Abstract
The Asian cyprinid Pseudorasbora parva is considered to be a major threat to native fish communities and listed as an invasive alien species of European Union concern. Our study aims to gain evidence-based knowledge on the impact of both P. parva and its parasite Sphaerothecum destruens on native fish populations by analysing fish assemblages and body condition of individuals of native fish species in floodplain water bodies that were invaded and uninvaded by P. parva. We explored the use of environmental DNA (eDNA) techniques to detect S. destruens. Prevalence of S. destruens in native fish species was assessed. Fish samplings showed significantly negative correlations between the abundance of P. parva and the native Leucaspius delineatus, and Pungitius pungitius and three biodiversity indices of the fish assemblages (Simpson’s diversity index, Shannon–Wiener index and evenness). Contrastingly, the abundances of the native Gasterosteus aculeatus and P. parva were positively related. In nearly all isolated water bodies with P. parva, this species is outnumbering native fish species. No effect of P. parva presence was found on body condition of native fish species. Sphaerothecum destruens was demonstrated to occur in both P. parva and G. aculeatus. Gasterosteus aculeatus is suggested to be an asymptomatic carrier that can aid the further spread of S. destruens. Analysis of eDNA proved to be a promising method for early detection of S. destruens, here showing that S. destruens presence coincided with P. parva presence. The ongoing invasion of both P. parva and S. destruens is predicted to pose a significant risk to native fish communities.
Highlights
Invasive species affect ecosystem functions and services (Vilaet al. 2010) and can have a high economic impact (Cook et al 2007)
We are addressing the following research questions: (1) how do fish assemblages differ in water bodies with or without P. parva in terms of abundance and reproductive success of native species and community diversity? (2) does P. parva presence have an effect on body condition of native fish? and (3) what is the prevalence of S. destruens in native fish species? As there is a need for quick and reliable methods to detect non-native pathogens, we address the following research question: (4) can environmental DNA be used as a molecular method to detect S. destruens in situ?
Pseudorasbora parva was found to be present at 21 sites (Fig. 1) and co-occurred with 14 other fish species: Abrama brama, Carassius auratus, Carassius gibelio, Cobitis taenia, Cyprinus carpio, G. aculeatus, Gobio gobio, L. delineatus, Neogobius melanostomus, Proterorhinus semilunaris, Pungitius pungitius, Rhodeus amarus, Scardinius erythrophthalmus and Tinca tinca (Online Resource 2)
Summary
Invasive species affect ecosystem functions and services (Vilaet al. 2010) and can have a high economic impact (Cook et al 2007). Threats caused by alien pathogens, often associated with other invasive species that serve as reservoirs, are poorly understood and deserve more attention in risk assessment and management of biological invasions (Roy et al 2017). Pathogen pollution caused by spill-over from invasive fish species goes largely undetected in ongoing monitoring schemes, clouding the causes of their detrimental effects on naıve native species (Andreou and Gozlan 2016). The cyprinid topmouth gudgeon (Pseudorasbora parva) and its associated pathogen Sphaerothecum destruens are an example of such a cryptic, invasive duo. Their invasion initially started via aquaculture trade (Sana et al 2017), with P. parva serving as an unaffected reservoir. There is a growing need for evidence-based knowledge on its impact and effective management measures
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