Macrophytes shape the functional diversity of zooplankton in Lake Iberá, Iberá Wetlands (Argentina)

Introduction: Aquatic macrophytes structure zooplankton communities by increasing habitat complexity and resource availability. This study evaluated the effect of macrophyte presence on the taxonomic and functional structure of zooplankton communities in Lake Iberá (Iberá National Park, Argentina). Methods: Zooplankton was sampled in October 2025 at four sites: two with macrophytes (WM) and two without macrophytes (NM). At each site, 100 L of water were filtered through a 58-μm plankton net, and samples were preserved in 4% formaldehyde. Organisms were identified and characterized using five functional traits. Presence–absence and species-by-trait matrices were constructed for analysis. Results: A total of 26 taxa were recorded, including 13 shared between habitats, two exclusive to NM, and 11 exclusive to WM. Taxonomic richness was higher in WM (24 taxa) than in NM (15 taxa). Rotifers showed the strongest response, increasing from seven to 17 taxa, whereas cladocerans and copepods exhibited similar richness. Alpha diversity indices (species richness, Shannon, and Simpson) were consistently higher in WM. Beta diversity was moderate (βSOR = 0.333) and mainly explained by nestedness (βSNE = 0.200), indicating that NM communities largely represented a subset of those in WM. Both habitats were dominated by filter feeders (>82%) and herbivore-detritivores (>45%); however, WM included all trophic groups and habitat categories, with greater representation of predators and scrapers. Functional diversity indices also revealed higher functional dispersion (FDis = 3.895) and Rao's Q (15.706) in WM, whereas FEve was similar between habitats. Conclusion: Habitats with macrophytes exhibited higher taxonomic richness and functional diversity than habitats without macrophytes. Greater structural complexity was associated with a broader functional spectrum, including all trophic groups and habitat categories and a higher proportion of crawling and sessile organisms. These findings highlight the key role of macrophytes in shaping the taxonomic and functional structure of zooplankton communities in subtropical wetlands.