Caddisfly (Trichoptera) larvae distribution in the Maple River.

Abstract

Caddisflies of the three superfamilies, Spicipalpia, Integripalpia, and Annulipalpia, produce cases during an aquatic larval stage to aid in their growth and development. The distribution of these cases in rivers and streams is dependent on the interplay of biotic and abiotic factors. In our study we focused on several of these factors that affect caddisfly larval distribution including water depth and velocity, algae cover, and rock surface area. We also looked at case location on individual rocks (upstream versus downstream, and top versus bottom). To study these differences, we examined caddisfly distribution in three sections of the Maple River: the East Branch, the West Branch, and the Main Branch south of Lake Kathleen where the East and West branches merge. We found a significant difference in distribution among the three sites with Spicipalpia and Integripalpia preferring the West Branch and Annulipalpia preferring the East and Main branches. We found no difference in the mean water depth between rocks found with caddisfly larvae and rocks found without larvae. However, we observed a difference in the water velocity flowing over rocks with Spicipalpia and Integripalpia present, which were more common in fast waters. Annulipalpia and Integripalpia appeared more frequently on rocks with high algae cover while Spicipalpia were more common on rocks with low and medium coverage. We also observed that all three sunerfamilies were more prevalent on the tops of rocks and that both Spicipalpia and Annulipalpia were more frequently found on the upstream side. We believe that a larger sample size would help to further distinguish the differences in distribution of caddisfly larvae.