Tuesday October 17 2017

Posted by BajaInsider.com on May 09, 2007
  • Alpheus heterochaelis
    Alpheus heterochaelis
  • Osiliscope output of a hydrophone capture of the snaping sound of the pistol shrimp
    Osiliscope output of a hydrophone capture of the snaping sound of the pistol shrimp

It's that noise that keeps some folks up at night when sleeping in a boat in the temperate waters of the Sea of Cortez. Some fear them for Fiberglass Termites but marine biologist Bill Martin fills us in on Snapping Shrimp or more scientifically amed Alpheus heterochaelis. Bill is a retired architect with a passion that drove him to a MS in 1999 and he and his wife Jean can can often be found poking around the tidal pools of La Paz.

The snapping shrimp (Alpheus heterochaelis) produces a loud snapping sound by an extremely rapid closure of its snapper claw. It was commonly believed that the sound is generated when the two claw surfaces hit each other. Research, however; shows that the sound, in fact, originates from the collapse of a cavitation bubble. During the rapid snapper claw closure a high-velocity water jet is emitted from the claw with a speed exceeding cavitation conditions. (Cavitation is a physical process that has long plagued ships' propellers.)

These critters are really loud (the popping of the cavitation bubbles) and when colonies of the shrimp snap their claws; the cacophony is so intense that submarines can take advantage of it to hide from sonar.

The shrimp use the sound to communicate with one another and to defend their territory. Additionally, they take advantage of the damage cavitation can do to stun their prey.

So no worries, they will not nibble through your boat’s hull!
We mentioned, didn’t we, that these critters are typically less than 1 inch in length?

IN THE ABOVE GRAPHIC: Hydrophone signal and b, light emission from the snap of a shrimp. The principal light-emission event coincides with the bubble collapse at t = 0. A second light flash coincides with the subsequent collapse of a cloud of bubbles, which is formed upon collapse of the principal bubble. c, Expanded view of the photomultiplier signal, showing the short pulse duration of 'shrimpoluminescence'. Within a range of 100 nanoseconds around the main peak, dimmer flashes of light are also evident; these may be due to emission of light from small bubble fragments formed during the violent collapse of the asymmetric cavitation bubble. Data analyses, R. M. Nelissen.

by:Bill Martin

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