Periphytic algae as food source for grazing chironomids in a shallow phytoplankton-dominated lake

The diet composition and use of periphyton resources by grazing chironomids associated with common reed (Phragmites australis (Cav.) Trin. ex Steud.) were investigated bimonthly, from January to November, in a shallow hypertrophic lake. Periphytic algae were represented by three genera, cyanobacteria, diatoms and chlorophytes. Cyanobacteria showed the highest relative abundances during the study. The total biomass of periphytic algae showed seasonal variation and reached the lowest values in May and the highest in November. Chironomid assemblage showed very low diversity and constituted mostly of Cricotopus sp. (gr. sylvestris), Endochironomus albipennis, Glyptotendipes sp. Depending the month of the year, larvae of these three taxa amounted 95-98% of total chironomid density. The density of chironomid larvae collected was affected by the season. The larvae fed mostly on diatoms and generally preferred the most abundant algal taxa as a food source. Diet composition of chironomid larvae showed seasonal variability and was specific for chironomid taxon and size class of larvae. The highest (44%) taxonomic (or structural) similarity between periphyton and gut contents was observed in class I larvae of E. albipennis in January.