Octopuses generally shun contact with other octopuses, preferring to spend most of their lives alone. But 50 feet below the waves in Australia's Jervis Bay, a group of octopuses is regularly seen together on a tiny patch of seabed. This hub of cephalopod social interaction has even been nicknamed by scientists: welcome to "Octopolis"!

The animals sometimes mate. Sometimes they fight. And sometimes they appear to hurl objects at each other – a surprising behaviour that's piqued the interest of animal behaviour researchers. 

“Very few animals have been reported to throw things at one another, so it would be significant if the octopuses are doing it,” suggests Peter Godfrey-Smith from the City University of New York in an interview with New Scientist.

 

Godfrey-Smith has been studying Octopolis together with marine biologist David Scheel of Alaska Pacific University since its discovery in 2009. They have learned that despite its small size – only a few square metres – Octopolis has become a much sought-after piece of ocean real estate for the local gloomy octopus (Octopus tetricus) population.

Octopolis itself is nothing more than a few thousand scallop shells and marine life covering a small structure that was probably originally metal. The shells appear to have been brought there by the octopuses themselves, and form the perfect substrate for digging out an octopus den.

There's just one problem: there isn’t enough space to go around for the small congregation trying to eke out a living here. As more shells are added by the octopuses, Octopolis is expanding – just not fast enough to accommodate everyone, it seems. The cramped quarters often lead to squabbles over territory. With their closest neighbours literally at arm’s length, “boxing” matches between Octopolis residents are a common sight.

"There seems to be a lot of fairly ornery behaviour which has to do with policing and guarding territory," Godfrey-Smith tells NPR.

Scientists first observed the object-throwing behaviour after setting up cameras to record the goings-on in Octopolis when divers weren’t around to disturb the local residents. In a recent presentation at a conference on animal behaviour in Cairns, Australia, Godfrey-Smith showed video footage of octopuses gathering debris in their arms before blasting it in the direction of their nearest rival with a powerful jet of water. Octopuses shoot jets of water from a fleshy siphon under their mantle to propel themselves through water, to clean debris out of their dens, or to scare off pesky intruders. But this is the first ever observation of them using these water-jets to launch objects at another octopus.

 

Scallop shells, it seems, have become projectile weapons in the war for Octopolis.

Scientists are still unsure if this debris-throwing behaviour is intentional. It could be that the octopuses are simply cleaning out their territory and accidentally spraying their neighbours. But if it is a case of the octopuses purposefully flinging objects at their rivals, it's one of only a handful of such cases observed in the animal kingdom. Many primate species hurl stones, sticks, logs and other objects at their enemies. Elephants have been seen throwing dung at each other and polar bears allegedly crush seals and walruses with the occasional well-aimed toss of a rock.

Of course, this complex shell-tossing behaviour won't be surprising news to octopus experts. The sequencing of the octopus genome recently gave us insight into the genetic origins of the creatures’ intelligence. Long before they were observed tossing shells at each other at Octopolis, the world had witnessed their ability to use conch shells as tools and harness their problem-solving skills to get themselves out of sticky situations.

How the residents of Octopolis hit upon using scallop shells as projectiles is an open question. Research has revealed that octopuses can learn behaviours by observing each other, so it's possible that social learning is at play here. But more research is needed for scientists to confirm whether or not the behaviour is intentional and exactly why it occurs.

In the meantime, the cameras are still rolling out in Jervis Bay. Just what the octopuses will do next as they battle for control of Octopolis is anybody’s guess.  

Video credits: Peter Godfrey-Smith (CUNY and University of Sydney), David Scheel (Alaska Pacific University), Stefan Linquist (University of Guelph) and Matthew Lawrence. Via NPR.

Top header image: John Turnbull, Flickr