First records in Great Britain of the invasive colonial ascidian Didemnum vexillum Kott, 2002

Abstract

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%