Saturday, January 3, 2009

I Have An Alpheidae And I’m Not Afraid To Use It!


Alpheidae is a family of caridean snapping shrimp characterized by having asymmetrical claws, the larger of which is typically capable of producing a loud snapping sound. Other common names of these species include pistol shrimp or alpheid shrimp.

The family is diverse, and is worldwide in distribution, consisting of about 600 species within 38 or more genera. The two most prominent genera are Alpheus and Synalpheus, with species numbering well over 250 and 100, respectively. Most snapping shrimp dig burrows and are common inhabitants of coral reefs, submerged grass flats, and oyster reefs. While most genera and species are found in tropical and temperate coastal and marine waters, Betaeus inhabits cold seas and Potamalpheops is found only in freshwater caves.

The snapping shrimp competes with much larger animals, like the sperm whale and beluga whale, for the title of 'loudest animal in the sea'. The shrimp snaps a specialized claw shut to create a cavitation wave that generates acoustic pressures of up to 80 kPa at a distance of 4 cm from the claw. The pressure wave is strong enough to kill small fish. It corresponds to a zero to peak pressure level of 218 decibels relative to one micropascal (dB re 1 μPa), equivalent to a zero to peak source level of 190 dB re 1 μPa at the standard reference distance of 1 m. Au and Banks measured peak to peak source levels between 185 and 190 dB re 1 μPa at 1 m, depending on the size of the claw. Similar values are reported by Ferguson and Cleary. The duration of the click is less than 1 millisecond.

The snap can also produce sonoluminescence from a collapsing cavitation bubble. As it collapses, the cavitation bubble reaches temperatures of over 5000 K.The light is of lower intensity than the light produced by typical sonoluminescence and is not visible to the naked eye. It is most likely a by-product of the shock wave with no biological significance. However, it was the first known instance of an animal producing light by this effect. It has subsequently been discovered that another group of crustaceans, the mantis shrimp, contains species whose club-like forelimbs can strike so quickly and with such force as to induce sonoluminescent cavitation bubbles upon impact.

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