The impact of introduced signal crayfishPacifastacus leniusculus on stream invertebrate communities

Abstract

ABSTRACT1. The effect of a newly introduced population of signal crayfish (Pacifastacus leniusculus) on a riverine invertebrate community in the River Clyde, Scotland, is examined. Five hypotheses related to crayfish impact on the invertebrate community are tested by comparing sites containing signal crayfish with similar sites in the same river which have not yet been colonized.2. The hypothesis that crayfish significantly reduce the total numbers of invertebrates in the community was supported by this study, with invertebrate density in areas containing signal crayfish around 60% of that with no observed crayfish.3. The hypothesis that crayfish presence affects some groups more than others was also supported. Plecoptera, Chironomidae, Diptera and Hirudinea, in particular, showed evidence of reduced species numbers in areas containing crayfish, and Plecoptera, Hirudinea, Tricladida and Hydracarina showed evidence of reduced densities. Community diversity and richness was also lower at sites containing crayfish.4. Neither the hypothesis that overall invertebrate biomass would be lower at sites with crayfish present nor the hypothesis that individual invertebrate size would be lower at sites with crayfish was supported.5. Overall the study indicates that introduced signal crayfish can significantly and fundamentally modify fluvial macroinvertebrate community structure.

Diel turbidity cycles in a headwater stream: evidence of nocturnal bioturbation?

“…These findings therefore support a growing body of research highlighting the detrimental impact of non-native signal crayfish on fluvial geochemistry, fluvial geomorphology and native aquatic biota (Crawford et al 2006;Johnson et al 2010;Harvey et al 2011). Their large size (typically 10-15 cm in length), aggressive nature, high population densities (up to 20 per square metre) and ability to rapidly colonise new environments have seen signal crayfish populations spread rapidly across Europe putting an increasing number of freshwater environments at risk (Holdich et al 2014;Kouba et al 2014).…”

Temporal variability in lotic macroinvertebrate communities associated with invasive signal crayfish (Pacifastacus leniusculus) activity levels and substrate character

“…Reduced taxa richness has also been documented in a number of other studies following signal crayfish invasion (e.g. Crawford et al 2006;Ruokonen et al 2014;Ercoli et al 2015a, b). When individual species were considered, the most widely cited taxa affected by crayfish invasion were the class of Hirudinea (leeches), which typically demonstrate significant reductions in abundance (Stenroth and Nyström 2003;Crawford et al 2006).…”

“…The effect of crayfish presence on invertebrate densities is highly variable with some studies indicating a reduction (Nyström 1999;Crawford et al 2006) whilst others have reported no differences (Lagrue et al 2014;Ercoli et al 2015a). The inconsistent results suggest that any effect on total community abundances is weak and probably a function of original community composition, and highly dependent on individual species responses.…”

“…Crawford et al 2006;Ruokonen et al 2014;Ercoli et al 2015a, b). When individual species were considered, the most widely cited taxa affected by crayfish invasion were the class of Hirudinea (leeches), which typically demonstrate significant reductions in abundance (Stenroth and Nyström 2003;Crawford et al 2006). The unprotected soft bodies and relative slow mobility of these taxa make them ideal prey items for crayfish (Stenroth and Nyström 2003).…”

A review of ecological interactions between crayfish and fish, indigenous and introduced

“…High populations and activity of signal crayfish may have negative impacts on resident fish. Signals directly predate on small fish such as stone loach and bullhead (Guan and Wiles, 1997), and on fish fry (Rubin and Svensson, 1993), while alteration of invertebrate communities (Crawford et al, 2006) and cropping of macrophytes by crayfish may put themselves and other denizens at risk (Lodge and Lorman, 1987;Hart, 1993, 1995;Matthews et al, 1993;Nyström and Strand, 1995). Studies have shown that predatory fish interfere with crayfish survival, activity and food consumption, e.g.…”