Subject:
The Bohol Discodoris (Discodoris boholiensis) is a relatively large nudibranch (up to 12cm/5 inches) that bears a striking resemblance to many different flatworm species, hence its alternative name; Flatworm Discodoris.
There are several distinctive characteristics of this nudibranch. Firstly, it can deceive potential predators by mimicking a flatworm in form, colouration, and locomotion. Secondly, it has the ability to autotomise parts of its mantle if attacked. Both of these features are effective defence mechanisms that enable the nudibranch to outsmart potential predators.
Mimicry, or the ability to imitate another organism or even an object, is a highly efficient anti-predation adaptation. Convincing a potential predator that you are something else is one of the most effective methods for avoiding predation. Many nudibranchs use mimicry as a means of deception and self-defence. In addition to flatworms, coral polyps, and sea cucumbers are also mimicked. Mimicry occurs in various forms and is extensively explained in our vlog post number 33 (see link below).
Autotomy is the ability to self-amputate body parts or appendages as a self-defence mechanism. Although it may sound strange to most people, there are well-known examples that most people will recognise; one of the best-known examples of autotomy is the lizard that sheds its tail when threatened. The lizard escapes, leaving behind only its wiggling tail. Most likely, the lizard will grow a new tail.
The Bohol Discodoris can shed parts of its mantle when attacked. These nudibranchs are often encountered by scuba divers, and underwater videographers and photographers frequently capture them with significant portions of their mantle edges missing, resembling a sea slug that has been bitten. Like the lizard, the Discodoris will gradually regenerate the missing tissue over time. For more examples of autotomy, visit our vlog post 15 (see link below).
The Bohol Discodoris also exhibits a peculiar behaviour; its locomotion speed varies depending on whether it is day or night. During nighttime, the nudibranch moves much slower than during the day. This behaviour is scientifically known as "photokinesis." While photokinesis is not fully understood, there are organisms that adjust their velocity based on light intensity. It is likely another form of defence against predators.
As a predator of sponges, its primary source of food, the Bohol Discodoris is widespread across Indo-Pacific waters, from the eastern coast of Africa in the Indian Ocean to the French islands of New Caledonia in the Pacific. Although this nudibranch is also active during daytime is more commonly encountered during night dives.
Technique:
To make the crawling slug more stand out, I used the usual tricks; sharpened the subject, increased the contrast slightly, blurred its surroundings and added a subtle vignette.
Nudibranchs are slow movers, and despite their incredible colour palette, they are often not very spectacular subjects in underwater videography. These animals are likely much better suited as photographic subjects. To maintain viewer engagement, I opted to keep this clip relatively short. One simple way to enhance interest for the viewer is by adding subtle sounds to the final product.
Filming location:
This short underwater videoclip has been filmed in Bali, Indonesia 🇮🇩
More about this topic:
For a in-depth description about mimicry please visit our vlog post 33 or click the following link: https://www.beyondscuba.com/post/a-juvenile-peacock-razorfish
and for a in-depth description about autotomy please visit our vlog post 15 or click the following link: https://www.beyondscuba.com/post/decoy-defence
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