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We regularly post short Marine Wildlife Videos an Photographs with a short explanation regarding the subject and the technique used to capture the image.

All videos are made by Olivier Van den Broeck using Light & Motion video lights

and all photographs are by Greet Meulepas unless stated otherwise.

152. Velcro- or Blunt crab (Camposcia retusa)

Subject: Living amongst coral rubble and seagrass beds, this slow-moving nocturnal Velcro Crab (Camposcia retusa) is, although quite common, very hard to spot.

It uses the hairs (setae) that cover its body to stick to pieces of rubble and snipped-off bits of sponges. These hairs are hooked, just like Velcro hook-and-loop fasteners, hence its name "Velcro Crab." These crabs use their claws (chelae) to collect different pieces of decorating material, usually sessile animals such as sponges, ascidians, and bryozoans or even plant-like lifeforms such as algae. The crab then cuts or tears these materials into pieces of suitable length and size. After which, it uses its mouth to soften the edges of the collected goods before sticking them against its densely with hooked hairs covered carapace and legs (pereiopods) to attach the gathered material. The sponges and other marine life forms attached by the crab will continue to grow, maintaining the crab's superb disguise. The Velcro Crab, a scavenger that feeds on dead organisms and decaying matter, also attaches excess food to its body to consume at a later time.

The decoration made by the crab out of distasteful sponges combined with stored decaying food serves not only as a near-perfect camouflage but also produces a very unpleasant taste, which deters the crab’s predators such as octopuses and groupers.

Velcro Crabs, like all crustaceans, moult to grow larger. When this happens, the crab takes off all the decorations from its old shell and attaches them to its new shell. Besides being an excellent form of camouflage and a deterrent for predators, the to its body attached growth also makes the crab look bigger, which in turn is an advantage in male-to-male competitions over a mate. The colour, size, and shape of the decoration do not affect the crab's attractiveness to their female counterparts. After mating, female Velcro Crabs carry the eggs under their abdomen until they hatch and become planktonic larvae. These larvae are carried by the ocean's currents until they are large enough to settle on one of the Indo-Pacific reefs. This wide distribution means that these crabs can have totally different looks in different parts of the ocean, depending on the available supply of decorating materials, as some sessile animals that these crabs use may be location-specific.

Technique: Music is extremely important in cinematography. It creates an atmosphere, enhances storytelling, and establishes the mood of the scene. Here, we have chosen a tune that adds some suspense to this video clip of a slowly crawling and alien-looking intriguing creature. During the daytime, these crabs sit almost motionless amongst small rubble and debris. Therefore, it is much better to film these cryptic crustaceans on night dives when they move around. Motionless creatures can make great photographic subjects but are far from ideal in video. When filming nocturnal creatures like the Velcro Crab, artificial lighting is necessary to illuminate the subject. This can be a tricky process, as the video light needs to be positioned in a way that doesn't disturb the natural behaviour of the creature.

Dive into the world of underwater videography with our online Marine Wildlife Videography course!