Sometimes scientific discoveries happen entirely by accident. Researchers from the Okinawa Institute of Science and Technology Graduate University (OIST) were conducting a routine cleanup of a squid tank recently when they noticed something a little curious. As they wiped away the deep-green film of algal growth from the glass sides of the tank, they released that the squid were changing colour to match their surroundings. While swimming in the newly cleaned section of the tank the squid adopted an almost-transparent appearance, but the moment they ventured back to the algae-darkened area they quickly turned a deep shade of green.

The discovery marks the first time squid in a laboratory setting have been recorded using their camouflage skills to match the colour of a substrate, and it opens up "research avenues on how squid see and perceive the world around them," the team stated in a press release

Squid spend much of their time in the open ocean where their camouflage skills are not always on full display. Their pelagic lifestyle doesn't lend itself very well to a lab environment and, as a result, most studies on cephalopod camouflage have focused on species like octopuses and cuttlefish. However, a team from the Physics and Biology Unit at OIST have been raising a shoal of oval squid in captivity since 2017 and were able to use these colour-morphing masters to deduce the latest findings.

The squid, known locally as Shiro-ika, are one of three species of oval squid found in Okinawa. In the open ocean where they are usually found, they have a light-coloured appearance as they try to blend in with the clear water and flickering sunlight found near the surface. "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,” explained one of the three first authors, Dr. Ryuta Nakajima, OIST visiting researcher. "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."

After stumbling across the colour-changing abilities of the squid, the researchers set up a controlled experiment to confirm their findings. Squid were placed in a half-cleaned tank and two cameras were set up to monitor their behaviour. The footage clearly showed that as the cephalopods swam into the darker areas of the tank, their colour transformed to blend in to the background. 

"This effect really is striking. I am still surprised that nobody has noticed this ability before us," Dr. Zdenek Lajbner, one of the authors of the study stated in a press release. "It shows just how little we know about these wonderful animals."

The team are hopeful that their study will spark further research into the visual capabilities of the squid as well as gaining a better understanding of how these animals use different substrates to remain hidden from predators.

"We look forward to continuing to explore the camouflage capabilities of this species and cephalopods more generally," said Prof. Jonathan Miller, Principal Investigator of OIST’s Physics and Biology Unit and the senior author of the research article.

Header image: George Berninger Jr.