LONGITUDINAL PATTERNS ON INVERTEBRATE PRODUCTION (DREISSENA
POLYMORPHA) IN THE UPPER MISSISSIPPI RIVER.  

Sarah E. Curl, Myra L. Kunas, and Michael D. Delong.   Large
River Studies Center and Biology Department, Winona State
University, Winona, MN 55987.  

Navigational dams have created dramatic changes in the flow
patterns of the upper Mississippi River.  Within each reach of
the river, there are now three separate hydrological patterns:
high velocity (just below a dam), normal velocity (middle of
reach), and low velocity (just before dam).  The purpose of this
study was to assess the effect of location in a navigation reach
on secondary production of a benthic invertebrate.  Four rock
samples were hand-collected from below dam, middle reach, and
above dam locations in reaches 5 and 6.  Samples were bagged and
preserved in 70% ethanol for later processing.  Zebra mussels
were removed from rocks and separated into 2-mm size classes. 
Rocks were measured for determination of surface area.  Secondary
production was estimated using the instantaneous growth method. 
Size-class specific growth rates were determined using growth
rates of mussels attached to clay tiles (refer to poster by Doyle
et al.).  New cohorts began to appear in late July and continued
to be evident through the completion of the study in late
October.  Differences were evident in secondary production, with
production highest in the middle areas of the reaches.  

Keywords:  navigation, secondary production, Mississippi River,
zebra mussel, Dreissena polymorpha