Fish community responses and the temporal dynamics of recovery following river habitat restorations in Europe

Abstract

Considerable uncertainty exists regarding the ability of reach-scale habitat restorations to promote ecological integrity and affect community composition in degraded streams and rivers and the time scales at which these effects take place. Restoration of habitats on the reach scale (hundreds of meters to a few kilometers) is expected to support threatened species because many of them are habitat specialists. In contrast, generalist species are predicted to be replaced in restored reaches. We used a large data set for 62 reach-scale restoration projects in 51 stream systems in Germany, Switzerland, and Liechtenstein and analyzed the changes in fish community composition induced by the restorations in terms of species richness, species turnover, Brillouin diversity index, total fish abundance, and proportion of alien and endangered species. We further analyzed the temporal dynamics of the fish community recovery over a period of 19 y postrestoration. Species richness and Brillouin diversity index increased in most of the restoration projects (66 and 57%, respectively), but recovery to historical reference conditions was not achieved. Total abundance was enhanced by most of the projects. Species composition in restored reaches underwent directed shifts for at least 10 y, with high and variable species turnover in the first years that decreased over time. The effects of restoration on Brillouin diversity index were highly variable in the first few years after restoration, but tended to increase over time. These dynamics must be considered more carefully in future protocols for evaluating restoration results, and final evaluation of restoration outcomes on fish communities should not be made too early. Our results indicate that reach-scale habitat restorations may be a suitable tool for increasing local fish abundance and slightly enhancing species diversity. However, more targeted approaches are needed to support threatened species and repress alien species.

Mechanistic modelling for predicting the effects of restoration, invasion and pollution on benthic macroinvertebrate communities in rivers

“…Recent empirical models predicted the richness and total abundance of alien species invasions after restoring connectivity in a large river floodplain (Paillex et al, 2015), and the increase in alien species was pronounced within the first few years after restoration. Evidence of recolonisation by alien species was also reported after the restoration of the Rhine River (Simons et al, 2001), whereas for fishes Thomas et al (2015) found no indication that alien species particularly bene- Those native taxa that were predicted to occur without the presence of alien species, but were predicted to be absent in the presence of alien species, were further regarded as affected by the presence of alien species. In our study, we underlined that a high number of native taxa can be affected by the presence of alien species (i.e.…”

Does River Restoration Increase Fish Abundance and Survival or Concentrate Fish? The Effects of Project Scale, Location, and Fish Life History

“…However, because restoration of short reaches (<1 km) is often not sufficient to allow for dynamic rejuvenation of a variety of habitat types or to provide habitat for all life stages, Schmutz et al (2016) recommended that restoration should focus on dynamic, selfsustaining habitat improvement over several kilometers. In studies examining 24 and 62 European river restoration projects, respectively, Haase et al (2013) and Thomas et al (2015) found no correlation between a project's linear length and fish response or fish community composition. Muhar et al (2016) synthesized the results of these and other European studies and concluded that restoration response did not increase with project size.…”

“…() and Thomas et al. () found no correlation between a project's linear length and fish response or fish community composition. Muhar et al.…”

“…Species with high dispersal and colonization abilities have been reported to respond most positively to river restoration techniques (Thomas et al. ). Moreover, there is evidence that the ability of many non‐salmonids to colonize habitat is dependent on their presence in nearby pools and on within‐reach movement (Sundermann et al.…”

“…They found no effect of project size on the response of fish, benthic invertebrates, or aquatic macrophytes. Thomas et al 2015 Examined fish community response at 62 reach-scale restoration projects throughout Europe. The authors found no relationship between the length of the restoration project and fish community response.…”