While octopus and cuttlefish are famous for their use of camouflage as a defense mechanism, another cephalopod – the squid – has never been reported to display such abilities. However, a new study led by the Okinawa Institute of Science and Technology Graduate University (OIST) has now found that squids can camouflage by matching the color of a substrate in order to hide from predators.
“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 study lead author Dr. Ryuta Nakajima, a visiting researcher at OIST. “If substrate is important for squid to avoid predation than that indicates that increases or decreases in squid populations are even more tied to the health of coral reef than we thought.”
Since squid tend to live in the open ocean and are notoriously hard to keep in captivity, laboratory studies of the behaviors of these animals have been scarce. However, since 2017, researchers at OIST have been culturing a species of oval squid in captivity. This species – known as Shiro-ika – is one of the three species of squid found in the Okinawa region.
Dr. Nakajima and his team noticed almost accidentally this species’ camouflage ability. While cleaning the tank where the squids were kept to remove algal growth, the researchers were amazed to see that the animals were changing color depending on whether they were over the cleaned surface or the algae.
Afterwards, they performed a controlled experiment by keeping several squid in a tank half covered in algae. The results confirmed the initial observations: when the squids were in the clean side of the tank, they were light in color, but when they got close to the algae, they promptly became darker.
“This effect really is striking. I am still surprised that nobody has noticed this ability before us,” said study co-author Dr. Zdenek Lajbner, a biologist at OIST. “It shows just how little we know about these wonderful animals.”
This experiment suggests that, when in open ocean, squid are light in color, blending into the ocean surface and the flickering sunlight above, but when they move closer to the ocean floor, they most probably change in color, in order to match the darker environment. Further research is needed to explore in greater depth the camouflage abilities of this species, as well as of other cephalopods.
The study is published in the journal Nature Scientific Reports.