SECONDARY PRODUCTION OF TWO DOMINANT MACROINVERTBRATES INHABITING MAIN-
CHANNEL BORDER AND BACKWATER HABITATS IN THE UPPER MISSISSIPPI RIVER

Roger Haro1, Reid Northwick 1,2, and William Richardson2

1River Studies Center, University of Wisconsin-La Crosse, La Crosse, 
Wisconsin 54601, USA
2U.S. Geological Survey, Upper Midwest Environmental Sciences Center, La 
Crosse, Wisconsin 54602, USA

Large rivers, such as the upper Mississippi River (UMR), are among the most 
productive freshwater ecosystems. Macroinvertebrate production is a primary 
energy pathway to riverine fish. Much of our existing understanding of 
macroinvertebrate standing crops in the UMR has been derived from sampling 
soft sediments; however, many macroinvertebrates are unable to colonize these 
highly disturbed habitats in the main channel of the UMR. Current channel 
alignment structures and other natural hard substrates (e.g., tree roots, 
logs and branches) may provide stable, alternative habitats that support 
greater levels of macroinvertebrate production. We investigated the 
colonization and secondary production rates for macroinvertebrates on stable 
substrates in the UMR. In addition, we sampled macroinvertebrates from 4 
adjacent backwater lakes (Lawrence Lake, Round Lake, Target Lake, and an 
impounded, open-water habitat near Stoddard, WI) to compare the level of 
secondary productivity between the high-flow main-channel habitats and low-
flow contiguous backwater habitats. The backwater habitats varied in their 
connectivity to the main channel of the UMR. In the spring and summer 2006, 
Hester-Dendy artificial substrates (HDAS), consisting of 14 Masonite® discs 
with a total area of 0.16 m2, were placed at 3 locations (UMR River Miles 
691.6, 693.3, and 699.8) along alignment structures. We also sampled 
backwater invertebrates from a standard area of 0.06 m2 with a Gillespie-
Brown (G-B) sampler. Three HDAS and 2 G-B samples were collected from each 
location approximately once every 4 weeks. Using image analysis software, 
video microscopy and empirical area-to-weight relationships, over 17,000 
individual macroivertebrates were identified and measured for size. Water 
temperature, an important factor affecting macroinvertebrate growth and 
production, varied during the study period and between habitat types, but not 
among sites within habitats. Filter-feeding caddisflies Hydropsyche orris and 
Cheumatopsyche campyla (Hydropsychidae: Trichoptera) dominated the 
macroinvertebrate colonists on the HDAS in both number and biomass. Standing 
crop increased rapidly between June and July across all sites and peaked in 
August then declined in September. Colonization rates were greatest, 
averaging 200 to 325 individuals m-2 d-1, in June and then monotonically 
declined to 37.5 to 56.3 individuals m-2 d-1 by September. Annual production 
rates for H. orris from UMR River Mile sites 691.6, 693.3, and 699.8 were 
379.2, 350.9 and 246.6 g dry weight m-2 yr-1, respectively. The amphipod 
Hyalella azteca (Amphipoda: Talitridae) dominated the macroinvertebrate 
community in the backwater habitats in both number and biomass. Standing 
crops peaked in July across all backwater sites. Annual production rates for 
H. azteca increased with habitat connectivity and ranged between 21.1 and 
45.8 g DW m-2 yr-1.  These initial findings suggest that colonization and 
production rates for filter-feeding caddisflies on channel alignment 
structures and, potentially, natural, snag habitats, represent a much larger 
source of secondary production for main channel areas in the UMR than 
originally thought. Rates of production for H. azteca were greater in well-
connected backwater habitats. Both habitats are likely sources of food for 
main-channel fish, however, the mode and rates of delivery are likely to 
differ substantially.

Keywords:  secondary production, Upper Mississippi River, habitat 
connectivity, large river habitats