A new study shows that oysters can "hear" without actually having ears. This study, published in the journal PLos ONE, suggests that hearing is a bit common among molluscs and other marine animals and noise pollution in our oceans is worse than previously thought.
To see if the oysters really hear or not, Jean-Charles Massabuau at the University of Bordeaux in France and his colleagues placed 32 Pacific oysters in tanks and played different sounds with different frequencies and loudness between 10 and 20k hertz. When stressed or threatened, the oysters usually close their valves and the researchers put accelerometers on the oysters to track their movement.
When exposed to varying sounds, the oysters typically responded to frequencies between 10 and a thousand hertz. According to Massabuau, they don't hear like we humans do, but perceive sound through the stratocyst, which is an organ that picks up movement and vibration.
"Our results show that in shallow waters, they must be able to hear breaking waves and water currents," says Massabuau. The oysters would open up when tidal water comes, which brings in food for the molluscs. The oysters would also be able to hear thunderstorms, which would explain the way oysters usually spawn during lightning and thunder and they might also hear the sound of predators approaching. "Lobsters or fish, which feed on young oysters, produce wounds in the oyster hearing range, if they're close enough," says Massabuau.
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