Crab; Red Bait - Busselton Jetty
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Crab; Red Bait

 

Occurrence at the Busselton Jetty:  The red bait crab can be seen at any time of the day and occur in abundance on the piles of the Busselton Jetty.  They can be observed grooming themselves, and utilising old, uninhabited barnacle shells for shelter.  Most often they can be seen feeding upon sponge growth using their claws to delicately cut pieces off.  A pair of maxillipeds in front of the mouth help the jaws tear up and manipulate food before passing it through to the mouth.

Plagusia chabrus
Red Bait Crab

The red bait crab is a member of the family Grapsidae, or shore crabs, which are well adapted for life out of water and include nearly all crabs encountered on rocky shores.  The red bait crab differs from other grapsids by living subtidally on reefs rather than on intertidal shores.  The red bait crab is easily recognised by its large size, brightly coloured knobs dotted over the deep red to dark brown carapace especially around the head and legs, deeply indented teeth around the front of the body and the covering of dense hairs that extend in rows down the legs.  Similarly with all crabs, the first three pairs of thoracic appendages have been modified into mouthparts that hold and tear apart their prey, with the male having much larger claws than the female.  This species feed throughout the day and night, mainly on encrusting invertebrates such as bryozoans, sponges and hydroids.  Females brood their eggs under their small abdomen until they hatch.

Preferring moist environments, the red bait crab is found around the low-tide mark on the rocky shore and underwater to depths of about 8 m. It tends to hide among seaweed and under rock ledges and on jetty timbers.  This species is common in the temperate waters of southern Australia, from Rottnest Island, around the coast to New South Wales, and around Tasmania.  They are also found in New Zealand, South Africa and Chile.

As their name suggests, they are often caught and used for bait.  They are popular prey items for the western blue groper, morwongs and the buffalo bream.  They grow to a maximum carapace length of 7.5 centimetres.

Other common names include:  Red rock crab

References:

Edgar, G. (1997) Australian Marine Life: The Plants and Animals of Temperate Waters, Australia

Morrison, S., Storrie, A.  (1999)  Wonders of Western Waters.  Department of Conservation and Land Management, Western Australia

Morrison, S and P., Storrie, A.  (2003)  Beneath Busselton Jetty.   Department of Conservation and Land Management, Western Australia