Peixes como sentinelas da urbanização: integridade biótica e microplásticos em riachos de Lavras na bacia do Ribeirão Vermelho (MG)

Abstract

Urbanization imposes multiple stressors on low-order streams, impairing their ecological integrity through physical, chemical, and biological alterations, a set of responses collectively known as the urban stream syndrome. This dissertation assessed the effects of urbanization on streams in the Ribeirão Vermelho basin, in Lavras, Minas Gerais, Brazil, from a temporal perspective, resampling in 2024 the 16 urban streams originally studied in 2018, using comparable methods to examine changes over a six-year interval. The first paper examined the biotic integrity of these streams based on fish assemblages, applying a multimetric index (MMI) composed of six metrics related to taxonomic composition, trophic guilds, and the dominance of tolerant species. Across the study, 8,218 individuals belonging to 13 species were recorded, with a strong dominance of Poecilia reticulata (94.4% in 2018 and 97.8% in 2024). No significant differences between sampling periods were detected for species richness, total abundance, or MMI scores, nor were changes observed in assemblage composition (PERMANOVA, p = 0.439) or multivariate dispersion (PERMDISP, p = 0.783). Spatial heterogeneity among streams was the dominant signal in both years, with the coexistence of reaches showing complete fauna retraction, reaches hyperdominated by P. reticulata, and reaches retaining residual native species such as Trichomycterus spp. and Characiformes. The second paper investigated microplastic ingestion by P. reticulata in 12 of these streams through analysis of the gastrointestinal tract contents of 240 individuals sampled in 2018 and 2024. Microplastics were recorded in all streams and in both periods, with a predominance of fibers and transparent and blue particles. A generalized linear mixed model (GLMM) detected no significant effect of period, sex, or body size on ingestion, but revealed strong spatial heterogeneity among streams, with consistent differences in the number of particles ingested per individual across reaches. Taken together, the results indicate that urban streams in Lavras remain under chronic ecological degradation, with low biotic integrity and continuous exposure to emerging contaminants, despite gradual improvements in municipal sanitation infrastructure. The recovery of these systems requires integrated interventions combining sanitation, urban stormwater management, and habitat restoration at the watershed scale