First detection of a highly invasive freshwater amphipod (Crangonyx floridanus) in the United Kingdom

Abstract

The freshwater gammarid, Crangonyx floridanus, originates from North America but has invaded and subsequently spread rapidly throughout Japan. We provide here the first genetic and microscopic evidence that C. floridanus has now also reached the United Kingdom. We found this species in two locations separated by more than 200 km (Lake Windermere in the North of the UK and Smestow Brook, West Midlands). The current distribution of C. floridanus is currently unknown, however both sites are well connected to other river and channel systems therefore the chance of further spread is high. Genetic analyses of C. floridanus indicate that British inland waters are colonised by the same linage, which also has invaded Japan. We recommend further work to assess the distribution of this species and its impact on the local fauna and flora. KeywordsCrangonyx floridanus, first record, United Kingdom N; Longitude: -2.93880 W) and on 26 th September 2018 in the Smestow Brook, West Midlands (Latitude: 52.5727 N; Longitude: -2.2196 W). We present both microscopic and genetic evidence for the presence of C. floridanus in these habitats. Materials and methodsLake Windermere is the largest natural lake in England, with a maximal length of 18.08 km, a maximal width of 1.49 km, a maximal depth of 66 m and a surface area of 14.73 km 2 . Lake Windermere is protected as part of the Lake District National Park and the site is actively used for recreation and tourism. Moreover, a station of the British Freshwater Biological Association (FBA) is located close to Lake Windermere and provides facilities for research on the ecology and conservation of local species on the western shore of the lake.On the 11 th September 2017 and later, on the 28 th July 2018, kick sampling was undertaken as part of a routine monitoring approach. Crangonyx specimens were separated from the samples, preserved in absolute ethanol and transported to the University of Derby for genetic and microscopic analyses. In total, one individual was collected in 2017 and 11 more in 2018. On 26 th September 2018, two more Crangonyx specimens were found during kick sampling the submerged root structures of riparian vegetation in Smestow Brook, a small river more than 200 km away from Lake Windermere. Samples were again preserved in 100% ethanol. Light and Scanning Electron -Microscopy (SEM)Crangonyx specimens (n = 11) were placed on the glass of a Nikon Multiphot diascopic mount and lit by darkfield illumination using a tungsten halogen fibre optic light source. Pictures were taken with a Nikon D7000 mounted on the photomacrography stand, set to colour balance of 3200°K, with a 65mm macro lens (https://www.microscopyu.com/museum/multiphot-large-format-photomacrography-microscope).Samples for SEM were dehydrated in ethanol, placed on aluminium stubs and coated in gold using a splutter coater (Emitech K550X). Samples were then placed in a Vega 3 SEM (TESCAN)