Pistol Crabs: The Gunslingers of the Seas


EStrange cracking and crackling can be heard when pistol shrimp cavort in coral reefs, seagrass meadows or other shallow water biotopes. The little animals rightly bear their name: In the form of the larger of their two scissors, they actually have a kind of water pistol: With a special mechanism, they can close these scissors in a flash. The negative pressure in the water jet that shoots out becomes so great that an air bubble is created. This cavitation bubble then immediately implodes again with a loud bang. The crabs are less concerned with this bang effect than with the resulting pressure wave: the pistol shrimp use this to incapacitate their prey.

Smaller than a brown crab

A maximum of five centimeters long Alpheus heterochaelis, also known as the cracker shrimp – and thus smaller than the North Sea shrimp, which is known in this country as a crab. Of the more than 600 different pistol shrimps that populate coastal areas, especially in the tropics and subtropics, this species, which is distributed from North Carolina to Brazil, is the largest. It can shoot with corresponding power - and it does: off the east coast of America, the animals duel with their own kind in order to vigorously defend their territory and their shelter. Disputes of this kind are the order of the day.

This leads to unfortunate consequences. Because what the pressure wave generated by the banger shrimp does to the nervous system in particular is shown by the prey hit: worms, but also small crabs and fish are immediately stunned by the shots, if not fatally injured.

The pistol shrimp Synalpheus pinkfloydi was named after the rock band Pink Floyd.  With his large scissors, he creates a pressure wave, resulting in a loud bang.


The pistol shrimp Synalpheus pinkfloydi was named after the rock band Pink Floyd. With his large scissors, he creates a pressure wave, resulting in a loud bang.
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Image: Arthur Anker/Universidade Federal de Goiás Brazil/dpa


Visor in head armor protects against brain trauma

But in a duel with conspecifics, firecrackers don't seem to be harmed, even if one fires his shot just a centimeter in front of the other's head. Apparently, a visor integrated into the head armor saves the banger from an imminent brain trauma. This is reported by biologists led by Alexandra Kingston from the University of Tulsa, Oklahoma, and Sarah Woodin from the University of South Carolina in Columbia in the journal "Current Biology".



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