When the tide is out, a staccato of sharp pops resounds from creek beds and pools backed up behind oyster reef dams in the marsh creeks.
Photo is of Barn Creek behind the University of Georgia Marine Institute on Sapelo Island at low tide. By E. Sherr
The source of these pops is the lethal weapon of a strange-looking shrimp ubiquitous in salt marsh estuaries: Alpheus heterochaelis, the snapping shrimp. This dangerous crustacean is also called the pistol shrimp, for good reason.
Reaching about two inches in length, Alpheus is distinguished from other shrimp by its lack of a long rostrum (a beak-like structure extending past the eyes) and by its one large claw. The genus name, heterochaelis, means 'differently clawed,' and boy is it ever.
The claw, almost half the length of the body, is an amazing weapon: the shrimp equivalent of a Saturday night special. The claw has a tooth that fits tightly into a socket. The tooth can be cocked just like the hammer of a gun; when it is suddenly popped into the socket, a powerful snapping sound is made. Alpheus lives in a subtidal burrow, lying in wait at the entrance. When its long antennae protruding from the burrow's entrance detect a small fish or other likely prey nearby, the shrimp sneaks out and lets its victim have it.
The sudden shock wave from the claw's snap stuns the prey, which the shrimp then finishes off and drags back down its hole for a leisurely meal. At low tide, smaller grass shrimp and young killifish massed in tidal creek pools behind oyster reefs are easy pickings for the pistol-packing shrimp, resulting in the fusillage of claw-snaps heard throughout the marsh.
Photo above of snapping shrimp, edited slightly, from Creative Commons: https://www.flickr.com/photos/crabby_taxonomist/ Alpheus heterochaelis Dorsal ViewCollecting at night from mixed Halodule/Thalassia bed at Frank Pate City Park, Port St. Joe 10 August 2011