The tiger pistol shrimp, Alpheus bellulus, is a species of marine shrimp most notable for the way it captures its prey. It uses acoustic cavitations* to focus a wave of sound to stun prey animals. Usually less than an inch in length, these diminutive shrimps have two types of claws- a typical pincher and the other an enlarged claw called the ‘snapper’, which can generate an underwater shockwave capable of stunning smaller shrimps. Once its prey is stunned, the pistol shrimp can then easily capture it.

Source: http://www.smh.com.au/ftimages/2008/10/09/1223145521935.html

In an episode of BBC weird nature, “Pistol shrimps sonic weapon” , was a segment that unveiled the science behind the workings of the pistol shrimp’s snapper claw, which has been described as a lethal sonic weapon.  As seen in the video, the pistol shrimp is capable of dealing a knockout blow from a distance. When the pistol shrimp snaps its claw shut, a high-velocity jet of water is fired and low-pressure bubbles are created in its wake. As these bubbles collapse, they momentarily reach the temperature of the sun and a sound louder than a jet engine is produced. The shockwave created by this implosion then stuns the pistol shrimp’s prey.

BBC Weird Nature video – Pistol shrimp and the sonic weapon

What I found intriguing about this video was how a seemingly insignificant marine creature is capable of producing a sound so deafening that it can not only capture its prey without contact but also interfere with the use of underwater acoustics by larger marine creatures such as dolphins. Interestingly, the use of sonic frequencies to stun other animals is also seen in other marine creatures. A study by Janik (2005), found that bottlenose dolphins also “emit particular sound waves to stun its prey”.  Though the pistol shrimp is not the only marine creature that uses sonic frequencies to debilitate its prey, it remains unique in the sense that the sound produced by a single snap of its claw is among the loudest emitted by marine creatures. In fact, the pistol shrimp’s snapper claw is reportedly capable of producing a sound louder than the sperm whale, which is known to be one of the loudest animals in the sea. This makes the pistol shrimp truly one of the loudest marine animals alive.

* Acoustic cavitations – refers to the formation of vapour filled bubbles in a liquid that can generates acoustic pressures. When the pistol shrimp “snaps its specialized claw shut,  it creates a cavitation bubble that generates acoustic pressures of up to 80 kPa at a distance 4cm from the claw which is strong enough to kill small fishes”. Source: http://en.wikipedia.org/wiki/Pistol_shrimp

References:

Acoust, J., & Witlow, W. (1998). The acoustics of the snapping shrimp Synalpheus parneomeris in Kaneohe Bay. ASA digital library, vol 103, Issue 1, pp. 41-47.

Derbyshire, D. (2008). Deadly pistol shrimp that stuns prey with sound as loud Concorde found in UK waters. Retrieved March 30, 2010 from http://www.dailymail.co.uk/sciencetech/article-1085398/Deadly-pistol-shrimp-stuns-prey-sound-loud-Concorde-UK-waters.html

Definition of acoustic cavitation:  http://www.answers.com/topic/acoustic-cavitation

Image of Pistol shrimp: http://www.smh.com.au/ftimages/2008/10/09/1223145521935.html

Janik, V. (2005). Underwater acoustic communication networks in marine animals. UK: Cambridge University Press.

Pistol shrimp sonic weapon, BBC Wildlife weird nature http://www.youtube.com/watch?v=XC6I8iPiHT8

Norris,K &Mohl, B. (1983). Can Odontocetes debilitate prey with sound?. The American Naturalist. Vol. 122, No. 1 pp. 85. Retrieved March 31,2010 from http://www.jstor.org/pss/2461008

Unknown. (2010). Tiger pistol shrimp. Retrieved March 31, 2010 from http://www.aboutfishonline.com/articles/tiger-pistol-shrimp.html