A team led by Jean-Charles Massabuau from University of Bordeaux in France decided to investigate whether oysters have a sense of hearing.
On one level this might seem like a rather recondite pursuit, and one destined to end in frustration. There has, over the years, been plenty of research into the hearing abilities of other sea creatures, especially fish, but almost none into that of molluscs.
One of the reasons for this lies in the very nature of the problem.
“Whether hearing is present in non-arthropod invertebrates … is still controversial and difficult to decide,” wrote neuroscientist and evolutionary biologist Bernd Budelmann in 1992.
“Basically the problem lies with the definition of underwater sound and of underwater hearing.”
Despite these very real problems, however, Massabuau and his team decided to investigate whether oysters can hear.
The species has considerable economic and cultural value around the world, and a key role to play in marine ecosystems. The question of whether it is being impacted by increasing levels of human-made underwater noise pollution is one well worth asking.
To find out if the molluscs are sensitive to sound, therefore, the scientists set up two 16-member groups of them in tanks full of running salt water. The tanks were fitted with suspended speakers, which pushed out a range of different single frequency tones at various volumes for three minutes at a time.
The effect on the oysters was measured by whether – and to what extent – they closed their shells when the sounds were running.
The team found that the animals were particularly sensitive to low frequency sounds, especially between 10 and 200 hertz, but didn’t react to higher ones.
(Which means that an oyster would make a very poor companion at a heavy metal concert, where the kick drum pushes out between 20 and 100 hertz, but would be unmoved listening to Franz Liszt’s Liebestraume for solo harp.)
The researchers suggest that this could be because such deep notes might be generated by the interaction of waves and rocks, triggering opening and closing behaviours in the oysters as tides rise and fall.
Unfortunately, they also include the range of sounds commonly emitted by cargo ships, underwater pile driving and wind turbines – raising the possibility that such anthropogenic noises might cause farmed oysters to react inappropriately, leading to damage.
In conducting their research Massabuau and colleagues were in one sense echoing earlier work by Charles Darwin himself.
As detailed in his 1881 book The Formation of Vegetable Mould through the Action of Worms, with Observations of their Habits the great naturalist spent many years investigating whether earthworms could hear.
Among other experiments Darwin placed the worms on trays and variously shouted at them, played the piano to them, and had his son honk a bassoon at close proximity.
At length, he concluded that common earthworms, whatever their other virtues, were stone deaf.
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