Flashing and flickering squid

“Humboldt squid can be very cannibalistic,” Stanford University graduate student and researcher Hannah Rosen told me via email, “and if they sense a weakness in another individual they will attack and eat it.”

I had asked her to speculate on the fate of one particular Humboldt squid. “Though I can’t say with any certainty what its fate was since the camera was ripped off, I’d say there is a good chance it was killed,” she replied.

Rosen and a team of researchers from Stanford University and National Geographic recently reported the results of a study in which they outfitted three Humboldt squid, large cephalopods that can grow up to four feet long (not including their arms and tentacles – scientists report squid sizes in terms of the length of the mantle, the torpedo-shaped part of the body above the head), with video cameras so they could spy on their underwater color-changing behavior without the interference of divers or submersible vehicles.

Two of the squid were lit only by natural light filtering down through the water; the recordings they gathered showed Humboldt squid exhibiting two types of dynamic color-changing behavior: ‘flashing,’ a whole-body, rhythmic and rapid change in color, and ‘flickering,’ a wave-like scattering of color across the skin that, the authors write, “mimic[s] reflections of down-welled light in the water column,” much like the play of light against the bottom of a pool. (Humboldt squid chromatophores, the small organs in their skin that they reveal to change their appearance, are a single, reddish-brown color; unlike some other species of squid which have chromatophores of many different colors, Humboldt squid are either white, when their chromatophores are hidden, or red, when they’re exposed.)

Flickering, the authors suggest, may be a form of camouflage for the squid, helping them to blend into their environment and perhaps avoid being eaten. Flashing occurred primarily when the squid were in groups, suggesting that it may be a form of communication; the video recordings captured a number of interactions between squid, including physical contact, possible mating attempts, and arm-splaying that appeared to be directed toward the squid wearing the camera.

One of the cameras also captured an aggressive episode of “numerous attacks” in which, the researchers write in their paper, “several other squid . . . tore the camera package off the camera-bearing squid shortly after it was released.”

That was the squid I asked Rosen about. The scientists had equipped that squid’s camera with a red LED light so they wouldn't have to rely on natural illumination, allowing them to observe nighttime behavior. The red light apparently had the unintended consequence of aggravating the surrounding squid, leading to the attacks. 

“We were hoping the red light would be out of their visual range,” Rosen said in an email, “but were obviously wrong.”

Rosen and her team didn’t give up there, though. Last year they tried infrared lighting, which did not lead to the same problems as the red LEDs; unfortunately, Rosen said, “it also didn’t provide enough light to really see anything that was happening around the squid.”

Moving forward, Rosen intends to continue studying Humboldt squid, their color-changing behavior, and how they control their chromatophores. In the meantime, she hopes that non-scientists embrace the importance of studying animals that experience the world in a completely different way than humans do.

“It’s easy to assume an animal is stupid just because of how it looks,” she said, “but just because an animal doesn’t act the same way we do, that doesn’t mean it isn’t smart, it might just have skills we can’t imagine because they aren’t something we would ever need.”

Researchers attached a video camera to a cloth sleeve slipped onto the mantle of each squid. The cameras were programmed to detach and float to the surface at a specified time. 

(Image by Joel Hollander)