Diversity, distribution and seasonality of the Simuliidae fauna in a glacial stream system in the Swiss Alps

Spatial and seasonal patterns in the densities and species richness of Simu liidae (blackflies) were examined in the glacier-fed Roseg River, Switzerla nd. We also investigated how selected environmental factors were related to the observed community structure. Overall, 7 blackfly species were found i n streams of this glacial flood plain. Total densities and species richness differed significantly among sampling dates, and densities showed a signif icant downstream increase. Non-metric multidimensional scaling supported th ese findings and suggested that seasonal changes were affected strongly by extent of glacial influence. Furthermore, our results were indicative that spatio-temporal habitat heterogeneity ameliorated the negative effects of h igh discharge conditions in summer. This resulted in enhanced overall ecosy stem stability in this glacier-fed stream ecosystem, and enabled biotic ass emblages to sustain populations under the harsh environmental conditions ex perienced at this time of the year. Low temperatures and channel instabilit y limited Simuliidae colonization close to the glacier terminus. Suspended particles represented the most important food source for simuliids in the R oseg River.