ZOOPLANKTON OF THE UPPER MISSISSIPPI RIVER: SPATIAL PATTERNS OF COMMUNITY 
STRUCTURE AND THE INSHORE RETENTION CONCEPT

Alexander P. Levchuk1 and John H. Chick1

Illinois Natural History Survey, Great Rivers Field Station, Brighton, IL 62012

      Zooplankton in the Upper Mississippi River System (UMRS) are understudied 
relative to zooplankton in large lentic systems and even other large rivers.  
These understudied organisms are an important part of the biota of the UMRS, 
supporting an abundant and diverse zooplanktivorous fish community.  Using 
zooplankton samples collected as part of the United States Environmental 
Protection Agency’s Great Rivers Ecosystem Environmental Monitoring and 
Assessment Program, this study describes large-scale spatial patterns in 
zooplankton community structure and relates these patterns to environmental 
variables in the UMRS.  Zooplankton community structure in the UMRS varies by 
river reach (Upper, Lower, and Open River), with higher densities of crustacean 
zooplankton observed in the Upper Reaches.  The surface area of habitat 
features, thought to function as retention zones, above each sampling site was 
quantified using Aquatic Areas GIS data available from the Upper Midwest 
Environmental Sciences Center and combined with water quality data collected 
concurrently with zooplankton sampling.  Overall community structure was 
correlated with temperature, conductivity, and upstream retention zones.  
Rotifer community structure was only correlated with retention zones in the 
channel border, but crustacean community structure was correlated with retention 
zones in both the channel border and floodplain.  Community structure of 
cladocerans and rotifers was most correlated with upstream habitat features one 
day’s distance upstream; whereas, copepod community structure was most 
correlated with habitat features three days’ distance upstream.  In addition to 
correlating zooplankton community structure with inshore retention zones in the 
UMRS, this study represents the first attempt to determine the spatial scales at 
which the presence of upstream inshore retention zones affects zooplankton 
community structure and composition.  

Keywords: zooplankton, inshore retention, habitat composition, GRE-EMAP, GIS