Colonisation trends, community and trophic structure of chironomid larvae (Chironomidae: Diptera) in a temporal phytophylous assemblage

Abstract

Spatial and temporal trends of a phytophylous chironomid community on the submerged plant species Ceratophyllum demersum L. were investigated in a eutrophic lake (Lake Sakadas, Danube floodplain area in Croatia) during summer 2004. The study also included an analysis of functional feeding groups (FFG) and the influence of environmental parameters on the chironomid community. Within macrophyte stands at three sites, the chironomids were very abundant and the recorded larvae belonged to three subfamilies: Chironominae (Chironomini and Tanytarsini), Orthocladiinae and Tanypodinae. Endochironomus albipennis type was the dominant species with high abundance in July and September and lower abundance in August, most likely due to summer emergence. At the beginning of the sampling season, high abundance was recorded for Cricotopus sylvestris type as well. The secondary colonizers, Polypedilum sordens type, Glyptotendipens pallens type and Parachironomus varus type, displayed an increase in abundance towards the end of the season. ANOSIM analysis indicated significant differences in chironomid abundance between samples from July and September as a result of the higher abundance of Chironomini larvae in September. Active filterers, detritovores and predators were more abundant in September as compared to the other two months, while grazer abundance decreased towards the end of the study period. ANOSIM analysis separated August and September based on the abundance of different functional feeding groups (FFG). We found no significant differences between research stations for either chironomid abundance or FFG. BIO-ENV analysis indicated an influence of environmental variables, especially water temperature, Secchi depth and oxygen concentration on chironomid abundance.