‘Killer shrimps’, dangerous experiments and misguided introductions; how freshwater shrimp (Crustacea: Amphipoda) invasions threaten biological water quality monitoring in the British Isles

In 2010, the 'killer shrimp' Dikerogammarus villosus (Crustacea: Amphipoda) invaded the British Isles.  Past research from central Europe has shown this eastern European shrimp invader to be a 'voracious omnivore', highly predatory of a wide range of freshwater macroinvertebrate taxa and also fish fry.  It can become 'super-abundant' within invaded sites, greatly dominating native assemblages in terms of numbers and biomass.  Although the vast majority of past research has focused on the negative impacts of D. villosus invasion on native biodiversity, we consider the usually overlooked implications for biological water quality monitoring and ecological assessment.  We show how past invasions of other freshwater shrimp in the British Isles, such as Gammarus pulex and Crangonyx pseudogracilis, have undermined the ability of biotic indices to reliably reflect changes in water quality.  Within such invasions, more pollution tolerant invaders can replace more sensitive natives and invaders can be highly predatory of other macroinvertebrate taxa which contribute to biotic indices.  We predict the impacts of the D. villosus invasion will be greater than any previous shrimp invasion of the British Isles and indeed potentially of any other freshwater macroinvertebrate invasion thus far.  As it spreads throughout the British Isles, we predict this species will have drastic deleterious impacts on native macroinvertebrate assemblages, especially in its preferred rocky/stony habitats.  We consider ways forward for future biological water quality monitoring and ecological assessment within D. villosus invaded watercourses