Influence of Fish Predation on Assemblage Structure of Macroinvertebrates in an Intermittent Stream

Ahstrucf.-Despite considerable investigation of stream systems, the influence of fish predation on macroinvertebrate assemblages is still poorly understood and remains a controversial subject. We conducted a field experiment in an intermittent reach of Alum Creek in the Ouachita Mountains, Arkansas, to examine the effects of predatory fish on macroinvertebrate assemblages. We tested the prediction that with pool isolation fish would have a top-down influence on macroinvertebrate assemblages. Overall, fish had a significant effect on both the density and assemblage structure of the macroinvertebrates in isolated stream pools. Assemblage effects may be linked to a feeding preference for relatively rare food items. These patterns were evident despite the loss of replicates (i.e., the drying of individual pools), indicating a strong short-term predator effect. We suggest that the use of different methodologies among studies makes it difficult to determine the influence of fish predation on macroinvertebrate assemblages in stream systems. Furthermore, we suggest that more realistic field experiments (i.e., with natural stream setting, hydrology, and substrata) must be conducted to fully understand and adequately address the question of the effects of fish predation on macroinvertebrates