Characterizing fish responses to a river restoration over 21 years based on species' traits.

Understanding restoration effectiveness is often impaired by a lack of high-quality, long-term monitoring data and, to date, few researchers have used species' trait information to gain insight into the processes that drive the reaction of fish communities to restoration. We examined fish-community responses with a highly resolved data set from 21 consecutive years of electrofishing (4 years prerestoration and 17 years postrestoration) at multiple restored and unrestored reaches from a river restoration project on the Lippe River, Germany. Fish abundance peaked in the third year after the restoration; abundance was 6 times higher than before the restoration. After 5-7 years, species richness and abundance stabilized at 2 and 3.5 times higher levels relative to the prerestoration level, respectively. However, interannual variability of species richness and abundance remained considerable, illustrating the challenge of reliably assessing restoration outcomes based on data from individual samplings, especially in the first years following restoration. Life-history and reproduction-related traits best explained differences in species' responses to restoration. Opportunistic short-lived species with early female maturity and multiple spawning runs per year exhibited the strongest increase in abundance, which reflected their ability to rapidly colonize new habitats. These often small-bodied and fusiform fishes typically live in dynamic and ephemeral instream and floodplain areas that river-habitat restorations often aim to create, and in this case their increases in abundance indicated successful restoration. Our results suggest that a greater consideration of species' traits may enhance the causal understanding of community processes and the coupling of restoration to functional ecology. Trait-based assessments of restoration outcomes would furthermore allow for easier transfer of knowledge across biogeographic borders than studies based on taxonomy.

The effect of lateral connectedness on the taxonomic and functional structure of fish communities in a lowland river floodplain.

In river floodplains many conservation programs focus on the main river channel as the richest in species. Lateral floodplain waterbodies, which contribute largely to functional processes in river systems, often remain overlooked and exposed to anthropogenic pressures. Although the role of hydrological connectedness between lateral waterbodies and the main river on taxonomic composition of fish communities is well understood, effects on functional community composition is much less studied. Abundance data of fish communities were gathered from 152 electrofishing sites in the main channel and lateral floodplain waterbodies of the river Lippe (Germany), over 18 years. These data were used to compare taxonomic, functional, conservation and recreational fishing aspects along the floodplain lateral connectedness gradient. Fish species richness decreased along the lateral continuum from the main river channel to isolated floodplain waterbodies. In contrast, the relative abundance of endangered and also of non-native species increased along this gradient, highlighting the ecological and conservational importance of floodplain waterbodies. Species composition in floodplain waterbodies differed across the connectedness gradient showing distinct assemblages which were not merely subsets of the main channel. The variability of life-history and feeding strategists among classes of lateral connectedness confirmed the importance of each connectivity class in contributing to the overall floodplain functional diversity. This study highlights the need of preserving fish taxonomic and functional biodiversity across the floodplain as one integrated hydrosystem. Conservation and restoration measures should therefore extend to include the whole floodplain area and the complete spectrum of differently connected floodplain waterbodies in addition to the main channel of the river.