Subject:
Like a strange scavenger right out of a science fiction movie, the Blackspotted Sea Cucumber (Pearsonothuria graeffei) is collecting any detritus it encounters on its way with its sticking mouth pads. This continually foraging invertebrate is only active during daylight hours. At night, this Echinoderm becomes inactive, raising its rear end and retracting its tentacles into its mouth.
The Blackspotted Sea Cucumber scavenges the coral reefs and seabeds of the Indo-Pacific Oceans. It is seldom found deeper than 25m/82ft. It is quite often encountered by amateur divers and snorkelers as it occurs well within the diving limits of recreational scuba divers.
The Blackspotted Sea Cucumber has various ways of defending itself against predators.
Most sea cucumber species excrete a white sticky substance from their anus when harassed. This sticky substance, a cluster of fine spaghetti-like tubes called Cuvieran tubules, helps immobilise the aggressor who gets entangled in an array of sticky yarns. This gluey substance ensures a slow but safe retreat fro the sea cucumber. However, the Blackspotted Sea Cucumber employs this defence mechanism only as a last resort. The rarely excreted sticky Cuvieran tubules of the Blackspotted Sea Cucumber are believed to contain chemicals with pain-killing and cancer-curing abilities.
To deter potential predators, this sea cucumber prefers to use other defensive mechanisms. Firstly, the outer skin of this sea cucumber has a high concentration of toxins, making it also unsuitable for human consumption compared to other sea cucumbers. Secondly, as a juvenile, the Blackspotted Sea Cucumber employs a combination of defensive zoomimesis (resembling another animal) and aposematism (advertising its toxicity through colouration) by resembling in size, colour, and morphology the dorid nudibranch, Phyllidia varicosa. The brightly white, black, and yellow-coloured sea slug relies on aposematism and its toxicity as its form of defence. By resembling the nudibranch, it may trick predators into thinking it is a distasteful and toxic sea slug rather than a tasty sea cucumber.
Technique:
To showcase this peculiar marine invertebrate, I chose to film it head-on; the head is where all the action happens (the other end of the animal being its anus). The seemingly incessant slow march of tentacles feeding with sticky pads is likely the most active part of this sea cucumber, making it the most captivating activity for any underwater videographer to film and for viewers to watch. It's noteworthy that the path of the Blackspotted Sea Cucumber is unidirectional, meaning it cannot move backward. Understanding this can aid in positioning your underwater videocamera: the animal will confidently approach, steadily and continuously, toward the objective or dome of your underwater videocamera.
To further dramatise this close-up underwater shot, I've included a sound that, with a little imagination, could mimic the sea cucumber's constantly moving mouth pads collecting sediments and detritus. There are numerous sounds available for purchase and download from the internet, and while finding an exact match may not always be possible, with some creativity (thinking outside the box), you can find a sound that effectively accompanies your underwater video shot and sounds convincing to viewers.
Filming location:
This short underwater videoclip has been filmed in Bali, Indonesia 🇮🇩
More about this topic:
For other in-depth descriptions about the feeding sea cucumbers please visit vlog post number 79 or click https://www.beyondscuba.com/post/a-sea-cucumber-of-the-synaptidae-family
Watch it on YouTube:
You can watch it directly on YouTube by clicking the following link: https://www.youtube.com/watch?v=Ci-Ocv6wyck
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