Contrasting Temporal Dynamics of Ostracod (Crustacea) Communities in Protected and Impacted Areas in a Brazilian Floodplain

Abstract

Environmental integrity is vital for the long‐term preservation of freshwater biodiversity, which is currently among the most threatened on Earth due to anthropogenic pressures such as dam construction. The present study investigated the temporal responses of ostracod communities over 8 years (2017–2024) in the Upper Paraná River floodplain, comparing a protected area (Ivinhema River) and a dam‐impacted area (Paraná River). We evaluated taxonomic and functional attributes including richness, abundance and composition, using Generalized Linear Mixed Models (GLMMs) and multivariate analyses. Results revealed contrasting dynamics: The protected area exhibited high temporal stability in abundance, functional richness and composition, with a slight richness increase correlated with electrical conductivity. Conversely, the dam‐impacted system showed significant temporal increases in species richness, abundance and functional richness, alongside significant taxonomic and functional reorganization. These shifts in the Paraná system were positively associated with dissolved oxygen levels, likely reflecting increased water transparency from upstream dams that promotes submerged macrophyte expansion and periphyton growth. The hatching of resistant egg banks and the influence of invasive species also contributed to these community changes. In conclusion, protected areas are effective at maintaining regional biodiversity stability and ecological integrity. Meanwhile, the impacted system demonstrates a trajectory of continuous community reorganization, highlighting how environmental stressors alter long‐term ecological dynamics. This research underscores the critical importance of long‐term ecological research for evaluating conservation policies.