This news release is also available in French.
The oceans' shallow waters are noisy places, what with the waves, rain, and those chatty marine mammals. Loudest of all are the colonies of snapping shrimp, whose underwater cacophony is the bane of military and scientific efforts to "see" through the ocean using sonar. In the 22 September issue of the international journal Science, a team of researchers reveals the surprising trick behind these creatures' noisemaking.
Snapping shrimp have one normal claw and one large snapper claw that can be up to half its body size, making the shrimp look like it's wearing an overgrown boxing glove. The claw stays cocked open until a closer muscle contracts, causing the claw to close with lightening speed.
The shrimp uses its snap to stun its prey, defend its territory, and communicate with other shrimp. Colonies of these shrimp usually are so dense that they produce a constant crackling background noise, similar to the sound of burning dry twigs.
Until recently, scientists had assumed that the snapping noise occurred when the two parts of the claw banged shut. Now, however, a team of physicists and a biologist have discovered that the noise, in fact, comes from the collapsing of small bubbles generated by the claw's closing motion.
The bubbles form through a process called cavitation, which occurs when objects move quickly through fluids. It's primarily known for damaging ship propellers and pumps, because the energy released from the tiny implosions pits and weakens metal surfaces.
The idea that shrimp snaps might come from cavitation germinated at a colloquium in Munich, where Detlef Lohse, of the University of Twente, in the Netherlands, had just given a talk on sonoluminescence, the process by which bubbles in a liquid emit light when excited by sound. Biologist Barbara Schmitz, of Technisch
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Contact: Ginger Pinholster
gpinhols@aaas.org
202-326-6421
American Association for the Advancement of Science
21-Sep-2000