Until recently, scientists believed that members of the gloomy octopus species (Octopus tetricus) liked to fly solo. They thought the creatures, whose range extends from the waters off Sydney to New Zealand, met only once a year to mate.
But marine biologists discovered up to 15 gloomy octopuses together in a small type of city with dens made out of piles of sand and shells. They were spotted communicating, chasing each other, signaling and even evicting each other from dens. Researchers dubbed the village "Octlantis."
“These behaviors are the product of natural selection, and may be remarkably similar to vertebrate complex social behavior," lead researcher David Scheel of Alaska Pacific University told Quartz. "This suggests that when the right conditions occur, evolution may produce very similar outcomes in diverse groups of organisms.”
Octlantis, observed in Jervis Bay off the eastern coast of Australia, is about 10 to 15 meters under the water's surface; it's about 18 meters long and just over 4 meters wide. There are a few spots of exposed rocks and beds made of shells that were discarded from prey animals. Researchers found 13 occupied and 10 unoccupied dens at the site.
Another octopus city
A similar octopus town was discovered in 2009 just a few hundred yards away from the new octopus city. Up to 16 animals called this settlement — nicknamed "Octopolis" — home. In addition to several dens, it also contained a human-made flat object just under a foot long. Researchers thought at the time that maybe the octopuses needed an artificial object around which to build their settlement. Researchers weren't sure what it was, but thought it was possibly made of metal.
There's no interesting human object at the new location, however, to explain why the octopuses chose this spot to congregate. Researchers believe that it's the rock outcroppings found at Octopolis and Octlantis that made the locations attractive.
“At both sites there were features that we think may have made the congregation possible — namely several seafloor rock outcroppings dotting an otherwise flat and featureless area,” study co-author Stephanie Chancellor, a Ph.D. student in biological sciences at the University of Illinois at Chicago, said in a statement.
“In addition to the rock outcroppings, octopuses who had been inhabiting the area had built up piles of shells left over from creatures they ate, most notably clams and scallops. These shell piles, or middens, were further sculpted to create dens, making these octopuses true environmental engineers.”
Watching what goes on
In order to watch what happened in the octopus town, researchers dove down and placed four GoPro cameras at the new site to film for a day. They recorded 10 hours of footage that showed various types of social interactions among the tentacled inhabitants. Their findings were published in the journal Marine and Freshwater Behaviour and Physiology.
“Animals were often pretty close to each other, often within arm’s reach,” Chancellor said. “Some of the octopuses were seen evicting other animals from their dens. There were some apparent threat displays where an animal would stretch itself out lengthwise in an ‘upright’ posture and its mantle would darken. Often another animal observing this behavior would quickly swim away."
This behavior could be territorial, Chancellor explained, “but we still don’t really know much about octopus behavior. More research will be needed to determine what these actions might mean.”