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

Abstract

Spatial and seasonal patterns in the densities and species richness of Simuliidae (blackflies) were examined in the glacier-fed Roseg River, Switzerland. We also investigated how selected environmental factors were related to the observed community structure. Overall, 7 blackfly species were found in streams of this glacial flood plain. Total densities and species richness differed significantly among sampling dates, and densities showed a significant downstream increase. Non-metric multidimensional scaling supported these 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 high discharge conditions in summer. This resulted in enhanced overall ecosystem stability in this glacier-fed stream ecosystem, and enabled biotic assemblages to sustain populations under the harsh environmental conditions experienced at this time of the year. Low temperatures and channel instability limited Simuliidae colonization close to the glacier terminus. Suspended particles represented the most important food source for simuliids in the Roseg River.