Beyond Biodiversity Hotspots: Free-Flowing Tributaries as Ecological Refugia and Benchmarks for River Conservation and Sustainable Basin Governance

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Abstract
Empirical evidence integrating multiple biological levels on freshwater biodiversity persistence in regulated river basins remains scarce for Neotropical systems. We evaluated fish assemblage structure, reproductive strategies, and life-cycle support for migratory species across lotic and lentic habitats in three tributaries of the Porto Primavera Reservoir, Upper Paraná basin, Brazil, over a 12-year monitoring period (2007–2018), encompassing 104 species and a Life-cycle Support Index (LSI) based on occurrence of eggs, larvae, juveniles, and adults. Marginal lagoons functioned as biodiversity hotspots, with higher richness and diversity than river channels; reproductive guilds were habitat-partitioned, with opportunistic and parental-care strategists in lentic environments and periodic/migratory strategists in lotic habitats. Tributary identity was the strongest predictor of assemblage composition: the Aguapeí River, partially protected, showed the highest LSI values, whereas the Verde River provided the strongest evidence of reproduction for conservation-priority taxa, including the critically endangered Brycon orbignyanus, whose adults occurred exclusively there, and the vulnerable Pseudoplatystoma corruscans, for which adults, eggs, and larvae co-occurred. Three proposed hydropower developments on the Verde River would fragment a 200-km free-flowing stretch, threatening these conditions. Undammed tributaries are irreplaceable for freshwater biodiversity and should be recognized as conservation priorities in hydropower licensing and basin governance.
Funding Information
  • Companhia Energética de São Paulo

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