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Small and impoverished regional species pools constrain colonisation of restored river reaches by fishes

Authors

  • STEFAN STOLL,

    1. Department of River Ecology and Conservation, Biodiversity and Climate Research Centre & Senckenberg Research Institute and Natural History Museum Frankfurt, Gelnhausen, Germany
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  • ANDREA SUNDERMANN,

    1. Department of River Ecology and Conservation, Biodiversity and Climate Research Centre & Senckenberg Research Institute and Natural History Museum Frankfurt, Gelnhausen, Germany
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  • ARMIN W. LORENZ,

    1. Department of Aquatic Ecology, Faculty of Biology, University of Duisburg-Essen, Essen, Germany
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  • JOCHEM KAIL,

    1. Department 4 Biology and Ecology of Fishes, Leibniz-Institut for Freshwater Ecology and Inland Fisheries, Berlin, Germany
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  • PETER HAASE

    1. Department of River Ecology and Conservation, Biodiversity and Climate Research Centre & Senckenberg Research Institute and Natural History Museum Frankfurt, Gelnhausen, Germany
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Stefan Stoll, Department of River Ecology and Conservation, Biodiversity and Climate Research Centre & Senckenberg Research Institute and Natural History Museum Frankfurt, Clamecystr. 12, 63571 Gelnhausen, Germany. E-mail: stefan.stoll@senckenberg.de

Summary

1. Using an extensive data set from 18 river restoration projects in the lower mountain ranges of Germany and 5462 river reaches in their surroundings, we estimated the spatial extent of the regional fish species pool from which restored river reaches are colonised.

2. Restoration resulted in a marginally significant increase in fish species richness; however, restored reaches still deviated markedly from natural reference conditions. Nearly all (96.6%) species occurring in restored reaches were present in reaches within a distance of 5 km up- or downstream of the restored reach.

3. Species richness in restored reaches was correlated with species richness within a 5-km species pool. This relationship was more pronounced for common than for rare fishes and applied to both the total number of fish species at the restored reach and the number of additional fish species that were not present at unrestored conditions.

4. The richness of the regional species pools was greatly impoverished. On average, only 50% of all species considered to represent natural reference assemblages were present. The limited success in establishing natural fish assemblages in restored reaches was attributed to spatial limitation (e.g. due to fragmentation) and an impoverished regional species pools from which restored reaches recruit.

5. We recommend that integrated river restoration management should consider not only the abiotic prerequisites of successful restorations, but also the structure and quality of the regional species pool.

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