Wednesday, February 04, 2009

Pistol shrimps send out cracks of sound

One of the loudest ocean noises is created by the snapping or pistol shrimp, which inhabits tropical coastal waters. This ferocious underwater hunter, only about 2 in (50 mm) long, stalks small fish and knocks them out with stunning 'shots' of high-intensity sound. The immobilised fish tip over and the shrimp catches and eats them.

So loud is this sound that it has been known to set off sound detectors on navy submarines. In the South Pacific, fishermen are said to use the loud cracks of pistol shrimps on a reef to guide them home. The sound is made by one of the pistol shrimp's front claws, which is almost half as big again as the creature's body, although it is carried on a leg of normal size.

To produce the noise, a shrimp strikes together two parts of this enlarged claw, used both to stun prey and to defend its burrow.


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