A team of scientists in Japan captured video of squid camouflaging with their surroundings, much like octopuses and cuttlefish do. While squid in the wild are known to change colour, the scientists set up an experiment to confirm this camouflage ability in a laboratory.
Like other cephalopods, squids have thousands of chromatophores — colour-changing cells — under their skin. The chromatophores can swell and shrink to appear darker or brighter, allowing the animals to communicate with each other and blend in with their surroundings.
The species of oval squid the team studied, Sepioteuthis lessoniana, had never been observed doing this type of environmental camouflage. A team from the Okinawa Institute of Science and Technology Graduate University held the oval squid in captivity and witnessed the animals changing colour to match their tank. The research was published last week in Scientific Reports.
“Squid usually hover in the open ocean but we wanted to find out what happens when they move a bit closer to a coral reef or if they’re chased by a predator to the ocean floor,” said Ryuta Nakajima, a biologist at University of Minnesota Duluth and the lead author of the paper, in an Okinawa Institute release. “If substrate is important for squid to avoid predation then that indicates that increases or decreases in squid populations are even more tied to the health of coral reef than we thought.”
There are a couple of reasons scientists didn’t previously know the extent to which squid colour change with their environment. Squid can be difficult to raise in captivity, and, unlike octopuses and cuttlefish, squid tend to live in the open ocean, meaning there’s not much substrate to blend with.
The oval squid species the team was studying had never shown evidence of colour changing with its environment. According to Michael Vecchione, an invertebrate zoologist at the Smithsonian Institution and NOAA, the “related species in the Atlantic, Sepioteuthis sepioidea [the Caribbean reef squid], has been observed a lot, and there’s been a lot of descriptions about its behaviour and colour patterns and so on, but it’s almost entirely based on field observations.”
“As far as I know, it’s the first of this kind [of camouflage] that’s been done in controlled laboratory conditions,” Vecchione said in a phone call.
In their natural habitat off the coast of Okinawa, the oval squid are light in colour, reflecting the sunlight filtering through the ocean surface. But kept in a tank, the squid were able to imitate local surfaces.
When the researchers were cleaning the squid tank, they realised the animals’ colours were changing depending on whether they were hovering over the algae-covered side of the tank or the clean side.
The researchers then created an experiment so they could document that colour change, intentionally making one side of the tank algae-covered and the other side spotless. On the algae side, the cephalopods turned a deep green, but when they swam to the clean side, they became almost translucent.
“This effect really is striking. I am still surprised that nobody has noticed this ability before us,” said Zdeněk Lajbner, a biologist at the Okinawa Institute and a co-author of the paper, in an institute release. “It shows just how little we know about these wonderful animals.”
Often overshadowed by their intelligent and patient cousins, some squid are finally divulging their secrets, at least in captivity. How these behaviours may be different in the wild is another question to explore.
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Editor’s Note: Release dates within this article are based in the U.S., but will be updated with local Australian dates as soon as we know more.