What sound means to squids
London: Marine biologists have started prying on squids’ world to find out how these creatures hear and how they respond to sounds in the ocean.
It is only in recent times that scientists have accepted that cephalopods have any auditory capability at all.
But new experiments have demonstrated that noises of varying loudness and frequency will elicit a range of behaviours in the animals - such as jetting or inking, and even a change of colour.
Dr Aran Mooney from the Woods Hole Oceanographic Institution (WHOI) of Massachusetts, US insisted that squids represent something of a keystone species in the ocean, sitting right at the heart of many food webs. If they are not the predator in those webs, they will almost definitely be the prey.
And that makes it vital to know if anything we may be doing in the oceans could be unsettling them.
“We produce a lot of noise through exploration of the oceans, scientific research, oil drilling, gas exploration and commercial shipping,” the BBC quoted Dr Mooney as saying.
“A lot of that is low-frequency noise, which is what squid detect. And if we’re influencing these animals then presumably we could change their behaviour.”
Previous work at WHOI’s Sensory Physiology and Sensory Ecology Lab had stated that squid could hear sounds in the range of 50Hz to 500Hz but they are best below 300Hz. It is the same kind of range as fish.
The squid make use of two narrowly spaced organs called statocysts to sense sound.
“I think of a statocyst as an inside-out tennis ball,” explained Dr Mooney.
“It’s got hairs on the inside and this little dense calcium stone that sits on those hair cells.
“What happens is that the sound wave actually moves the squid back and forth, and this dense object stays relatively still. It bends the hair cells and generates a nerve response to the brain.”
The latest research has tried to estimate exactly what sound means to the squid, and how they might use it.
In a tank in his lab, Dr Mooney played noises of varying loudness and frequency to the animals, and watches for their response.
He has been able to map how the different levels of sound will trigger the cephalopods into different behaviours.
“They react in about 10 milliseconds. That’s really fast; it’s essentially a reflex. That’s really important in terms of behavioural responses because they’re not thinking about processing it; they’re not deciding whether they should react - they’re just doing it.”
“The responses can be really dynamic. They can be a change in colour; they can be jetting (moving quickly) or inking responses. Squid are also very cool because you can look at a range of colour changes - is it a really startling colour change or a more subtle change?
“Squid can probably use their hearing to find their way around the environment - to sense the soundscape of the environment; for example, to find their way towards a reef or away from a reef, towards the surface or away from the surface,” he added.
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