A newly developed dispersal capacity metric indicates succession of benthic invertebrates in restored rivers

Dispersal capacity plays a fundamental role in riverine benthic invertebrates’ colonization of new habitats that emerge following flash floods or restoration. However, an appropriate measure of dispersal capacity for benthic invertebrates is still lacking. Dispersal of benthic invertebrates occurs mainly during the aquatic (larvae) and aerial (adult) life stages, and each can be further subdivided into active and passive modes. Based on these totally four dispersal modes, we firstly developed a simple metric to estimate dispersal capacity for 528 benthic invertebrate taxa by incorporating weight for each mode. Secondly we tested this metric using benthic invertebrate community data from a) 23 restored river sites all involving an improvement of river bottom habitats dating back 1 to 10 years, b) 23 unrestored sites, and c) 298 adjacent surrounding sites in the low mountain and lowland areas of Germany. We hypothesize that our metric will reflect the temporal succession process of benthic invertebrate communities colonizing the restored sites, while no temporal changes are expected in the unrestored and surrounding sites. By applying our metric to these three river treatment categories, we found that the average dispersal capacity of benthic invertebrate communities in the restored sites decreased significantly within the early years following restoration, while there were no changes in both unrestored and surrounding sites. After dividing all taxa into quartiles representing weak to strong dispersers, this pattern became even more obvious; strong dispersers colonized the restored sites during the first year after restoration and then significantly decreased over time, while weak dispersers continuously increased. The successful application of our metric to river restoration might be promising to further apply this metric for example in river assessments or meta-community structure.