INVERTEBRATE COMMUNITY STRUCTURE ON SNAGS IN MAIN CHANNEL AND SIDE CHANNEL 
HABITATS OF THE UPPER MISSISSIPPI RIVER

Beth Rycyzyn and Michael Delong.  Large River Studies Center, Biology 
Department, Winona State University, Winona, MN 55987.

Habitat assessment of large river ecosystems is of importance in evaluating the 
health of a river.  Large rivers are heterogeneous systems, which contain main 
and side channels, in addition to other types of habitats.   Main channel and 
side channels are both lotic habitats, but exhibit many physical and chemical 
differences.  For example, the main channel is deep and wide, which may produce 
higher current velocity.  Side channels are shallow and narrow, with generally 
lower current velocities.  Physical and chemical differences have the potential 
to create biological differences between main channel and side channel habitats.  
One biological difference researchers might be interested in is in the number of 
invertebrate species and the abundance of those species in the main channel 
compared to the side channels.  We measured and compared system dynamics by 
determining the number of invertebrate species present and the abundance of 
invertebrates in main channel and side channel habitats.  Samples were taken 
from main channel and side channel habitats at three different locations; 
Reaches 5, 6, and 8 of the Upper Mississippi River.  Woody debris (snags) were 
randomly selected at each site.  Samples had to be at least 10 cm. below the 
surface of the water, and the part of the snag sampled could not be in contact 
with bottom sediments.  Snags were placed in the DTH snag sampler to catch any 
invertebrates that may fall off in the cutting process.  Samples were cut to 
size, put in a sample bag, and preserved with 70% ethanol.  Physical and 
chemical characteristics, including pH, temperature, current velocity, DO, 
turbidity, salinity, and conductivity were measured for each sample.  Snags were 
then cleaned in the laboratory to remove invertebrates and measured for surface 
area.  Invertebrates were sorted and identified to the lowest taxonomic level.  
Total number of taxa and total number of individuals did not differ 
significantly between habitats.  It was hypothesized that differences in current 
velocity and suspended sediment concentrations would result in greater abundance 
and diversity in side channels.  It appears, however, the nearshore zones of the 
main channel and side channels are structurally similar, leading to similar 
invertebrate communities and probably similar functional dynamics.
 
Keywords: invertebrate, community structure, diversity, main channel, side 
channel, snags