Even Without Ears, Oysters Can Hear Our Noise Pollution

Study shows that certain frequencies of noise cause oysters to clam up

Wikimedia Commons

Of course, oysters don’t have ears. They've never heard the cowbell in Blue Oyster Cult’s “Don’t Fear the Reaper” or heard a recitation of the oyster classic, The Walrus and the Carpenter. But as Teresa L. Carey at PBS Newshour reports, a new study suggests that oysters may still suffer one of the downsides of having ears: noise pollution.

As Carey reports, researchers have long known that noise pollution can impact a range of sea creatures—and might even be responsible for some mass strandings of whales. Researcher Jean-Charles Massabuau of the University of Bordeaux and his team wanted to see if the sound created by boats, ships and other human activities on the water also impacted invertebrates.

Massabuau brought 32 Pacific oysters into his laboratory and used a loudspeaker to play various frequencies to the bivalves. Happy oysters tend to keep their shells cracked open; when they are stressed or face a threat, they slam their shells shut. So the team played a range of frequencies, measuring the how quickly the oysters closed their shells. 

It turned out, the oysters reacted most strongly to noises between 10 and 1000 hertz, showing the most sensitivity to sounds between 10 and 200 hertz. As Douglas Quenqua at The New York Times reports, those lower frequencies are often produced by cargo ships, seismic research, wind turbines and pile driving. Higher frequencies created by jet skis and small boats, however, did not seem to bother the animals. They published their results in the journal PLOS ONE.

“They are aware of the cargo ships,” Massabuau tells Carey. “What is for sure is that they can hear. The animals can hear these frequencies.”

Of course oysters don’t hear like humans. Instead, they have hair cells on the outside of their shells that sense vibration. The researchers believe the oysters use these hairs to detect things like breaking waves and ocean currents caused by rising tides giving them cues for when to feed.

“To hear the current arriving could prepare them for eating and digesting, possibly as when we hear and smell that somebody is preparing dinner,” Massabuau tells Quenqua. Noise pollution, however, could muddle the oysters' ability to read the tides, affecting their long term health. 

University of Hull marine biologist Mike Elliott, however, says it’s not clear if the noise pollution is having an impact. He has conducted similar studies on mussels and hermit crabs, who have similar reactions to certain frequencies. “It is quite a big leap from detecting a response [to sound] to if the animal is being harmed by it,” Elliott tells Carey. “The big challenge is converting this into a response that denotes harm to the organism.”

Massabuau agrees with this conclusion and plans to continue the study, focusing on whether the long-term exposure negatively impacts the oysters.

It's not just shellfish feeling the vibes. A 2015 study on general noise pollution in the oceans suggests it could be having significant impacts on a variety of species. In particular there’s growing evidence that air guns, which are used for seismic surveys, can cause hearing damage in whales and fish and stress from chronic noise pollution can negatively impact reproduction in many other species.

Perhaps, to help the creatures of the sea we first need to learn a lesson from the oysters, and just pipe down.

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