Assemblage composition and ecological features of aquatic dance flies (Diptera, Empididae) in the Cetina River system, Croatia

Abstract

Twenty species of aquatic dance flies (Empididae: Clinocerinae and Hemerodromiinae) were recorded from the Cetina River system, Croatia. No previous such research has been done on any Mediterranean river con-cerning aquatic dance flies. Aduit dance flies were sampled at 7 locations with an aspirator and sweep nets between May and September 2005 and in March and April 2006. The most abundant species was Wiedemannia (Wiedeman-nia) bistigma which was present in ali months but only at locations in the lower reach of the Cetina River. Larvae were sampled at 6 sites from different microhabitat types. Altogether 241 quantitative samples were taken at 20 sampling points between August 2004 and August 2005, but dance flies vvere found only in a small number of the samples. The relationships between dance fly assemblage structure and selected environmental variables (water temperature, dissolved oxygen, alkalinity, conductivity and pH) vvere investigated and showed that the most im-portant environmental variable was water temperature. Some species clearly preferred sites where the mean annual water temperature was constant and lower year round, like springs (e.g., Chelifera spp., Wiedemannia (Philolutra) kacanskae, Wiedemannia (Chamaedipsia) ariadne), while other species preferred sites where the mean annual water temperature was higher (e.g., Hemerodromia spp., Wiedemannia (Wiedemannia) tricuspidata, Wiedeman-nia {; ; ; Pseudowiedemannia) lamelatta). Some species did not show any strong preferences for any of the selected parameters (e.g., Wiedemannia (Eucelidia) zetterstedti, Wiedemannia (Wiedemannia) bistigma, Dolichocephala guttata). A significant positive correlation emerged between the amount of prey present in different microhabitat types and the number of dance fly larvae. A significant difference was also found between microhabitat types and total number of dance fly larvae.