The common Sydney octopus, Octopus tetricus, also known as the gloomy octopus, inhabit the subtropical waters of New Zealand and eastern Australia. Prior to 2009 it was thought that these cephalopods are largely solitary and only meet up annually to mate. While this generally may be the case, researchers have found proof that this octopus sometimes congregate in small “cities”.
Led by Dr. David Scheel of Alaska Pacific University, researchers observed 15 octopus communicating and residing together in dens at a site they named “Octlantis” in Jervis Bay off eastern Australia. This behavior contradicts the solitary existence thought to be common for O. tetricus, as this is quite complex social behavior. Another gloomy octopus site was discovered back in 2009, named “Octopolis”, but at the time was considered an anomaly. This now begs the question whether these types of congregations are common.
Scientists believed the 2009 Octopolis site was the result of the octopus gathering around an unidentifiable man-made object, which they surrounded with dens. Since the discovery there could be between two and 16 octopuses there at any given time. However, at Octlantis there is no such object to explain the congregation. Apart from the mysterious object both sites where characteristically similar. Both were flat and featureless rocky sea floor outcroppings. Makeshift dens/middens were built from shells of the clam and scallop species they preyed upon.
Why the octopus congregate in these cities is still largely speculative. The gathering of multiple individuals leads to lots agonistic interactions, especially males, and as a feature on an otherwise featureless seafloor, attracts predators like sharks and rays.
Scheel believes the gloomy octopuses behavior likely hasn’t changed, but instead our ability to observe has improved. The technological advancements have allowed us to not only record more easily, but also communicate findings more freely. Still, cities like Octopolis and Octlantis may still not be very common and is probably limited to areas with areas where natural shelter is limited, but with plentiful food resources. The gloomy octopus isn’t the only other cephalopod thought to be solitary, but has been seen socially interacting. So what are the next questions we should be asking? Who makes up these groups? Are they kin? How could these aggregations affect fitness?
For more information on this study please the article in Marine and Freshwater Behavior and Physiology http://www.tandfonline.com/eprint/SuKqGmXPA8zJdrkjkSRE/full
