Octopuses may be solitary creatures, but groups of the cephalopods are emerging from their hiding places off the coast of Australia where they are building intricate structures out of shells, according to a study in the journal Marine and Freshwater Behaviour and Physiology. Dubbed Octlantis, the tiny “village” of approximately 15 animals, formed over a number of generations, is believed to have been created in the absence of humans and is built around rocks with mounds of discarded shells and scavenged objects, such as beer bottles. However, as well as socialising and mating, the octopuses also evict other occupiers from homes and physically square up to each other putting themselves in danger from predators such as sharks.
https://arstechnica.com/science/2017/09/why-octopuses-are-building-small-cities-off-the-coast-of-australia/