Native and alien macroinvertebrate richness in a remnant of the former river Rhine : a source for recolonisation of restored habitats?

Rivers are among the most endangered ecosystems of the world with dramatically decreasing biodiversity. Rehabilitation programmes aiming at restoration of riverine ecosystems rely on the recolonisation of native macroinvertebrates from refuges. We examined whether a relatively natural remnant of the former river Rhine (Altrhein) harbours a higher richness of benthic macroinvertebrates than two sites of the modified Rhine with artificial and semi-natural embankments near Basel. All three sites were bimonthly sampled between May 2007 and May 2008 using three techniques: Kick and Sweep, drifting animals collected from pieces of stone turned by hand, and animals collected from stone surfaces. Taxa richness was higher in the Altrhein than in the two sampling sites in the river Rhine, but it was mainly a result of the large number of individuals sampled at this site. Despite 17% of taxa recorded were alien, the three sampling sites differed neither in the number of alien taxa nor in their abundances. However, lower percentages of both alien taxa and individuals were recorded in the Altrhein than at the other two sites in the Rhine. Indicator value analysis showed that the macroinvertebrate community of the Altrhein maintains several native and specific taxa. Multivariate analyses supported the separation of the communities collected at different sampling sites and also the uniqueness of the community in the Altrhein. The observed patterns, however, strongly depended on the sampling method applied, thereby calling the attention to the application of standard sampling methods and also to the restriction of result comparisons on projects using identical sampling methodology. Our study shows that the remnant of the former river Rhine serves as a refuge for macroinvertebrates which may facilitate future restoration of the river embankment.