As its name suggests, the gloomy octopus doesn’t tend to be the life of the party. The octopus (Octopus tetricus) tends to keep to itself and avoids interactions with other octopuses unless mating. During the day, they retreat into their dens, which they often block with rocks. But a new study published is upending our understanding of these creatures. In findings reported in the journal Marine and Freshwater Behaviour and Physiology, scientists observed a site off the coast of Australia where 15 gloomy octopuses communicated and lived together. The site has been dubbed “Octlantis.”
The researchers captured mating, signs of aggression, chasing, and other signaling behavior on their video footage. “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,” said Stephanie Chancellor, a Ph.D. student in biological sciences at the University of Illinois and an author of the paper.
This is the second time a community of gloomy octopuses has been found. The first site was found in 2009 in Jervis Bay, off the east coast of Australia, and nicknamed Octopolis. However, scientists saw that community as an outlier, since it was built around a small, possibly metallic man-made structure. (Jervis Bay seems to be a veritable hotspot for animal interactions—it was also here that researchers found that sharks may establish long-term relationships with other sharks that can last for years.)
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This time around however, all elements of the community—a few hundred meters away from the first site—are natural. Octlantis is about 10 to 15 meters under the water’s surface, about 18 meters long, and four meters wide. It is made up of patches of exposed rock and beds of discarded shells from animals the octopuses ate. Scientists found a total of 23 dens there—13 of which were occupied. The dens consisted of holes excavated into sand or shell piles.
“At both sites, there were features that we think may have made the congregation possible—namely several seafloor rock outcroppings dotting an otherwise flat and featureless area,” said Stephanie Chancellor, a Ph.D. student in biological sciences at the University of Illinois and an author of the paper. “In addition to the rock outcroppings, octopuses who had been inhabiting the area had built up piles of shells left over from creatures they ate, most notably clams and scallops. These shell piles, or middens, were further sculpted to create dens, making these octopuses true environmental engineers.”
In addition to observing the habitat, the researchers also observed interactions among the octopuses via video over an eight-day period. “Animals were often pretty close to each other, often within arm’s reach,” said Chancellor.
“These behaviors are the product of natural selection, and may be remarkably similar to vertebrate complex social behavior,” said David Scheel, from Alaska Pacific University. “This suggests when the right conditions occur, evolution may produce very similar outcomes in diverse groups of organisms.”
The scientists aren’t sure what causes the aggressive octopus behavior, but they posited it may be linked to living in densely-populated areas. However, Chancellor said, “we still don’t really know much about octopus behavior. More research will be needed to determine what these actions might mean.”