Scientists have discovered a second site where gloomy octopuses interact with one another, debunking the popular belief that octopuses are solitary animals.
Octopuses are generally solitary animals that interact with one another only when mating.
However, those gloomy octopuses (Octopus tetricus) residing at a site off the eastern coast of Australia (off Sydney to New Zealand) have been observed interacting with one another—either directly (via den evictions) or indirectly (via posturing, chasing or colour changes).
Dubbed Octlantis, the site measures 18 metres long and four metres wide. It is at a depth of about 10 to 15 metres, and comprises several patches of exposed rock and beds of discarded shells from consumed prey. There are thirteen occupied and 10 unoccupied octopus dens there.
Judging from footage captured by four GoPro cameras situated at the site, about 10 to 15 octopuses were occupying the site. Mating, signs of aggression, chasing, and other signalling behaviours were observed.
“Animals were often pretty close to each other, often within arm's reach," said Stephanie Chancellor, a Ph.D. student in biological sciences at the University of Illinois at Chicago. She is also one of the authors of a paper on the subject, published in the Marine and Freshwater Behaviour and Physiology journal.
“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,” she said.
Such behaviour could be territorial, but Chancellor said that more research would be needed to determine what the actions mean.
This is the second site where this unusual behaviour has been observed. The first site is located in Jervis Bay, off the eastern coast of Australia, and named Octopolis. It comprised several dens as well as a flat, human-made object about 30 centimetres long.