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Forget about a hole in the bottom of the sea, this octopus has found a hole in the beach. All octopuses have gills, so they require water to breathe. However, some octopuses can leave the water for brief periods to go foraging or crawling between tide pools. Yet, slithering into a gaping black hole on the beach is another story. This post from accuweather shows an octopus determinedly making its way to the hole, but why is it there, and where does it go?
The Long-Arm Octopus
The video above is said to have been filmed in Fujian province, China, which has the largest mudflat in the country. The octopus species is most likely Callistoctopus minor, previously known as Octopus minor. It is also commonly called the long-arm octopus or the Korean common octopus. This grey-colored octopus is found in coastal regions of northeast Asia, including China, Japan, and Korea. They are a benthic littoral species, which means they prefer the bottom sediment of nearshore areas where sunlight can penetrate. Their primary habitat is mudflats that form in tidal regions as mud and silt are deposited in natural harbors or estuaries.
The typical mantle of the long-arm octopus only reaches around four inches. Its total length is around 27.5 inches. It also has thinner arms compared to other octopus species. Despite its relatively small size, it doesn’t seem like this octopus should be able to fit into such a tiny hole. Although octopuses are muscular, they don’t have any bones. The only hard part in their bodies is their hooked, parrot-like beaks. Their beaks are primarily made of chitin, which is what lobster, crab, and insect exoskeletons are made of. So, as long as the beak fits, the rest of the octopus can also squeeze through.
Why Is There a Hole in the Beach?
It’s clear that the octopus in the video is intentionally heading for that opening. However, many of us are wondering why there is a hole in the beach in the first place. Octopuses are cephalopods, a group of ocean-dwelling mollusks. They have the most complex brains of any invertebrates, but most cephalopods have lost the outer shells of their ancestors. They now rely on their intelligence and other adaptations, such as camouflage, to avoid predators and competitors.
Yet many octopus species inhabit simpler coastal habitats where camouflage isn’t the most effective strategy. Coastal octopuses depend on some type of shelter for predator avoidance. It’s more common for octopuses to make dens in rocky crevices or among the coral underwater. However, a few octopus species dig their shelters in the seabed. So, the hole on the beach was probably made by the octopus in the video. Octopuses also sometimes take over abandoned shelters, regardless of the size of the previous occupant. The new owner then modifies the shelter to fit its proportions.
Octopus Architects
Scientists have recently discovered that the long-arm octopus digs extensive burrows under the mudflats. The octopus begins digging by sucking water into its mantle and shooting it out into the sediment. This creates a small depression it can stick its arms in to excavate a digging channel. When the channel is deep enough, it stretches out its long arms to dig a horizontal passage. Then it digs a vertical breathing channel, at the end of which is the breathing hole. The result is a sort of “U” shaped burrow with holes at either end.
With ventilation finalized, the octopus uses its water shooting action and its arms to wear down the inner walls of the horizontal passage. This creates what researchers call a “lounge” area, which is where the octopus spends most of its time. Once the burrow is complete, the octopus can inhale fresh ocean water from the digging hole, then expel the water and feces to the surface using the breathing hole. Scientists believe that as the octopus breathes, the lounge gradually expands to accommodate the size of a mantle full of fresh water. Long-arm octopuses leave the burrow to go foraging for crustaceans, especially at night. So, the octopus shown above is probably just headed home to relax after supper.
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