Divers, look out for gloomy octopus cities

Octopuses are usually thought of as solitary, mingling with others only to mate, but social interactions between them could be more widespread than previously recognised, say marine biologists who have been studying them in Australia.

They have been observing a colony of gloomy octopuses (Octopus tetricus) living on a rock outcrop at the sort of high densities only ever once observed before – at a site nearby.

The new site, dubbed Octatlantis by the scientists, is in Jervis Bay on Australia's east coast, and while filming on eight separate days they saw it typically occupied by between 10 and 15 octopuses.

The team recorded frequent complex social interactions between the animals, including signalling, mating, evicting one another from their sand-and-shell dens and attempting to expel individuals from the site altogether – giving the community the flavour of a violent frontier town.

The only other such site previously studied had been “Octopolis” in 2009, also in Jervis Bay at a depth of 17m. Because that site seemed to have grown up around a small unidentifiable man-made artefact, its circumstances had been thought unique.

There was no such focal point at Octatlantis, which lies between 10 and 15m deep and measures 18 by 4m, so the scientists speculate that the rocks themselves, sticking up on an otherwise featureless seabed, must have been the attraction.

“We plan to continue to explore and study these sites as well as other habitat,” Divernet was told by Professor David Scheel of Alaska Pacific University, co-author of the report.

“We would be delighted to hear from divers who may have encountered similar situations in their underwater explorations. We wouldn’t know about these sites if it weren’t for the dive community.”

The research is published in Marine and Freshwater Behaviour and Physiology Journal here


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