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The snapping shrimp (Alpheus heterochaelis) produces a loud snapping sound by an extremely rapid closure of its snapper claw. One of the effects of the snapping is to stun or kill prey animals. During the rapid snapper claw closure, a high-velocity water jet is emitted from the claw with a speed exceeding cavitation conditions. Hydrophone measurements in conjunction with time-- controlled high-speed imaging of the claw closure demonstrate that the sound is emitted at the cavitation bubble collapse and not on claw closure. A model for the bubble dynamics based on a Rayleigh-Plesset-type equation quantitatively accounts for the time dependence of the bubble radius and for the emitted sound.
The oceans may be deep, but they are not at all quiet (1). Sounds in the oceans include those of waves; rain, hail, and snow; and the biological sounds of fish, dolphins, whales, and snapping shrimp. The latter, in particular, produce the dominant level of ambient noise in (sub)tropical shallow waters throughout the world (2). These shrimp usually occur in such large numbers that there is a permanent crackling background noise, similar to the sound of burning dry twigs (3). The snapping sound can be heard day and night (4), with source levels as high as 190 (5) to 210 dB (6) (peak to peak) referenced to 1 Pa at a distance of 1 m. This severely limits the use of underwater acoustics for active and passive sonar, both in scientific and naval applications. The frequency spectrum of a snap is broad, ranging from tens of hertz to >200 kHz (5). The noise of snapping shrimp is therefore also used as a source for creating pictorial images of objects in the ocean through ensonification (7).
A snapping shrimp of the species Alpheus heterochaelis (-5.5 cm in size) is shown in Fig. IA. The shrimp produces the snapping sound by an extremely rapid closure of its large snapper claw, which may reach 2.8 cm in length, about half of its body size. The claw (Fig. lB) has a protruding plunger on the dactyl and a matching socket in the propus. Before snapping, the claw is cocked open by co-contraction of an opener and a closer muscle, building up tension until a second closer muscle contracts (8)....