Hydro-climatic changes promote shifts in zooplankton composition and diversity in wetlands of the Lower Paraná River Delta

The Paraná River Delta is one of the most biodiverse and largest mosaic of wetland ecosystems in South America. Yet its natural hydrological patterns are being strongly distorted by sustained land use intensification and extraordinary severe droughts. Understanding whether the aforementioned processes negatively affect wetland biodiversity is urgently needed to delineate accurate conservation actions. In this study we analyzed zooplankton diversity patterns at the local and regional scales, as well as compared species composition between natural (freshwater marshes) and artificial water bodies (ditches), all of them affected by livestock activities. Our study involved two hydro-meteorologically contrasting conditions within two consecutive years of sustained drought: a high water stage (HW) and a low water stage (LW). Adverse environmental conditions in the LW period enhanced local zooplankton abundance and taxonomic richness, but decreased beta diversity and individual biomass, leading to a simplification of functional diversity. Species composition differed between freshwater marshes and ditches; however, they equally contributed to the zooplankton diversity metrics, suggesting that both kinds of freshwaters acted as complementary contributors to regional zooplankton diversity. Considering the regional drought patterns occurring in this landscape, we expect a generalized biotic and functional homogenization of zooplankton wetland diversity in the very next few years.