Southern Sand Octopus

Only a small number of cephalopods use the two behaviors burying and burrowing. Yes, there is a difference! Burying is considered the superficial covering with sediment while burrowing is the active movement through soft substrates where the substrate (like sand) is displaced and the surrounding substrate is often altered. 

In a sandy environment where there is no place to hide from predators this species creates a predator proof bunker! But, how do they do this? A team of scientists in 2015 reported the first detailed study of how the southern sand octopus burrows and how it can breathe while residing in this bunker.  The scientists observed octopuses burrowing in the wild and set up laboratory experiments to closely examine the burrowing mechanisms and if different sizes of sand (fine to medium, course, very course) influenced octopus burrowing.

Scientists created an “ant farm” style aquarium to see how this sand-dwelling octopus burrows and it turns out there are 4 stages for the southern sand octopus to create its burrow!

First, the octopus produces its own quicksand! Burrowing begins with the octopus directing its funnel downwards and fully expanding its mantle in preparation for expelling the first jet of water into the sediment. The jetting action of the mantle and siphon inject water into the sediment which temporarily suspends the sand grains in the water or “fluidizes” the sand grains. This increases burrowing effectiveness by reducing drag and the energy needed for burrowing.

Second, the octopus moves its arms in the quicksand while its mantle and funnel remain above the surface to continue the jetting action. Once the underlying sediment is fluidized, the octopus pulls the rest of its body under the surface!

Next, the octopus uses its arms and expanded mantle to push the surrounding sediment away from its body to burrow deeper. Scientists reported the octopus’s burrow ranged from 3-11 cm (1-4 in) from the surface and octopuses burrowed slowest in very coarse sediment because the larger grain size likely requires more effort in fluidization.

After burrowing deeper, the octopus extends two arms to the surface to create a ventilation chimney! Finally, the arms are retracted and there is one last strong exhalation that pushes any loose sand from the chimney. To maintain the burrows structure, the octopus lines the chimney with mucus! 

It is also possible that the females release a pheromone (sexually-attractive chemical) out of their burrow’s chimney! Groups of males have been observed swarming over a single female. Females lay large eggs (9-11mm or ½ in long) that they attach singly to hard surfaces. Once the large young hatch, they are immediately benthic and head into the sand. 

This burrowing octopus species provides insight into the possible ecology of other sand-dwelling octopuses whose burying or burrowing behaviors have yet to be explored!