摘要：The colonial ascidian Didemnum vexillum was observed overgrowing fouling organisms present on structures within Holyhead Marina in North Wales in September 2008. Despite the examination of 9 other marinas in Wales during December 2008 and February 2009 no further populations were found. During December 2008 the extent of D. vexillum within Holyhead Marina and the surrounding harbour area was examined by diving. D. vexillum formed dispersed colonies throughout the marina, with <1% to 10% cover, but was not observed at any location within Holyhead harbour outside of the marina. Levels of infestation appeared to be low indicating a recent possible arrival. D. vexillum was found on the hulls of two vessels berthed within Holyhead marina but these vessels were long-term residents and not believed to be the source of infection. However, it is expected that hull fouling on recreational boats may become important vectors in the dispersal of D. vexillum to other regions around Britain. Although the species has been known in northern Europe since the 1990s, this is the first recorded established population of D. vexillum in Great Britain. In September 2008 a single colony of D. vexillum was collected in a marina in Plymouth and a colony, appearing to be D. vexillum, was photographed at the Darthaven Marina in 2005. The species was confirmed at this site in July 2009 by the collection of a single colony.
