10 November 2016

Underwater's Ultimate Weapon

Listen to this audio recording below from Radiolab [1]. Start from 2:00 and end at 3:25.

What did you hear?

Rice pops? Twigs being burned? Frying bacon?

No – they are snapping shrimps, or rightfully called “pistol” shrimps which belong to the family Alpheidae. Do the sound even hint to a deadly weapon?

For starters, a snapping shrimp is a tiny creature, reaching one to two inches – just half of your finger [4]. Now it gets scarier: it has a distinctive large claw which it uses to stun a prey instantaneously! The cracking sound produced is what you hear during low tide in shallow waters. Some species live mutually with gobies in burrows: the shrimp provides a home for the goby, while the fish confers protection to shrimp against predators [2].

Why do these shrimps make an incessant sound? 

In 2000, European scientists discovered that the sound is produced from the formation of cavitation bubble released when the claw rapidly snaps shut [3]. Charged with a speed of up to 100 km an hour [1,3,4], the bubble can go for a swift kill in a matter of 300 microseconds [3]. As the pressure stabilizes, the bubble pops with a loud bang reaching about 220 decibels [1, 5]. That is equivalent to the sound of a jet engine [1], enough to break small jars [4]. And yes, it’s louder than a gun shot which is around 150 decibels [7]. It actually competes with the sperm whale as the loudest animal in the ocean [4].  

It emits not only a ‘deafening’ sound but an ultra-fast light when the bubble collapses. It is thought to exhibit sonoluminiscence - emission of short bursts of light [4] caused by a strong sound field [3]. If it were to be seen at the time of collapse, the temperature inside the bubbles must be a least 5,000 degrees Kelvin, comparable to the surface of the sun at 5,800 degrees Kelvin. The ephemeral flash of light lasts no longer than 300 picoseconds (a picosecond is one trillionth of a second) [3]. 

The violence of it all is lies on the sheer extremes of temperature and pressure before bursting – a truly impressive and deadly weapon. Now that’s intimidating.

Credit: National Geographic

Below is pistol shrimp in action, releasing its deadly, supersonic bubble [6].

Here’s another interesting feat.

Pistol shrimps helped the Americans win World War II. Yes, you read it right. Since the crackling sound they produce is intense enough to disrupt underwater communication, US Navy submarines used the shrimp beds to interfere with the sonar, therefore attacking the Japanese while hiding on their makeshift invisibility cloak [1,2]. They even installed speakers on their ships to mirror the shrimps’ sounds! [1]. 

Awesome, isn't it?

To know more about snapping shrimps or pistol shrimps, visit SeaLifeBase.

Written by:

[1] Iono.fm. (2016, November 10).  Bigger than bacon [Audio file]. Retrieved from https://iono.fm/e/286830
[2] Riley, A. (2016, January 29). This shrimp is carrying a real-life working stun gun. BBC Earth. Retrieved from http://www.bbc.com/earth/story/20160129-the-shrimp-that-has-turned-bubbles-into-a-lethal-weapon
[3] Roach, J. (2001, October 3). Snapping shrimp stun prey with flashy bang. National Geographic. Retrieved from http://news.nationalgeographic.com/news/2001/10/1003_SnappingShrimp.html
[4] Anirudh (2013, February 13). 7 interesting facts about pistol shrimp or snapping shrimp. Retrieved from https://learnodo-newtonic.com/pistol-shrimp-facts
[5] Ocean Conservation Research (2016). Snapping shrimp. Retrieved from http://ocr.org/sounds/snapping-shrimp/
[6] Nat Geo Wild. (2013, April 11). World’s deadliest – amazing pistol shrimp stun “gun” [Video file]. Retrieved from https://www.youtube.com/watch?v=KkY_mSwboMQ
[7] Simon, M. (2014, July 11). Absurd creature of the week: the feisty shrimp that kills with bullets made of bubbles. Wired. Retrieved from http://www.wired.com/2014/07/absurd-creature-of-the-week-pistol-shrimp/