Octopuses are famous for their camouflage skills; however, they are also very good at hiding in shelters or dens. Apparently, each octopus has several dens to rest and feed in a certain area, within which they move in search of food. According to our experience working with octopuses, we have observed that each octopus has a couple of "main dens" in which they usually rest most
of the time and eat quietly after catching various preys. In addition, they have several "auxiliary dens" within its hunting area, which they use to take refuge from predators, hide while hunting or just relax.
All these dens can be found in cracks between or beneath rocks, holes in the sand, abandoned tires, cans or bottles, among others, and are easily recognizable (especially the "main dens") by the empty mollusc shells littering the doorway. The main entrance of these dens is usually surrounded by an accumulation of small stones, shells of dead bivalves and some exoskeletons of arthropods such as crabs or lobsters.
When a den is recent or is inhabited, the remains of shells are completely clean and do not present algae or other epibionts. However, when the shells are visibly accumulated in one place but covered by algae, it can be said that it is an ancient or abandoned lair. It could be thought that octopuses are somewhat disorganized when leaving the remains of their food right at the entrance of their "houses", or that it is not very intelligent to leave such an obvious signal that the den is occupied by an octopus, however, these remains are actually extremely useful when a predator approaches. We have witnessed that when an octopus feels observed, discovered or threatened inside its den, it hides quickly inside of it and collapses all the shells and rocks in the entrance, creating an immediate barrier against any attacker. This is recycling the "garbage" in a very intelligent and convenient way! This behaviour is especially useful on sandy bottoms where there are not many rocks to use as protection and the shells serve as a rigid and efficient barrier against any threat.
We know that the octopuses we seek in Balandra generally take refuge within bivalve shells, however, when exploring the site, we also found traces of dens under rocks and even in the sand with these characteristic traces. In this case, the shells belonged to very small bivalves (no more than 5 cm in length), so it is likely that they were consumed by the small octopuses that we are looking for.
We still have a lot to document in Balandra and much to discover about these experts in hiding. We hope to find more very soon and share more findings!
Originally posted on National Geographic Open Explorer to shelldwellingoctopuses.