About Austrominius modestus (Darwin, 1854)
Austrominius modestus is a pearly grey, semi-translucent barnacle. It has four distinct plates, and leans slightly to one side. This species originated in Australia. It was first recorded in British waters at Chichester Harbour during the Second World War, and is thought to have arrived either attached to ship hulls, or via its larval stages carried in ship bilge water. It is now very common across southern England and Wales, and is spreading northwards; its spread may be limited by sea temperature. By 1960, it had reached the Scottish Borders, and it reached Shetland by 1978. It can be found on Atlantic coasts of Europe ranging from Gibraltar to Germany. It occupies the upper middle shore, is tolerant of the low salinity conditions found where fresh water enters the sea, and avoids exposed locations. Austrominius modestus is a suspension feeder. It uses feathery appendages that beat rhythmically to pull plankton and other organic particles into its shell to eat. Eggs develop into nauplius larvae that are released into phytoplankton; these larvae then mature into cyprid larvae, which eventually settle and cement themselves to rocky substrates. In the British Isles, A. modestus competes with Semibalanus balanoides, while in southern Europe it also competes with Chthamalus species. It is particularly successful as an invasive species because it grows quickly, tolerates reduced salinity, has a lower temperature tolerance than Chthamalus species and a higher temperature tolerance than Balanus species. It also threatens native species because it reaches maturity in its first growing season and can produce multiple broods of larvae each year. It occupies an extended habitat range, growing both high on the shore and in the neritic zone.
