Some octopuses intimidate their neighbors by turning black, standing tall and looming over them threateningly, like an eight-armed Dracula.
That's according to a study published Thursday that helps show that octopuses aren't loners, contrary to what scientists long thought; some of the invertebrates have an exciting social life.
"There can be over a dozen octopuses or more at this site," says David Scheel of Alaska Pacific University. "Generally, during the Australian summer there are more and we see a lot of activity then."
A local diver, Matthew Lawrence, first noticed there was a lot of octopus interaction going on there. His observations piqued the interest of Scheel, who is a marine biologist, and Peter Godfrey-Smith, a philosopher who had been thinking about octopus consciousness.
The research team eventually recorded 52 hours of underwater video, showing 186 octopus interactions.
"I took a look fairly early on at one sequence in which one octopus approaches another in a fairly menacing way," recalls Scheel. "He gets all dark, stands up very tall, and the other octopus crouches down and turns very pale. And then, when the approaching octopus persists, the other one flees. And this is immediately followed by the first octopus approaching a third octopus that's nearby. And the third octopus turns dark and doesn't crouch down. He just stays where he is, holds his ground."
It looked like they were signaling to each other, says Scheel. That was surprising, because the changing color patterns on an octopus's body are generally just associated with camouflage from predators. As the researchers watched more video, they became convinced.
"The dark color and some of the behaviors that go with it are associated with aggression, or at least approach," Scheel says. "The paler colors signify that the octopus is not going to stand its ground — that it's going to retreat or withdraw."
An aggressive octopus would stretch out the web of its tentacles very wide, to look as big as possible. "And, of course, it's got these scalloped edges between each arm," says Scheel, adding that the octopus would also stand very tall and turn black.
"It looked to me, for all the world, like Dracula approaching his prey," he says. "In my early notes I was calling this the Nosferatu display."
Sometimes an octopus will even do this while standing on the highest available ground, he adds — a piece of junk that's sticking up out of the seafloor.
Until about 15 years ago, scientists believed that octopuses were pretty much asocial.
"When they interacted, they either mated or ate each other," says Crissy Huffard, a senior research technician at the Monterey Bay Aquarium Research Institute in California. "That was the overriding idea."
But Huffard has done research on another octopus species that shows males display a black-and-white striped pattern when they're in the presence of another individual. "And that tends to send the signal, 'I'm male,' " she says. If the other octopus displays a similar body pattern, the male will be aggressive and fight. If not, then he'll try to mate.
She was interested in the threatening body posture that researchers observed in Australia.
"That's very cool to see," she says. "Octopuses are probably not as completely asocial as originally assumed. Their communication system reflects the fact that they're interacting on a fairly regular basis."
RENEE MONTAGNE, HOST:
Let's go to the sea now, into the secret life of the octopus. These creatures are famous for many things - their eight tentacles, their complex brains, the way they can change color and disappear in a cloud of ink. Plus, they have a reputation for being loners. NPR's Nell Greenfieldboyce has this report on a new study that shows just how wrong that is.
NELL GREENFIELDBOYCE, BYLINE: Off the southeast coast of Australia, there's a shallow spot with a lot of tasty scallops. It's a place where a species known as the gloomy octopus likes to hang out.
DAVID SCHEEL: There can be over a dozen octopuses or more at this site. Generally, during the Australian summer there's more.
GREENFIELDBOYCE: David Scheel is a marine biologist at Alaska Pacific University. He and two colleagues wanted to understand how these octopuses interact, so they've taken around 52 hours of underwater video. And right from the start, what they saw was dramatic.
SCHEEL: I took a look fairly early on at one sequence in which one octopus approaches another in a fairly menacing way. And he gets all dark, stands up very tall, and the other octopus crouches down and turns very pale.
GREENFIELDBOYCE: The pale one flees.
SCHEEL: And this is immediately followed by the first octopus approaching a third octopus that's nearby. And the third octopus turns dark and doesn't crouch down. He just stays where he is - holds his ground.
GREENFIELDBOYCE: As Scheel watched more video, he became convinced that octopuses use their bodies' color and posture to talk to each other. An aggressive octopus will turn black and try to look as big as possible, spreading out its tentacles. To him, it looks like an eight-armed Dracula looming over its prey.
SCHEEL: In my early notes, I was calling this the Nosferatu display.
GREENFIELDBOYCE: The researchers describe all of this in the journal Current Biology, and Crissy Huffard thinks it's pretty cool. She's at the Monterey Bay Aquarium Research Institute in California. And she says until fairly recently, scientists believed that octopuses were almost completely solitary, with pathetic social skills.
CHRISTINE HUFFARD: When they interacted, they either mated or ate each other. That was the overriding idea.
GREENFIELDBOYCE: But Huffard has done research on another octopus species showing that males take on a striped body pattern when they see another octopus. She thinks there's a whole lot left to learn about what happens when octopuses get together. Nell Greenfieldboyce, NPR News.
(SOUNDBITE OF SONG, "OCTOPUS'S GARDEN")
THE BEATLES: (Singing) I'd like to be under the sea in an octopus's garden in the shade. He'd let us in, knows where we've been, in his octopus's garden in the shade. I'd ask my friends to come and see. Transcript provided by NPR, Copyright NPR.