INFLUENCE OF NONPOINT SOURCE SEDIMENTATION ON GLOSSOSOMA
SPP (TRICHOPTERA: GLOSSOSOMATIDAE) FORAGING BEHAVIOR IN
SOUTHWESTERN WISCONSIN STREAMS

Deric R. Deuschle, Kenneth J. McElroy and Roger J. Haro
River Studies Center, Department of Biology & Microbiology, University of
Wisconsin - La Crosse, La Crosse, WI 54601

Nonpoint source pollution in streams, including deposited sediment, is a
ubiquitous water quality problem.  Degradation of benthic habitats by
sedimentation is well documented.  Previous studies have primarily focused on
physical effects of sedimentation on the density and community structure of
organisms in aquatic habitats.  Behavior of benthic organisms under differing
levels of sedimentation is poorly understood.  Examination of behavioral responses
of these organisms may reveal mechanisms by which benthic structure in stream
communities is ultimately altered by sedimentation.  The larval caddisfly
Glossosoma is a common herbivorous insect found in the headwaters of many
spring-fed streams.  Because of their high densities and grazing efficiency, they
play an integral role in shaping the composition of the benthic community. 
Changes in Glossosoma populations affect local food web dynamics.  A negative
correlation between Glossosoma densities and periphyton standing crop has been
observed.  As grazers, Glossosoma larvae are dependent upon periphyton resources
on hard, stable substrates.  In conjunction with foraging theory, it is our hypothesis
that the larvae will demonstrate measurable changes in feeding behavior and
movement as levels of sedimentation alter the availability of these types of
substrates.  Biological samples and physical habitat information was collected
monthly from March 1997 to November 1997 from seven streams with different
levels of deposited sediment.  The mean density of larvae among sites ranged
between 244 and 5400 individuals per m-2.  The degree of substrate embededness
among the sites ranged between 0 and 50%.  Preliminary analyses suggest a
correlation between densities and embededness.  Using information gained from
our field study, a detailed analysis of larvae behavior will be conducted in the
laboratory.  Time-lapse video techniques will be used to record and measure
Glossosoma responses to substrate manipulations in artificial streams. 
Experiments will mimic natural sedimentation impacts, including reductions in
surface area, and increased fragmentation and isolation of large substrate particles.

Keywords: nonpoint source sedimentation, invertebrate, foraging theory, behavior,
artificial stream


Deric Deuschle
University of Wisconsin-La Crosse, Biology Department, La Crosse, WI 54601
Phone: (608) 785-6997     FAX: (608) 785-6959
e-mail: deusc_dr@students.uwlax.edu
Poster presentation only
Student author