HABITAT RELATED DIFFERENCES IN SECONDARY PRODUCTION OF HYDROPSYCHID CADDISFLY 
LARVAE IN THE UPPER MISSISSIPPI RIVER

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

Rivers are heterogeneous systems in which structural and functional differences 
affect secondary production.   An example of this habitat heterogeneity is 
evident in comparing main and side channel habitats.  Both systems are lotic 
habitats in large river ecosystems, however, several factors, including current 
velocity, depth, and nutrient dynamics, may cause the two habitats to function 
differently.  One approach to assessing ecosystem function is to measure 
secondary production.  Bioenergetics deals with the capture and fate (or flow) 
of energy in biological systems, whether dealing at organism, population, or 
ecosystem level.   The objective of this study is to assess spatial and temporal 
changes in secondary production of hydropsychid caddisfly larvae in main and 
side channel habitats of the upper Mississippi River.  The two prominent larvae 
studied were Hydropsyche and Cheumatopsyche, but production was estimated only 
for H. orris.  Samples were taken from three sites on the Upper Mississippi 
River at Reaches 5, 6, and 8.  Woody debris (snags) were collected from main 
channel and side channel habitats of the river.  Snags collected were at least 
10 cm below surface and not completely on the bottom sediments.  Snags were 
placed in a DTH sampler to catch any lose invertebrates, cut to size, bagged, 
and preserved with 70% ethanol for later analysis.  Physical and chemical 
characteristics, including pH, temperature, current velocity, dissolved oxygen, 
turbidity, and conductivity were measured for each sample.  Snags were cleaned 
in the laboratory to remove invertebrates, and were then sorted and later 
counted and identified to the lowest possible taxonomic level.  Secondary 
production of H. orris was estimated using the increment-summation method.  
Because secondary production is an indicator of energy flow, production by H. 
orris should reflect differences in food quality and availability in these lotic 
habitats.  We found no significant differences in densities or rates of 
secondary production.  It would appear, therefore, that main channel and side 
channels, while appearing to differ structurally at a macrohabitat scale, 
function similarly at least for nearshore mesohabitats.

Keywords: invertebrate, Hydropsychidae, caddisfly, secondary production, main 
channel, side channel, snags