Aquatic Invasions (2014) Volume 9, Issue 4: 529–535 doi: http://dx.doi.org/10.3391/ai.2014.9.4.11 © 2014 The Author(s). Journal compilation © 2014 REABIC Open Access 529 Research Article The Ponto-Caspian quagga mussel, Dreissena rostriformis bugensis (Andrusov, 1897), invades Great Britain David C. Aldridge 1 *, Samantha Ho 2 and Elsa Froufe 3 1 Aquatic Ecology Group, Department of Zoology, University of Cambridge, Downing Street, Cambridge CB2 3EK, UK 2 Environment Agency, Apollo Court, 2 Bishops Square Business Park, Hatfield A110 9EX, UK 3 Aquatic Ecology and Evolution Group, CIMAR/CIIMAR, University of Porto, 4050-123 Porto, Portugal E-mail: d.aldridge@zoo.cam.ac.uk (DCA), Samantha.Ho@environment-agency.gov.uk (SH), elsafroufe@gmail.com (EF) *Corresponding author Received: 28 October 2014 / Accepted: 19 November 2014 / Published online: xx 2014 Handling editor: Frances Lucy Abstract Great Britain has been subject to an increasing rate of invasion from freshwater species of Ponto-Caspian origin. A recent horizon-scan of potential invaders into Great Britain named the Ponto Caspian quagga mussel, Dreissena rostriformis bugensis (Andrusov, 1897), as the non-native species least wanted. On 29 th September 2014 quagga mussels were discovered in the Wraysbury River, Surrey, during a routine kick sample collected by the Environment Agency. Identity was confirmed using genetic markers (Cytochrome Oxidase I - COI) on five individuals encompassing a broad morphological variation. The absence of very large individuals (max. length 16 mm), absence of shells and absence of quagga mussels in samples collected during March 2014 point toward a recent invasion. The quagga mussels were found attached to submerged rocks, vegetation, bridge walls and shells of zebra mussels, Dreissena polymorpha (Pallas, 1771). The collection site is a small (<5m wide), shallow (<50cm deep) stream that is not navigable or regularly fished. This suggests that the species is more widely distributed than the current location, because such a system is unlikely to be the point of introduction. The shallow depth (30cm) in open water at which quagga mussels were abundant is surprising given that zebra mussels have failed to establish in such habitats, despite being present in the catchment for over 100 years. Previously published models predict quagga mussels will establish widely across England, western and southern Wales and central Scotland. The high abundance and inter-connectivity of waterways adjacent to the Wraysbury River suggest further spread is likely. Containment through national biosecurity measures (e.g. ‘Check, Clean, Dry’ of boats and equipment, as promoted by the UK Environment Agency) is recommended, although ultimately it can be assumed that quagga mussels will cause similar widespread ecological and economic harm in Britain as has been experienced in invaded regions of Western Europe and North America. Key words: dreissenind, invasive, zebra mussel, Wraysbury, alien, non-native, first record Introduction In recent years, there has been a dramatic spread of Ponto-Caspian species into Western Europe. This spread has been facilitated by the construction of canals which have linked different river systems. Canal construction has not only provided improved trade routes but has also created a number of invasion corridors from east to west (Bij de Vaate et al. 2002). Many of these new species have driven major ecological changes and caused considerable economic harm. The predominance of facilitative and commensal interactions between Ponto-Caspian species heightens their invasive potential and threatens to drive an ‘invasional meltdown’ (Gallardo and Aldridge 2014). Recent studies suggest that The Netherlands contains over 20 Ponto-Caspian freshwater species that have yet to be found in Great Britain (Gallardo and Aldridge 2013a). One of the species of greatest concern to Britain’s freshwaters is the quagga mussel, Dreissena rostriformis bugensis (Andrusov, 1897), which was identified as the species that posed the greatest risk to Britain’s biodiversity in a recent multi-taxon, multi- ecosystem horizon scan (Roy et al. 2014). Until the early twenty-first century the quagga mussel was a slower invader than the congeneric Ponto- Caspian zebra mussel Dreissena polymorpha (Pallas, 1771), a species that already costs Britain approximately £5 million per year (Oreska and Aldridge 2011) and threatens native biota (Aldridge et al. 2004; Sousa et al. 2010, Sousa et al. 2011).