Purple barnacles are a flat, grey barnacle with four wall plates and a diamond shaped orifice. They have a granular, scaly appearance, representing a volcano. The species is relatively uncommon on open rock surfaces, but is abundant in shaded habitats away from the direct force of the waves where it remains moist during low-tide. They grow up to 25 millimetres in diameter and 8 millimetres in height.
Barnacle larvae are free swimming and resemble the larvae of other crustaceans. As the barnacle larvae mature, they settle head first on a suitable surface, such as timbers at the top of the piles. Their head ‘cements’ on to the hard surface, their jointed legs become modified feathery feeding tentacles known as “cirri”, and their external skeleton becomes a series of hard plates that surround the body. Purple barnacles are filter feeders in moderate currents, and feed by flicking out the cirri through the plates, sifting plankton from the water column before drawing them back inside the shell to the mouth. Water is also drawn in during this process to prevent desiccation during exposure at low tide.
Barnacles are hermaphroditic, whereby they possess both male and female reproductive organs. Barnacles have the longest penis of any animal in relation to its body size, the penis extends out through the top of the shell in search for a nearby mate to exchange sperm. This is an evolutionary trait designed to maximise the abundance of the species. Barnacles often form clusters, however if they are separated by some distance they do have the ability to self fertilise.
The purple barnacle is distributed from Kalbarri, WA to Moreton Bay, Qld and around Tasmania.
Occurrence at the Busselton Jetty:
The purple barnacle is one of the early colonisers of the jetty piles and occur in abundance with the giant rock barnacle.