The Humboldt squid uses pigment sacs on its skin to "flash" and to "flicker," both previously unknown behaviors, according to a study published today in the Journal of Experimental Biology. These displays were caught on cameras mounted on top of three 6-feet-long squid by a group researchers at Stanford University and at the National Geographic Society. According to the scientists, the squid might be using the flashing to communicate with others, whereas the flickering might be used as camouflage.
"Nobody had ever attached cameras onto free-swimming squid before."
"This is pretty much the first study of its kind," says Hannah Rosen, a squid researcher at Stanford University and a co-author of the study. "Nobody had ever attached cameras onto free-swimming squid before."
Researchers already knew that this behavior was possible, but "anytime this was observed it was kind of under high stress situations," Rosen says. It's hard to see the Humboldt squid in their natural environment, since the species tends to hang out deep in the water column during the day; they only come up at night. So until now, the scientists weren't sure why the color displays happened. But by filming the squid using natural light and cameras for the first time, scientists saw the behavior in context. Two squid were filmed during the day, and one was filmed at night. Rosen only got to see the videotapes, but she still thinks that "seeing them perform in the natural environment during the day is pretty unique."
Humboldt squid, flickering. (Stanford University / National Geographic Society)
The squid's skin color changes over the course of their displays, and the resulting patters also change in a predictable way. The flickering behavior resembles what happens when light reflects at the bottom of a pool, Rosen says. This is why the scientists think the behavior serves as camouflage — it might serve to trick its prey into thinking that the squid isn't anything worth fleeing from. The flashing, on the other hand, tends to happen more often when other squid are around (pictured above). This hints that it might serve as a communication tool.
We already know how squid produce these patterns: they contract their chromatophores — pigment-containing cells located on the skin that connect to nerves in the animals' central nervous system. The flashing and flickering is activated by these nerves in much of the same way that human brain sends signals to the hand to make it move, Rosen says. "All squid species have these chromatophores," she says.
"But maybe give your calamari more respect next time you're enjoying it."
This study wasn't just about analyzing video clips. The devices that were mounted on the squid also recorded the squid's acceleration, the water's temperature, and depth data. The researchers hope that these data will help them find out more about the Humboldt squid's behavior in general. This is important because Humboldt squid are a commercially and ecologically important species, Rosen says. "They are one of the most fished species in the world," she says. Learning more about them is therefore "beneficial to the fisherman trying to catch them."
Rosen says that squids are a lot more complicated than some people think. "It's easy to look at an invertebrate and say: ‘it doesn't have any bones,' ‘it looks bizarre,' or 'it's just a snail,'" she says. But cephalopods — squids, octopuses, and cuttlefish, for instance — are thought to be a lot more intelligent that the lowly snail. "So I wouldn't discourage people from eating," she says, "But maybe give your calamari more respect next time you're enjoying it."