As a cruiser, we encounter many distinctive and at times bizarre conditions. Many times they are not what we believe they are. We had these dock mates a couple years back that were complaining to me about the galvanic decomposition on their vessel's underwater zincs while visiting a local marina. "It was so bad, you could actually hear the decomposition taking place; we'll never go to that marina for a second time." I just smiled and nodded my head.

As a boater, when you arrive in the balmier waters in Florida and further south, you may hear noisy crackling sounds coming from beneath your vessel's hull at night time. The sound can be surprising if you do not understand what you are listening to; is the vessel breaking apart you think? The sound might be described as cooking bacon in a frying pan or the crackling of dry wood burning.

On the docks, it is often said that these noises were merely krill eating the marine growth of your vessel's hull. Not so say marine biologists, it's the sound of snapping shrimp.

The shrimp, Alpheus heterochaelis, is a very small one inch crustacean that exists in the shallow waters of sub tropical seas. It has two claws', one larger than the other, which it uses to stun its prey, such as tiny crabs, by snapping the largest claw close. Researchers have, only a short period ago, found out how these tiny shrimp emit so much noise. At first they believed it was the clicking of the shrimps' enlarged claws. And it is ... basically. Now it is reported that the startling snap comes not from the clap of the claw itself but from a bubble created by the claws' quick closing movement. When the claw clamps closed, a spray of water emerges from a gap in the claw, creating a bubble. As the force stabilizes, the bubble bursts with a piercing boom; it's the cavitation from the water created by the fast closing. Similar to the cavitation from your vessel's prop, the water from the snapping claw creates tiny cavitation bubbles. As soon as the bubbles explode, the telltale snap is created. The whole process, which was studied with the help of fast photography and sound equipment, purportedly occurs within 300 microseconds.

Additionally, a flash of light also takes place when the bubble collapses.

The flashing occurrence is thought to be similar to sonoluminescence, which is defined as the emission of brief bursts of illumination from bursting bubbles in a liquid when excited by sound. The researchers have called the shrimp's snapping as shrimpoluminescence. The scientists were not capable of seeing the flashes with the naked eye but they can't totally discount it. The possibility is there that people very close to the shrimp when the bubble collapses and whose sight is well accustomed to the undersea darkness might be able to witness it. The light flashes appear to have no real meaning, the researchers say, but are a side-effect of the bubble burst. The light discharge is nevertheless indicative of the extreme environment inside the bubble at bursting and because of this shows the importance of the event.

In balmy sub tropical waters, these minute shrimp are plentiful and loud - so noisy they may keep you wide awake at night. Snapping shrimp supposedly snap at 200 decibels, well above the human hearing pain upper threshold.

Hence the next time you're on board at anchor, listening to the roar under your boat, think of the thousands of snapping shrimp in the water beneath you, efficiently conducting their own symphony while stunning their quarry, protecting their territory, and communicating with other critters in the waters.