Temporal Patterns and Drivers of Freshwater Fish Beta‐Diversity of Gravel Pit Lakes

Freshwater ecosystems are in the midst of a biodiversity crisis marked by non‐random and often dramatic shifts in fish community composition. Yet, the patterns and underlying ecological drivers of these community dynamics within gravel pit lakes—widespread artificial lakes with significant socioeconomic and ecological value—remain understudied. This study examines patterns and drivers of beta‐diversity of fish communities across 16 gravel pit lakes in southwestern France over 10 years. Our results unveiled strong shifts in fish community composition, with lake maturity (older and more productive) emerging as the main driver. Immature lakes experienced substantial species turnover over one decade, harbouring more unique fish communities, whereas mature lakes showed little change, contributing less to overall beta‐diversity. Highly invaded lakes displayed higher levels of species nestedness than species turnover compared with uninvaded lakes. The contributions of native and non‐native species to beta‐diversity remained relatively constant on average over the study period, although with some notable exceptions. Non‐native species such as common carp ( Cyprinus carpio ) and Wels catfish ( Silurus glanis ) had increasing contributions to beta‐diversity, whereas native European perch ( Perca fluviatilis ) and roach ( Rutilus rutilus ) were increasingly more common (i.e., widespread) despite declining biomass when present. A number of abiotic and biotic factors likely contributed to the diversity patterns observed. Eutrophication is associated with increasing turbidity and hypoxia/anoxia, promoting the dominance of more tolerant, largely non‐native, fish species. The higher proportion of species nestedness in invaded communities may stem from reduced invasibility or local extinctions over time. Finally, European perch, a pioneer species, exhibited increasing homogenisation of its biomass across lakes over the 10‐year period, resulting in similar small populations distributed throughout the study area. These findings highlight temporal changes in fish community composition within gravel pit lakes, revealing the complex interplay between lake maturity and non‐native species dynamics as major drivers.