The decorator crab is a member of the Majidae family, which is comprised of approximately 700 marine species with a triangular or occasionally rounded carapace covered by spines, hairs and knobs. This species is characterised by its ability to achieve excellent camouflage by taking fragments of soft corals, anemones, algae, sponges or hydroids from the surrounding environment and attaching them to the exoskeleton with a special gland secretion that hardens in seawater. The crab continues the process until it is sufficiently covered. The algae continue to grow once attached, helping the concealment. The legs can be very long in some species leading to the name “spider crab” by which they are otherwise known. Their legs aid in the selective placement of marine life onto the carapace and for foraging for small marine invertebrate prey.
The decorator crab are cream to yellow in colouration and have orange chelipeds with blue trim. They grow to a maximum carapace width of 4 centimetres. These crabs are usually found in sheltered, seagrass beds and on shallow rocky shores of the south-west Western Australia and around the southern coast to Victoria, including Tasmania. They occur to depths of 15 metres.
Other common names include: Spider crab
Occurrence at the Busselton Jetty:
So effective is the decorator crabs camouflage, this cryptic animal is very rarely seen. In the area surrounding the jetty, the species often attach pieces of telesto coral, a common soft coral species, which thrive by having a mobile existence for filter feeding. They tend to only be seen when moving from one location to another.
Image By: Busselton Jetty Inc.