The zooplankton community structure within a river is governed by a variety of physical, chemical, and environmental features.  The current study assessed the role of flow in characterizing the zooplankton community of the Missouri River (length 4,180 km, discharge 2,256 m³/s).  Missouri River zooplankton samples and physico-chemical variables were collected from 78 sites over a 2,831 km range by collaborating EMAP field crews during July–September 2005.  We identified rotifers to genus, and cladocerans and copepods to species.  We analyzed these samples to test for differences in community structure between hydrologically-distinct flow variability units.

Results/Conclusions

Identifications revealed 30 species of cladocerans, 22 species of copepods, and 27 genera of rotifers from the Missouri River.  The results of this study indicate there are detectable differences in zooplankton community structure among flow units.  Distance from the nearest upstream reservoir explained more of the overall community pattern of the river than any other combination of environmental factors, reflecting an indirect influence of flow and alteration of the river on the zooplankton community of the Missouri River.  This study suggests that before zooplankton can be used as bioindicators of other environmental stresses, hydrology must first be taken into account.