Octopuses and cuttlefish are famous masters of disguise, known for their ability to change color based on their activity or surroundings, allowing them to blend so well into the environment that they become virtually invisible. Though scientists suspected that squids also have this ability, it was only recently that experiments confirmed that these animals share the same camouflaging abilities as their cephalopod peers.
Squids like to live in the open ocean, where their light skin perfectly blends with the water and flickering sunlight above. But this appearance would make them an easy target on the ocean floor, so biologists believed they may also use some adaptive camouflage. The problem is that no one has seen such a thing in action before because squids are challenging to observe on the ocean floor and they are notoriously difficult to keep in captivity. Camouflage is much easier to study in octopuses, the favorite pets of marine biologists, so squids have been largely ignored — until now.
Japanese researchers at the Okinawa Institute of Science and Technology Graduate University (OIST) bred oval squids native to Okinawa, which they kept in a tank. One day, while they were cleaning algal growth from the tank, the researchers were shocked to notice that the squids were changing color to match the appearance of the algae.
This accidental discovery spurred them to perform a controlled experiment. Several squids were kept in a tank which was cleaned in one half, the other half staying covered in algae. An underwater camera was placed inside the tank as well as a regular camera suspended above the tank to capture any changes in color.
When the squid swam in the cleaned section, they retained their characteristic light color. But when above the large, their skin promptly turned darker.
“This effect really is striking. I am still surprised that nobody has noticed this ability before us,” said another first author, Dr. Zdenek Lajbner. “It shows just how little we know about these wonderful animals.”
The squid involved in this research is one of three species of oval squids. Known as Shiro-ika to local Japanese, this squid plays a major economic and cultural role in the Okinawa community. It was the local fishermen who first identified the three distinct species of oval squids in Okinawa, long before trained biologists studied them.
The fact that ocean floor environments may play an important role in the survival of squids could contribute greatly to their conservation. “If substrate is important for squids to avoid predation then that indicates that increases or decreases in squid populations are even more tied to the health of coral reefs than we thought,” said Dr. Ryuta Nakajima, a visiting researcher at the Okinawa Institute of Science and Technology Graduate University.
The findings appeared in the journal Scientific Reports.