LATERAL DISTRIBUTION OF UNIONID MUSSELS IN SHALLOW CHANNEL 
BORDER HABITAT OF POOL 19, MISSISSIPPI RIVER

Jeffrey M. Stepping, Richard V. Anderson, and Benjamin G. Kirgan
Department of Biological Sciences, Western Illinois University, Macomb, IL  61455

Many shallow channel border habitats of the upper Mississippi River have low density 
mussel populations.  These populations are important since they may serve as the source 
of colonizers to reestablish depleted mussel beds.  Density and distribution patterns of the 
mussel population in a shallow channel border habitat at RM 378 in Pool 19, Mississippi 
River, was quantitatively sampled during the summer of 2004 and 2005.  Mussels were 
sampled every 5 m along a 135 m transect positioned from the shoreline toward the 
navigation channel.  Mean density at the site was 27.8 mussels per m2.  Peak densities 
and diversities occurred between 20 and 60 m from the shoreline in approximately 1 m of 
water.  Lowest densities were in the wave washed areas 5 to 10 m from the shoreline.  
Some species specific distribution patterns were observed.  Pimplebacks, threeridges, and 
fragile papershells were all more abundant within 60m of the shoreline.  Other shallow 
channel border sites exhibited similar distribution patterns, although mean density varied 
significantly between sites from a low of .9 to a high of 27.8 per m2.  Some mussels 
species were collected from all channel border sites sampled.  Zebra mussel infestation 
levels were low in these habitats during the sampling period with fewer than 10% of the 
mussels carrying a mean of just over 1 zebra mussel per shell.  The channel border 
habitat is important to the maintenance of mussel communities in this riverine system.

Keywords:  Unionid mussels, channel border habitat, Mississippi River, distance from 
shoreline