BackgroundThe amphipod and microsporidian diversity in freshwaters of a heterogeneous urban region in Germany was assessed. Indigenous and non-indigenous host species provide an ideal framework to test general hypotheses on potentially new host-parasite interactions, parasite spillback and spillover in recently invaded urban freshwater communities.MethodsAmphipods were sampled in 17 smaller and larger streams belonging to catchments of the four major rivers in the Ruhr Metropolis (Emscher, Lippe, Ruhr, Rhine), including sites invaded and not invaded by non-indigenous amphipods. Species were identified morphologically (hosts only) and via DNA barcoding (hosts and parasites). Prevalence was obtained by newly designed parasite-specific PCR assays.ResultsThree indigenous and five non-indigenous amphipod species were detected. Gammarus pulex was further distinguished into three clades (C, D and E) and G. fossarum more precisely identified as type B. Ten microsporidian lineages were detected, including two new isolates (designated as Microsporidium sp. nov. RR1 and RR2). All microsporidians occurred in at least two different host clades or species. Seven genetically distinct microsporidians were present in non-invaded populations, six of those were also found in invaded assemblages. Only Cucumispora dikerogammari and Dictyocoela berillonum can be unambiguously considered as non-indigenous co-introduced parasites. Both were rare and were not observed in indigenous hosts. Overall, microsporidian prevalence ranged from 50 % (in G. roeselii and G. pulex C) to 73 % (G. fossarum) in indigenous and from 10 % (Dikerogammarus villosus) to 100 % (Echinogammarus trichiatus) in non-indigenous amphipods. The most common microsporidians belonged to the Dictyocoela duebenum- /D. muelleri- complex, found in both indigenous and non-indigenous hosts. Some haplotype clades were inclusive for a certain host lineage.ConclusionsThe Ruhr Metropolis harbours a high diversity of indigenous and non-indigenous amphipod and microsporidian species, and we found indications for an exchange of parasites between indigenous and non-indigenous hosts. No introduced microsporidians were found in indigenous hosts and prevalence of indigenous parasites in non-indigenous hosts was generally low. Therefore, no indication for parasite spillover or spillback was found. We conclude that non-indigenous microsporidians constitute only a minimal threat to the native amphipod fauna. However, this might change e.g. if C. dikerogammari adapts to indigenous amphipod species or if other hosts and parasites invade.Electronic supplementary materialThe online version of this article (doi:10.1186/s13071-015-1036-6) contains supplementary material, which is available to authorized users.

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1. The response of benthic invertebrate assemblages to stream restoration is the subject of numerous recent studies, but the process of recolonisation of restored river sections is still poorly understood. Field studies are often flawed by uncertainties about whether the observed species colonised the restored sections after restoration or whether they were present before restoration. 2. We investigated restored streams in the Boye catchment in an urbanised area in Germany. The streams were formerly open sewers and thus were not inhabitable by benthic invertebrates, except for Oligochaeta. Restoration included the construction of underground sewers for wastewater and morphological remodelling of the stream bed. 3. In the spring of 2012, we sampled seven restored former channels connected with near-natural upstream sections, which were never used as sewage channels and are in good status morphologically, and six unconnected restored former channels. Restoration measures had been conducted between one and 19 years before sampling. Additionally, we sampled 21 near-natural sites within the catchment and eleven near-natural sites in neighbouring catchments. Near-natural sites were considered to be potential source sites from which benthic invertebrates might colonise the restored sites. 4. We recorded 128 taxa and categorised them into five dispersal classes that reflect dispersal capabilities and degree of ecological specialisation. Assemblages at restored sites were characterised by lower numbers of taxa and/or high abundance of hololimnic taxa and poorly dispersing winged species and by higher species numbers and abundance of strongly dispersing generalists. 5. A distinct recolonisation sequence was derived from the observed patterns, in which winged, strongly dispersing generalists colonised most rapidly and were followed by hololimnic species, weakly dispersing generalists and habitat specialists. Restored sites connected with near-natural upstream sections were colonised more rapidly than unconnected restored sites, particularly by habitat specialists. Almost 90% of the recolonisation events originated from sources within a distance of 5 km. We observed a succession from pioneer assemblages to more mature communities, which resembles that of the surrounding near-natural sites. 6. In conclusion, assemblages in connected, restored sites needed nine to 19 years to reach maturation, while the settlement of assemblages in unconnected sites is expected to require more time.

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Measurement of restoration success is a challenge, especially in multiple-stressed urban systems. Standard indicators for ecological assessment may be too robust to indicate small but continuous improvements. Thus, a standardized method of the European Water Framework Directive (EU WFD) is extended by additional samplings of macroinvertebrates in the urban Emscher catchment. The aim is to prove whether additional sampling adds value to interpretate restoration success. According to the EU WFD, the Emscher's ecological status and potential are mainly identified as good to moderate regarding biological components of macrophytes and macroinvertebrates, whereas bad regarding fish communities. The additional sampling improves the quality of the biological dataset, because twice as many species of macroinvertebrates are found compared to the WFD method. Hence, the additional sampling allows a stronger indication for community ordination, and community metrics describing diversity, dispersal, and feeding preferences as well as by disentangling the roles of environmental variables. Nevertheless, it is concluded that the standardized and simple WFD method is sufficient to capture the most relevant effects. However, if the budget is allowed and information on the species pool, nature conservation, or aspects of early indication are needed, it may be useful to implement an additional sampling of macroinvertebrates.