In the midst of the mud-bottomed waters of Jervis Bay in southeastern Australia is a spot that researcher Peter Godfrey-Smith has named "Octopolis."
Octopolis consists of thousands of shells, the remains of bivalves that the site's resident octopuses have eaten. And it keeps getting bigger, making room for even more octopuses to move into the area and create small dens in which to live.
All of this forces the octopuses to interact. In a study published Thursday in the journal Current Biology, researchers have shown that the octopuses in this location, which are known as common Sydney octopuses (Octopus tetricus), signal and display to one another in dramatic ways as they spar and face off. It's the first published evidence that octopuses use colorful signals to communicate with one another during combative social interactions, says David Scheel of Alaska Pacific University, who authored the paper along with Godfrey-Smith and Matthew Lawrence, who first discovered Octopolis in 2009.
In the center of Octopolis lies a slightly raised area, perhaps the remains of a rusted anchor or other piece of human detritus. In the paper, the scientists show that octopuses often go to this area to "display," raising up their body, spreading their legs and turning themselves a dark brown color. This is done during a confrontation with another octopus, and usually the one that doesn't do the displaying retreats, Scheel says.
Sometimes the second octopus, who doesn't make the first display, also turns dark brown, and the first retreats. Or, the two come to blows. But this isn't too common; in the hundreds of interactions the team filmed for its study, the animals only sparred a couple dozen times. These fights consist of wrestling matches, usually quite brief, after which one animal slinks away, Scheel says.
Less than two decades ago, scientists still considered octopuses to be entirely asocial, so much so that research to the contrary garnered bad reviews, says Christine Huffard, a researcher at the Monterey Bay Aquarium Research Institute who wasn't involved in the paper. But this study, like other recent ones, shows that octopuses are much more social than previously thought.
