There really are two famous octopus gathering sites off eastern Australia—but they are not cities in the human sense. Around Jervis Bay, researchers documented dense groups of Octopus tetricus living among discarded scallop shells. The sites, nicknamed Octopolis and Octlantis, are better understood as shell-bed neighborhoods created by the cumulative effects of feeding and denning.
There really are two famous octopus gathering sites off eastern Australia—but they are not cities in the human sense. In the waters around Jervis Bay, researchers found unusually dense groups of Octopus tetricus living in dens excavated among discarded scallop shells. The sites have been nicknamed Octopolis and Octlantis.
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The nickname is memorable, but it can also create the wrong impression. The octopuses did not plan streets, construct buildings, make fences, or design a settlement for their group. Instead, their ordinary activities—hunting, carrying food home, eating, digging dens, and handling shells—appear to have gradually created a shell-rich habitat that other octopuses could also use.
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Meet the octopuses of Jervis Bay
The animals involved are Octopus tetricus, commonly called the Common Sydney Octopus or Gloomy Octopus. This is a recognized species found in subtropical eastern Australia and northern New Zealand, not a newly discovered or mysterious animal.
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Like other octopuses, O. tetricus uses a lair or den for shelter. It feeds mainly on molluscs and crustaceans, including scallops and other shellfish. Octopuses often take prey back to a den, where eating can be safer than feeding in exposed surroundings.
That feeding habit is central to the story. Every meal can leave behind shells, and those shells can eventually change the seafloor around the den.
What are Octopolis and Octlantis?
Octopolis was the first high-density gathering site identified in the Jervis Bay area. A second site, later nicknamed Octlantis, was described in research published in 2017.
When Octlantis was discovered, researchers recorded 15 octopuses and several unoccupied dens. That number describes what was observed during the discovery period; it is not a permanent population estimate. Octopus numbers can change as animals arrive, leave, reproduce, find food, or face predators.
The second site included three rocky outcrops surrounded by an extensive bed of discarded scallop shells. The rocky features and accumulated shells provided more structure than the surrounding soft sediment, creating places where octopuses could excavate or occupy dens.
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The names “Octopolis” and “Octlantis” are informal nicknames popularized by media and researchers’ descriptions. “Underwater city” is a metaphor—not a scientific classification.
How an “octopus city” can emerge without a city planner
The most useful way to understand the sites is as a feedback loop:
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- It returns with food. Bringing prey back to a shelter allows the octopus to feed in a comparatively protected location.
- Empty shells accumulate. The remains form a midden—a concentrated pile or bed of discarded food remains.
- The shell bed changes the habitat. Shells can provide firmer, more complex material for digging or stabilizing additional dens than the surrounding sediment.
- More usable dens attract more octopuses. Those newcomers hunt and feed in the same area, adding more shells and reinforcing the habitat.
This is a case of individual engineering producing wider ecological effects. An individual octopus may intentionally excavate a den, maintain its entrance, move objects, or return with prey. But the large shell bed and the concentration of animals can emerge from the cumulative effects of many separate actions, without any evidence that the octopuses collectively planned the result.
Are octopuses really building anything?
That depends on what “building” means.
| Claim | What the evidence supports |
|---|---|
| Octopuses alter their surroundings | Yes. They excavate dens, handle shells and other objects, and leave discarded prey remains around their shelters. |
| Octopuses engineer habitat | Yes, in the ecological sense. Their repeated activities modify the seafloor and affect other organisms. |
| Octopuses planned a settlement | No evidence supports this interpretation. |
| Octopuses built buildings, roads, fences, or artworks | No. Those are sensational extensions of the story, not findings established by the research. |
| They built the entire site from nothing | No. The sites included natural rocky features, and one earlier site also involved a human-made object. The shell beds accumulated through repeated feeding and den use. |
Calling the octopuses “architects” can be playful, but it should not replace the more precise explanation: they are capable habitat modifiers, and their behavior can have community-level consequences.
A surprisingly social scene
The sites were also important because they challenged the simple image of octopuses as animals that are always solitary. At the dense gathering sites, researchers observed displays, arm probing, mating-related behavior, and attempts by octopuses to evict others from dens.
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Those observations show that O. tetricus can tolerate or actively engage with nearby individuals when local conditions make proximity worthwhile. Shelter, food availability, and predation risk may all help explain why several octopuses gathered in one place.
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But this does not mean the species is permanently social. Octopuses of this species are commonly observed alone around Sydney. The better conclusion is that their social behavior is flexible and context-dependent. When suitable dens are scarce or concentrated in one location, the benefits of remaining nearby may outweigh the costs of sharing space.
Why the shell beds matter to other animals
The octopuses are not the only animals affected by the altered habitat. Researchers reported invertebrates and fishes using or gathering around the shell-rich area. Larger predators may also be attracted by the concentration of prey and activity.
This is why scientists describe the octopuses as ecosystem engineers. An ecosystem engineer is an organism that physically changes its environment in ways that influence the conditions experienced by other organisms. Beavers are a familiar land-based example because dams reshape waterways. The octopus example is smaller and less deliberate at the landscape scale, but the principle is similar: animal behavior changes habitat, and that habitat change affects a wider community.
Importantly, “ecosystem engineer” does not imply foresight. The term describes the ecological effect, not a claim that the animal understands or intends every consequence of its actions.
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The most interesting lesson is not that octopuses recreated human urban planning. They did not. The lesson is that intelligence in another animal may appear in forms that do not resemble human institutions or technology.
These octopuses show flexible use of shelters and materials. They respond to nearby animals, compete for dens, interact during mating, and repeatedly modify the area around their homes. Their individual decisions can combine into a complex habitat that supports a concentrated community.
That distinction matters when interpreting animal behavior. A species does not need to create buildings, tools, or social institutions recognizable to people in order to demonstrate behavioral flexibility or ecological influence.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Can people visit the “octopus cities”?
The research places the sites in the Jervis Bay area, but that does not establish a current visitor-access policy or make the exact locations a public attraction. Readers should not assume that the sites can be freely visited, approached, collected from, or disturbed.
Anyone considering marine wildlife observation in the region should check current guidance from the relevant Australian marine, park, and local authorities, follow no-touch and no-collection practices, and avoid publicizing precise research-site locations without a responsible reason.
The real story behind Australia’s “underwater cities”
Octopolis and Octlantis are vivid names for unusual, dense octopus gathering sites—but they are not cities built through collective urban planning. They are shell-bed neighborhoods shaped by the accumulated effects of hunting, feeding, den excavation, and competition for shelter.
That explanation is more scientifically interesting than the headline. Individual octopuses appear to make practical choices about food and shelter, while the combined result is a modified habitat used by many animals. No central designer is required for a complex community to emerge.
Frequently Asked Questions
Did octopuses really build an underwater city?
No. Researchers did not find evidence of planned buildings, roads, fences, artworks, or a collectively designed settlement. The “city” label is an informal metaphor for a dense gathering site and altered shell-bed habitat.
What species lives at Octopolis and Octlantis?
The animals are Octopus tetricus, known as the Common Sydney Octopus or Gloomy Octopus. The species occurs in subtropical eastern Australia and northern New Zealand.
How did the octopus gathering sites form?
The sites formed through a likely feedback loop: octopuses carried prey to their dens, discarded shells accumulated, the shell bed made additional dens easier to create or stabilize, and more usable shelter attracted more octopuses.
Are these octopuses a social species?
They can gather and interact under suitable local conditions, but the species is not established as permanently social. Octopuses of this species are often observed alone elsewhere.
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The Bottom Line
Bottom line: The “underwater cities” near Australia are real gathering sites of Octopus tetricus, but the city is a metaphor. Repeated feeding and den-building created shell-rich habitat that encouraged more octopuses to gather and affected other marine life.
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