Seasonal zooplankton dynamics in main channel and backwater habitats of the Upper Mississippi River

Abstract

This study used stratified random sampling to examine the spatial and temporal distribution of zooplankton communities in a large floodplain river (Mississippi River, USA). Potential mechanisms controlling zooplankton abundance and community structure were considered. Main channel and backwater habitats included in this study differed between a turbid upper pool reach where aquatic macrophytes were sparse and a lower pool reach which was considerably less turbid and had extensive aquatic macrophyte coverage. Samples were collected monthly during the summer over a 2-year period and multivariate analysis was used to examine the spatial and temporal distribution of zooplankton. Significant differences were found in zooplankton density and community composition among habitats and reaches within the pool. Rotifers were the dominant taxa and seasonality was pronounced, with peak densities often occurring in late-spring. Community structure varied by habitat and reach, which suggests that water quality, physical habitat characteristics, presence of aquatic macrophytes, and zooplankton sources can all influence the zooplankton communities of the Upper Mississippi River. Characterization of the zooplankton communities provides a basis for understanding changes in the river ecosystem and examination of zooplankton communities among habitats provides insight into the mechanisms affecting zooplankton dynamics.