Assessment of fish community and food web structure in a restored stream within an ecological park; positive change in diversity with ecological management challenges

When evaluating the success of a stream restoration, it is pivotal to assess its ecological functionality as a sustainable habitat. In this study, we investigated fish communities across three sites with distinct structural features and environmental conditions in an urban restored stream located near the lower part of a major river. We analyzed the α- and β-diversity of fish communities and estimated the restored stream's contribution to the river's fish diversity. We also examined ecological niche space and niche overlap among fish species using carbon and nitrogen stable isotope analysis. Results revealed that the restored stream increased overall diversity and β-diversity in the region. Additionally, food web structure analysis showed variation in fish food source diversity among sites and species, resulting in diverse ecological niche areas and forms. The structural heterogeneity of the restored stream influenced fish feeding habits. However, many tolerant and invasive species were observed, with the invasive species Lepomis macrochirus markedly influencing competitive relationships with other fishes through its broad ecological niche area and overlap. These results emphasize the need to prioritize indigenous or non-native species establishment during stream restoration. Overall, our study highlights the important role of restored streams in increasing catchment fish diversity. Nevertheless, food web-centric monitoring and management strategies are necessary to effectively sustain local diversity.