Abstract
Several species of invasive crayfish have become established in the Netherlands, the most recent addition being Orconectes virilis. Since crayfish are known to impact water quality and aquatic macrophytes in areas they invade, this study investigated whether this was also the case for this species under Dutch conditions and if so, whether a crayfish density producing “no effects” could be established. We focussed on the potential impact of O. virilis on water quality variables (pH, electrical conductivity, dissolved oxygen and turbidity), as well as their impact on submerged and emergent macrophytes. In a compartment experiment with different densities of O. virilis, statistically significant effects were observed at crayfish densities of 1.25 crayfish/m2 on electrical conductivity, turbidity, submersed macrophyte biomass, and the emergent plant Sagittaria sagittifolia, due to crayfish actively severing plants and physically disturbing the sediment. No statistically significant differences with controls were observed at a density of 0.63 crayfish/m2. Since densities of 0.03 to 5 crayfish/m2 have been found in different water types in the Netherlands, this indicates that the water quality and macrophyte biomass in Dutch waters are being negatively impacted by invasive crayfish. As a consequence, attempts to reach a good ecological status as required in the Water Framework Directive will be frustrated by the presence of this invader.
Highlights
Biological invasions are recognized as one of the most significant changes in the environment (Sala et al 2000)
This can lead to situations where invasive species dominate the aquatic community, as has happened with water hyacinth (Eichhornia crassipes, (Mart.) Solms, 1883) and the red swamp crayfish (Procambarus clarki, Girard, 1852) in Southern Europe (Holdich and Pöckl 2007; SoutyGrosset et al 2016), or floating marsh-pennywort (Hydrocotyle ranunculoides L. f.), Chinese mitten crab (Eriocheir sinensis Milne-Edwards, 1854), red swamp crayfish and musk rats (Ondatra zibethicus Linnaeus, 1766) in North-Western Europe (Bos and Ydenberg 2011; Paulissen and Verdonschot 2007)
Crayfish were not weighed after collection, but the fact that most individuals had lost their tie-wraps was considered a sign of moulting, and of growth
Summary
Biological invasions are recognized as one of the most significant changes in the environment (Sala et al 2000). Crayfish can alter the structure of aquatic ecosystems via their behaviour and polytrophic omnivorous diet, one of the most dramatic impacts being that on aquatic macrophytes (Cronin et al 2002; Feminella and Resh 1989; Lodge et al 2012; Rodriguez et al 2003; Rodriguez et al 2005; Twarlochleb et al 2013). Such changes can lead to alterations in water quality and to increased turbidity and nutrient loads (Angler et al 2001). Crayfish act as ecosystem engineers (Nyström et al 1996)
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