Snapping shrimp may unlock key to reef survival

The snapping shrimp is just 4cm long, but it can produce a noise as loud as the sperm whale's song.

These crustaceans can be found in coastal waters around the world, and are particularly abundant in coral reefs, said University of Essex marine biologist Julius Piercy, who led a recent study on noise produced by reefs and how it is associated with the ecosystem's health.

Healthy reefs have a higher density of marine creatures producing noise, which makes them "louder", he explained.

"Because snapping shrimp species are so abundant, the snapping sounds they produce have been found to be associated with reef health in a number of recent studies," he added. In essence, more snaps equate to a healthier reef.

The shrimp are a good source of sound for the underwater camera dubbed Romanis, built by researchers at the National University of Singapore's Tropical Marine Science Institute (TMSI).

The camera uses sensors to detect changes in water pressure caused by sound waves.

When its 508 ceramic sensors detect such vibrations, they produce an electric signal, which is sent in real time to a computer on land via fibre-optic cables.

By timing how the sound wave is detected by the camera's various sensors, and how hard the water particles strike them, scientists can deduce where the sound comes from.

The Singapore researchers have found a way to use the sound collected to produce images, which can then be used to check for changes in the reef.

The snapping shrimp snaps its large snapper claws to hunt and communicate, and as a show of aggression.

But the sound it makes is not actually produced by the snapping of its claws.

When the shrimp contracts muscles to activate the claw, it forces a jet of water from the socket at high speed, which forms tiny bubbles.

As each bubble collapses, the temperature inside momentarily reaches the surface temperature of the sun, and produces - for an instant - a loud blast, said Dr Mandar Chitre, who heads the institute's Acoustics Research Lab.

Dr Piercy added: "Romanis can detect these sounds and also identify their location, which could be useful for identifying which parts of a reef are the most productive."

This article was first published on Feb 15, 2015.
Get a copy of The Straits Times or go to straitstimes.com for more stories.