Invertebrate Communities Associated with a Native (Vallisneria americana) and an Alien ( Trapa natans Macrophyte in a Large River

Macroinvertebrate fauna of native and alien macrophyte stands in the freshwater tidal area of the Hudson River, NY, were compared. The Eurasian water chestnut (Trapa natans has become widely established and abundant in the river. Beds of the native Vallisneria have been partly displaced by Trapa. Environmental differences between adjoining beds of Trapa and Vallisneria are considered in terms of oxygen concentrations, fish predation, and water circulation. Macroinvertebrate densities were higher in Trapa than in Vallisneria, probably because of greater plant biomass in Trapa beds. Epiphytic and benthic macroinvertebrates both differed between plant bed types, and also changed seasonally. Cladocerans collected from Trapa areas had a higher hemoglobin content than those from Vallisneria areas had. The gradual replacement of Vallisneria by Trapa may have increased aquatic system biodiversity. While there may be more food for fish in Trapa areas, the low oxygen concentrations may limit fish exploitation of this resource.