Integrating taxonomic and functional indicators of fish communities for adaptive management of transitional ecosystems

Transitional environments in deltaic areas host diverse aquatic ecosystems with distinct communities and functions. This study evaluates the conservation value and ecosystem functioning of eight aquatic ecosystems in the Po River Delta Park, (Northwestern Adriatic, Italy) using fish communities as indicators based on presence/absence data. Seasonal patterns in species occurrences and functional traits related to habitat use and feeding mode were analyzed to assess ecological dynamics and their relationship with environmental factors. Multivariate analyses were applied to identify the main drivers of fish community composition and alpha and beta diversity metrics were quantified. Coastal lagoons exhibited the highest values of both taxonomic (up to 28 species per site) and functional richness (up to 12 unique trait combinations). Among the environmental variables water level regime (tidal vs. artificially regulated) and wetland surface area emerged as significant predictors, explaining up to 66.1% of the seasonal variation in both taxonomic and functional composition. Functional beta diversity analysis revealed the central role of migratory species, reinforcing the importance of wetlands as nurseries and feeding grounds. Seasonal functional shifts were also evident: detritivorous species contributed most to beta diversity in autumn and winter, while planktivorous species were more influential in spring and summer, reflecting seasonal trophic dynamics. These findings confirm the effectiveness of fish community structures as sensitive indicators and demonstrate the need for integrating taxonomic and functional approaches to improve wetland monitoring and management. Restoring more natural hydrological regimes in enclosed wetlands, particularly through adjusted water level management, could enhance biodiversity, strengthen ecological functions and increase resilience to environmental change. This supports adaptive management efforts and contributes to objectives of the EU Biodiversity Strategy for 2030.