TEST  FOR  COMPETITIVE  INTERACTIONS  BETWEEN  ZEBRA  MUSSELS   AND
HYDROPSYCHID CADDISFLIES

Jessica Konz, Kristin Mack, and Michael Delong.
Large River Studies Center, Biology Department, Winona State University, Winona, 
MN 55987.
  
Numerous studies have documented the abiotic and biotic effects of zebra mussels in 
the Great Lakes.  In contrast, only a limited amount of research has been published 
documenting the same effects in river ecosystems.  Students working in the Large 
River Studies Center since 1993 have observed that the abundance of some 
invertebrate fauna is negatively affected by increasing zebra mussel densities.  Of 
particular note is a possible negative effect on hydropsychid caddisflies, an abundant 
and potentially important aquatic insect larvae in terms of biomass generated and 
potential as a food source for fish.  This study was designed to test observations that 
zebra mussels may negatively affect hydropsychid caddisflies experimentally.  Zebra 
mussels were attached to unglazed clay tiles using aquarium sealant at three 
densities: no mussels, low densities (=500 mussels/mư), and high densities (=1,500 
mussels/mư).  Four replicates were placed at each of four sample sites in Reach 6 of 
the upper Mississippi River.  One tile for each treatment (n=4) was removed from 
each site monthly.  Tiles were returned to the lab, examined for newly colonized 
mussels and cleaned to remove caddisflies.  Hydropsychid caddisflies were identified 
and counted.  Preliminary analysis of samples suggest there was no relationship 
between zebra mussel and hydropsychid densities.  Results of this study, however, 
may be inconclusive because of the loss of mussels attached to tiles.

Keywords:  zebra mussel, competition, biotic effects, experiment, Mississippi River
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