Subject:
A small Haig’s Porcelain Crab (Porcellanella haigae) is filtering plankton using its bristle-like collecting fans.
The Haig’s Porcelain Crab lives on Sea Pens (order Pennatulacea). These beautiful little crustaceans rely, just like the sea pen, on a constant flow of passing plankton as their main food source. Belonging to the family of porcelain crabs (Porcellanidae), they accomplish this by filter feeding using two relatively large collecting fans formed by bristle-like structures, called setae. These feeding appendages swing sideways alternately, unfolding and spreading the bristles or setae, akin to a child attempting to catch butterflies with a handheld net. They are capable of executing active sweeps to catch plankton with their collecting fans in stagnant or slowly flowing water, or by simply holding the collecting fans across the current when the speed of the nutrient-rich water is sufficiently high.
Sea pens are colonial invertebrate marine animals of the order Pennatulacea, class Anthozoa, and phylum Cnidaria. The animal is composed of a multitude of small polyps branching out of the main stalk connected to a root-like peduncle, which anchors itself into the substrate. These animals are capable of uprooting and relocating if the nutrient content carried by the current is insufficient. The sea pen catches its food with the tentacles at the end of each polyp. Sea pens can retract into the muddy or sandy bottom to avoid predation by sea stars and/or nudibranchs. They accomplish this by expelling water out of their body, deflating and retreating into their own peduncle rather than into the sand or substrate. They can also emit a glow in the dark. When conditions and stimuli are right, the sea pen can emit a bright-greenish light. There are more than 400 different species of sea pens, occurring in all saltwater habitats worldwide. Unfortunately, it was impossible to identify the exact species in this short underwater videoclip from the collected footage.
The sea pen has a symbiotic relationship with the porcelain crab. The crab defends the sea pen against predation from sea stars and nudibranchs by pinching the predator with its small but sharp claws. A well-aimed squeeze from the crab’s chela and dactyl is usually enough to scare away the predator. In return, the crab can live among the sea pen’s polyp branches and receives a much better position in the water column to catch its daily food.
Technique:
This footage is old, recorded in Bali more than 10 years ago. The sharpness of this short underwater videoclip is relatively low compared to the Sony 4K videocamera used these days. To enhance the quality of the clip, I used three different layers in post-production. The first and lowest layer is the original and colour-corrected footage. In the second layer, I masked out the background so that only the sea pen remained, to which I added a medium sharpness. On the third and upper layer, I once again added some sharpness, this time a little more intense, to bring out the little crab. Finally, I added a vignette mask.
Filming location:
This short underwater videoclip has been filmed in Bali, Indonesia 🇮🇩
More about this topic:
For a vlog post about another porcelain crab please visit our vlog post 183 or click the following link: https://www.beyondscuba.com/post/spotted-porcelain-crab-neopetrolisthes-maculatus
Watch it on YouTube:
You can watch it directly on YouTube by clicking the following link: https://www.youtube.com/watch?v=e5ZmSToZYo4
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