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186. A Day Octopus is webbing or web-casting



Subject:

The Day Octopus (Octopus cyanea) is a fascinating creature known for its impressive webbing behaviour. Webbing refers to the sudden and remarkable display of the velum, a thin membrane that connects the octopus' arms. This extraordinary feature creates a visual effect akin to an open umbrella, captivating observers and providing insight into the octopus's hunting and defence strategies.


There are two primary motivations behind an octopus's decision to engage in webbing: hunting and self-defence. When the octopus uses its velum to hunt it’s called web-casting, when it does so to as self-defence it’s called webbing. As active hunters, octopuses target various crustaceans, particularly crabs. To effectively capture their elusive prey, octopuses must act swiftly, preventing their targets from escaping. With a quick and strategic manoeuvre, the octopus spreads its arms wide and encloses the prey within the velum, reminiscent of a skilled fisherman casting a net. By doing so, the octopus ensnares the crab, leaving it unable to escape, and ultimately delivers a precise bite using its sharp beak to penetrate the crustacean's sturdy carapace.


Apart from its role in hunting, webbing also serves as a formidable defence mechanism for the octopus. When faced with a threat, such as a predatory moray eel, the octopus instinctively employs its webbing as a defensive display. By flaring out its webbing, the octopus creates the illusion of a much larger size, aiming to intimidate and deter potential attackers. This tactic leverages the eel's natural instincts, making it think twice before pursuing the octopus. The webbing's dramatic expansion acts as a visual warning, signalling to the predator that engaging with the octopus could lead to a challenging encounter.


The intricate behaviour of webbing in the Day Octopus showcases the remarkable adaptability and intelligence of these cephalopods. Whether utilising webbing as a hunting technique or a defence mechanism, the octopus demonstrates its ability to exploit its physical attributes to maximise survival and optimise its chances of success. These creatures continue to intrigue scuba divers and underwater photographers and videographers alike, as they unravel the intricacies of octopus behaviour and further appreciate the wonders of the marine world.


Technique:

I was filming this octopus crawling on the base of a boulder when the animal suddenly spread its arms without warning or early notice, displaying its webbing. The webbing appeared to be exceptionally bright white for a split second, too bright for the camera's settings at that moment. To correct the nearly overexposed velum, I had to lower the contrast in post-production and darken the white area in the footage, which proved to be quite challenging.


Typically, I white balance whenever I change depth or when the lighting conditions change, but I was completely unprepared for the sudden emergence of the octopus's snow-white webbing. Had I known what was coming, I could have countered it by reducing my aperture to a higher f-stop or by lowering the camera's ISO.


Another way to address this excessive light is by activating your ND filter. Some cameras come with a built-in Neutral Density filter that can be easily switched on by flicking a switch.


Although this shot is not perfect, it captures an intriguing behaviour of marine life, and it is precisely these behaviours that make underwater videography fascinating.


Filming location:

This short underwater videoclip has been filmed in Mauritius 🇲🇺


More on this topic:

For other octopus insights please go to these vlog posts:


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