Seasonal variation in the Chironomidae (Diptera) communities of two Faroese streams

Seasonal variation of freshwater invertebrate communities is strongly influenced by abiotic factors including temperature and precipitation which, in turn, are predicted to be affected by climate change. It is important to study these effects, not least since they may affect higher trophic levels and ecosystem dynamics. Our aim with this study was to compare the seasonal variation of the community composition of Chironomidae (Diptera) in two streams in the Faroe Islands and to see how this related to abiotic factors. Additionally, we studied the life cycle of Tvetenia calvescens (Edwards 1929), the dominant species in the streams. For this purpose, Chironomidae larvae were collected from two adjacent streams of different sizes in the Faroe Islands at regular intervals over the course of 15 months. We found that Tvetenia calvescens was the most abundant species in the streams, followed by Eukiefferiella minor (Edwards 1929). The community composition varied in different months and between the two streams and was shaped by water temperature and flow velocity. Larval densities were generally higher in the smaller stream than in the larger stream, but densities were not correlated with water temperature, monthly temperature amplitude or flow velocity. We found that in both streams Tvetenia calvescens was bivoltine with adult emergence in May/June and September/October.