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Auckland University researchers say they have discovered why underwater ambient noise around New Zealand's coast gets louder twice a day.
Craig Radford and Andrew Jeffs recorded the sounds made by reef animals, then compared them with the background sound in the natural reef, and found kina were the culprits.
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 as 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," Dr Jeffs said.
Ambient noise generated around the coast is thought to play a role in guiding baby fish and crustaceans that have hatched at sea to a suitable habitat in which they can settle.
Researchers have speculated that increased intensity of biological sounds on a reef at dusk, new moon and summer could be transmitted further offshore.
- NZPA
