Standing tall, arms spread, changing colors—them's fighting words for an octopus .

Until recently, scientists thought the ocean dwellers didn't communicate with one another much at all. Rather than sending signals with their skin color and texture, octopuses—mostly solitary, except during mating—were thought to camouflage themselves with it.

But new video evidence suggests at least one kind of octopus—the common Sydney octopus (Octopus tetricus)—sends cues to its rivals about whether it will flee or flight. (Also see " Social Octopus Species Shatters Beliefs About Ocean Dwellers .")

David Scheel , a marine biologist at Alaska Pacific University, and colleagues shot the footage off southeastern Australia —the first evidence that fighting octopuses broadcast their intentions to one another.

Living to Fight Another Day

The common Sydney octopus, also known as the gloomy octopus, were thought to be very independent: When they do come together to mate, the female often eats the male afterward.

So the researchers were surprised that Sydney octopuses at their research site seemed to be interacting regularly.

"The expectation has been that if two octopuses meet, the big one eats the smaller one," says Scheel, who presented the initial findings at a recent Animal Behavior Society meeting in Anchorage, Alaska.

"But if octopuses encounter each other routinely, they can't cannibalize each other all the time."

Instead, it makes sense that the octopuses would need to communicate to either escalate or avoid conflict—which is exactly what the team found. (See "Journey of Octopus Discovery Reveals Them to Be Playful, Curious, Smart.")

Scheel and his colleagues observed a range of aggressive interactions between octopuses—everything from simply reaching out toward another octopus, to chases, to grappling. Of all these incidents, only a fraction were full-blown fights.

To get their point across, octopuses used a suite of dramatic behaviors such as spreading their arms wide, standing tall, raising their mantles—a structure that holds all their organs—like a crest above their eyes, and climbing on top of objects, the team observed. (See beautiful octopus pictures .)

The animals also changed color depending on their behavior: Aggressive octopuses tended to become darker, while fleeing octopuses were much paler.

"If one octopus signals that he's coming over and not going to back down, and the other signals he is going to run away, that can end the interaction," says Scheel.

"Whereas if they both signal that they're not going to back down, those are the [incidents] that tend to escalate."

Fight or Flight

This octopus body language likely occurs in more species, says Christine Huffard , a senior research technician at the Monterey Bay Aquarium Research Institute who was not involved in the new research.

"I would love to see people study this in different octopus species in the wild, but also research the mechanisms behind it," Huffard says. "It's hard to know whether it's an intentional versus a physiological response. For instance, we blush. We don't say, 'Hey, body, tell this person I'm embarrassed.' It's just something that happens." (" Watch: Stealthy Octopus Leaps From Water and Attacks Crab .")

Huffard agrees with Scheel and his colleagues that it's likely the octopuses are signaling to avoid costly battles.

When octopuses fight, the larger one nearly always wins.

"If you know from the beginning that you're probably going to lose or you're not really willing to give up an arm, you might as well tell your opponent that you don't want a fight."