Spatiotemporal variation in the taxonomic and functional structure of Cladocera along a subtropical channel in southern Brazil

Aquatic communities play a fundamental role in freshwater ecosystems, acting in energy transfer and nutrient cycling in the food chain. Among these communities, Cladocera often stand out due to their high abundance and ecological importance. This study evaluated the spatiotemporal variation of the Cladocera community along a channel located in the subtropical coastal plain (São Gonçalo Channel, southern Brazil), integrating taxonomic and functional approaches. This ecosystem connects two large water bodies in Brazil: Lagoa Mirim to the south and Lagoa dos Patos to the northeast. Sampling was conducted between 2018 and 2019 along a 42-km transect. A total of 133 sites were sampled across four annual periods in three zones of the channel, testing the following hypotheses: (i) the southern region of the channel presents higher taxonomic and functional diversity; (ii) the taxonomic and functional diversity metrics of the community are influenced more strongly by temporal variation than by spatial variation. Taxonomic diversity was measured using metrics of abundance, richness, taxon frequency, diversity, dominance, and evenness, while functional diversity was assessed through trait categorization and indices of functional richness, divergence, and evenness. A total of 2307 individuals of Cladocera were recorded, distributed across 16 genera, with Moina and Bosmina being the most frequent. The results showed that temporal variation was the main structuring factor of the functional and taxonomic composition of the Cladocera community. The findings of this study reinforce the importance of integrated approaches to understand the ecological processes structuring aquatic communities in subtropical water bodies.