Grazing sea urchins create ambient underwater noise on rocky reefs

Auckland University researchers say they have discovered why underwater recordings of ambient noise around the nation's coast gets louder twice a day.

Craig Radford and Andrew Jeffs recorded the sounds made by individual reef animals then compared them with the background sound in the natural reef, and found kina was the culprit. The scientists found grazing sea urchins produced the noise as they scraped algae off rocks, New Scientist magazine reported on its website. The bodies of kina act like resonance chambers, amplifying the sound of their chewing, they said.

"When they first come out I guess they're hungry, so they're eating with lots of gusto and making lots of munching noises," Mr Jeffs said.

Ambient noise generated around the coast, especially reefs, is thought to play a role in guiding baby fish and crustaceans which have hatched at sea to suitable habitat in which they can settle.

Researchers have speculated that increased intensity of biologically produced sound during dusk, new moon and summer could enhance the biological signature of a reef and transmit it further offshore. ..[3News.co.nz]