has better vision and if it sees something sketchy it wiggles its tail, which means they should go back in.
There’s a species of pistol shrimp from Australia that lives in eusocial societies (like ants and bees).
Synalpheus Regalia is very strange because eusociality is usually only found in insects and in the naked mole rat.
They live in sponges, in colonies of over 300 individuals, centered around a queen.
They help raise all the young and protect the colony from outsiders.
Because these guys usually live in big groups, and they’re snapping all the time for hunting and communication, they’re one of the loudest and most noticeable animals in the ocean.
At the source, the snaps can reach up to 210 decibels.
A chainsaw is about 120 decibels, which is coincidentally that same amount where it will cause pain to hear it.
A jet engine is about 140db.
This noise can be heard day and night and it has been described as the sound of burning twigs.
It’s so loud and widespread that interferes with sonars. They create something called “acoustic screens”. The US used them to enter Japanese waters undetected during WW2.
