Life on the road: fish communities composition in roadside ditches of the Atlantic Forest

Temporary aquatic habitats are essential for maintaining regional fish diversity, especially in tropical ecosystems. However, artificial ephemeral environments such as roadside ditches remain largely overlooked in ecological research, despite their potential to support native, threatened and even invasive species. In this study, we first assess the fish community composition in roadside ditches of the Atlantic Forest, southeastern Brazil. These habitats exhibited extreme environmental conditions, including hypoxic waters, elevated temperature fluctuations and very acidic waters. Throughout the year, we recorded 17 fish species, including endangered and exotic taxa, across 36 ditches sampled in the Preto River microbasin. Species richness was higher during the Wet Period, likely due to increased hydrological connectivity with nearby streams. Although species richness was higher during the Wet Period, species composition did not differ between periods. Redundancy analysis revealed low explanation of environmental variables on community structure, while a significant positive correlation between spatial distance and community dissimilarity suggested dispersal limitation as a major structuring force. These findings highlight both the ecological relevance of artificial temporary habitats in fragmented landscapes and the requirement to integrate such environments into regional species inventories, especially as natural wetlands continue to decline.