Gloomy octopuses are not as loners as most people believe. Marine biologists found an underwater city where 15 of these creatures, also known as common Sydney octopuses, are engaged in complex social behaviors. Living in Jervis Bay, off Eastern Australia, the cephalopods communicate, mate, dwell together and evict each other from dens, according to a paper published in the journal Marine and Freshwater Behavior and Physiology.

Oclantis lies about 15 meters under the surface, is four meters wide and about 18 meters in length.

Image credit: John Turnbull /
Image credit: John Turnbull /

By recording 10 hours of video, researchers discovered how these octopuses live together. The scientists observed that the creatures usually are within an arm’s reach of each other and exhibit aggressive behavior, which the study authors are still unable to explain.

“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,” explained study co-author Stephanie Chancellor, as reported by Quartz.

Scientifically known as octopus tetricus, the sea animals experience a complex social behavior as a result of natural selection, as lead author David Scheel told Quartz. A professor of Alaska Pacific University, he explained that the gloomy octopuses behave similarly to vertebrates, which indicates that evolution may produce very similar results in different groups of organisms as long as the right conditions occur. This contradicts the theory that octopuses always live a solitary life and only interact with one another to mate once a year.

Scheel added that such congregations are likely to emerge in zones where food is plentiful, and shelter exists only in small patches of habitat. Still, he believes that unusual social behavior among octopuses has been discovered as a result of the improved ability to observe them. Nowadays, divers can rely on more advanced technology and can immediately share findings with scientists. This suggests that interactions between cephalopods may have existed for a long time.

There are rock outcroppings in Oclantis. A doctoral student in biological sciences at the University of Illinois-Chicago, Chancellor, explained that octopuses living there had built up piles of shells left over from their prey, especially clams and scallops. She said she considered the gloomy octopuses “true environmental engineers” since they sculpted the shell piles to make dens, as reported by Russia Today.

Researchers observed octopuses evicting others from those dens. There were 13 dens occupied and ten vacant.

The second city of octopuses found in a decade

Even though it has unique characteristics, Oclantis is not the only underwater city where octopuses have been found interacting with each other. Also in Jervis Bay, scientists found in 2009 a site they named Octopolis, an area 33 to 49 feet under the water’s surface where cephalopods formed a community.

The main difference between those sites is that Octopolis was known for a human artifact possibly made of metal that was heavily encrusted and had formed a central point later surrounded with dens created by octopuses. The unidentified object was about 30 cm long.

At the time, scientists believed the object was the reason why the cephalopods were attracted to the site, which has been observed for seven years now. Oclantis shows evidence that these creatures may have been socializing for a long time.

Source: Quartz