MACROINVERTEBRATES IN THE MAIN CHANNEL OF THE MISSISSIPPI RIVER NEAR CAPE 
GIRARDEAU, MO.

Juliann M. Battle, John K. Jackson, and Bernard W. Sweeney
Stroud Water Research Center, Avondale, PA 19311.

The Upper Mississippi River at Cape Girardeau, MO is considered the Open River 
reach that has remained relatively unimpounded.  In main channel at this 
location there are two major habitats, fine bottom substrates and rocks 
associated with wing dikes and stabilized banks.  We collected aquatic 
macroinvertebrates from fine sediments and rocks at four separate dikes between 
river miles 66-71.  Fine sediments were sampled using a Petite Ponar dredge 
during the fall of 1999, 2000, and 2002.  Rocks were sampled using artificial 
substrates (i.e., rock baskets) during the fall of 1999 and 2001.  In the fine 
sediments, a total of 60 taxa were collected during the three sample years.  
Most of these taxa were insects including 12 EPT (Ephemeroptera, Plecoptera, 
Trichoptera) taxa and 32 Diptera taxa.  Total macroinvertebrate density in the 
fine sediments ranged from 3737 individuals/m2 in 2002 to 8706 individuals/m2 in 
2000.  Oligochaete worms represented 77-92% of the total numbers.  Ephemeroptera 
(primarily Hexagenia) and Diptera (primarily chironomid midges) were the 
dominant insects collected.  The dominant functional feeding group (FFG) in the 
fine sediments was collector-gatherers  (93% of the total numbers), primarily 
oligochaetes.   On the rocks, a total of 50 macroinvertebrate taxa were found in 
1999 and 2001.  Most (80%) of these taxa were insects, including 21 EPT taxa and 
18 Diptera taxa.  Total macroinvertebrate density ranged from 3611-10,185 
individuals/rock basket with aquatic insects (mainly hydropsychid caddisflies) 
comprising >99% of the macroinvertebrates collected.  Total macroinvertebrate 
density on the rocks was generally 2-3 times greater in 2001 than in 1999, and 
this difference reflects increased density of hydropsychid caddisflies.  The 
dominant FFG on the rocks was collector-filterers, which comprised >95% of the 
total density.  There were 34 taxa that occurred in the fine sediments but not 
on the rocks, and 22 of the 34 were the dipterans no-see-ums and midges.   
Conversely, there were 20 taxa that occurred on the rocks but not in the fine 
sediments, and many of these taxa were mayflies and stoneflies.  Differences in 
assemblages between habitats appear to reflect flow and substrates.  The fine 
sediment assemblage was dominated by burrowing insects that prefer low flow, 
while the rock assemblage was dominated by taxa requiring fast current.

Keywords: macroinvertebrates, substrates, dikes, functional feeding group, 
Mississippi River