Friday, 18 August 2017

Langkawi Mangrove Tour: What's Popping In There?

There were many times when I was in the mangrove especially at low tide, I always wonder what made the popping sound like opening a bottle of champagne. Someone told me that it was the result of the air bubble popped when a crab emerged out of the burrow. Or could it be another creature like this one here that emerged in front of us be the answer?

We were checking out a nest of sedentary tube worm (polychaete) when it suddenly emerged out of the mud! It was a real lucky day for us especially for me. I am not sure if my guests were excited about it but I was surely 999% excited to see it. It didn't stay out very long for us until it dug itself into the mud again. 
Snapping Shrimp was starting to dig into the mud
Digging in!
Do have a closer look and try to notice one of its claw that is very much larger than the other. This is possibly the mangrove snapping shrimp (Family Alpheidae). However, I am not sure exactly of which species this one is.

This mangrove snapping shrimp we saw was less than 10cm. How a little crustacean can make a sound so loud and powerful to stun a fish and be heard many hundreds of metres away? 

According to the book PRIVATE LIVES - An Expose of Singapore's Mangroves:
It is because of its large claw that is packed with muscles and has a uniquely structured tooth on the finger that fits into a socket on the opposite. The muscles pull the toothed finger back and hold so much elastic force that when it is released, it hammers into the socket at an incredible speed and force, causing a high speed jet of water to emerge. The high speed causes a sudden drop of pressure (Bernoulli's principle) resulting in the formation of a tiny vapour bubble - what physicists call a cavitation bubble. The bubble violently collapses under the pressure of the surrounding water in a small "underwater explosion" causing a loud sound. During the collapse, the temperature in the bubble reaches the surface temperature of the sun! Snapping shrimps make these "snaps" to fend off rivals, deter enemies and rivals, and probably also to communicate with one another.

Researchers in the Acoustics Research Laboratory of the Tropical Marine Science Institute of the National University of Singapore have shown that in tropical waters, the snap density can range from 0.01 to 0.1 snap/second/square metre. Although this noise limits the performance of most traditional man made underwater acoustic systems, a novel technique known as "ambient noise imaging" uses this noise for underwater sensing.

Read about how the sound of the snapping shrimps interfere with the sonar detection in shallow seas and how a snapping shrimp rely on goby in Ria's WildfactSheets.

A HUGE THANK YOU to Iris Flock for taking the pictures of this snapping shrimp and kept your promise in sending them over to me. And also thank you to Ria for the confirmation. 

This is my first time seeing a real live snapping shrimp. Amazing! Hmm... I wonder if it tastes good...??

References: 
1) Private Lives - An Expose of Singapore's Mangroves
    Written by Peter K. L. Ng, Wang Luan Keng, Kelvin K. P. Lim
    Published by National University of Singapore

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