Speaking of crustaceans, I learned something very cool the other day. This isn’t exactly news – it was reported in Nature in 2001 – but it’s news to me so I’m going to assume it’s probably news to most of you too.
One of the loudest sounds in the sea – quite possibly the loudest – is made not by any of the biggest creatures, such as whales, which is what you’d expect. No, that honour goes to a small species of pistol shrimp – Alpheus heterochaelis – no bigger than your finger.
The shrimp has one oversized claw, which creates an incredibly loud noise when it snaps it shut – about 200 decibels in volume. To put this in perspective, a jet engine at full blast is about 120 decibels. The shrimp use the sound to imobilize (and presumably deafen) their prey. A whole colony of the shrimp snapping together is loud enough to interfere with sonar equipment.
Scientists used to think that the noise was simply created by the snapping of the claw – but in 2000 they discovered that in fact the noise is created in a far more outlandish and fantastic way.
When the shrimp snaps its claw shut, it expels a jet of water from a hole in the claw, which can shoot out at up to 100 km an hour. A low pressure bubble is generated in the wake of this jet of water. When the bubble collapses under the pressure of the water around it, it produces intense sound waves (I believe this is known as inertial cavitation – but my understanding of fluid mechanics is pretty poor so don’t quote me on this).
But here’s the really cool thing: in 2001 researchers discovered that the bubbles collapse with such force that they produce tiny flashes of light.
Bubbles emitting light is nothing new – the phenomenon is known as sonoluminescence and it was first discovered in the 1930s, when physicists discovered by accident that subjecting small bubbles to ultrasound can create bursts of light.
But actual living creatures creating light in this way was new – biologists had never seen anything like it before (which is understandable considering that the light produced by the shrimp is not actually visible to the naked eye, and the whole process only lasts about 300 microseconds). Moreover, the laws of physics would dictate that the temperature inside the bubble is at least 5,000 degrees Celsius – as hot as the surface of the sun.
The researchers dubbed the phenomenon “shrimpoluminescence” – a cute play on the word sonoluminescence, and you can get more detailed descriptions of their experiments, plus photos and videos on their website.
The researchers told National Geographic that they don’t think the light bursts are of any biological significance, and are probably just an unintended side effect. That is most likely the case, and I don’t have any reason to believe that the light serves any real purpose (or that the shrimp themselves can even see it).
But still, I’m going to keep an open mind: nature is constantly surprising us, and I wouldn’t put anything past the inventive genius of evolution.