Vertical distribution of Chironomidae larvae in the karstic travertine barrage Lake Visovac (Croatia)

From April 1995 to October 1996 the benthic ommunity of the karstic Lake Visovac was studied with special reference to chironomids. By origin, Lake Visovac is a travertine barrage lake and relates to solution lakes. Samples were taken along a transect from 1 to a maximum of 24 meters. Over the entire investigated period, 29 Chironomidae species were recorded. Five subfamilies of Chironomidae were represented: Chironominae (20 species), Tanypodinae (4 species), Orthocladiinae (3 species), Diamesinae (1 species) and Prodiamesinae (1 species). The chironomid community of shallower waters is generally much richer than that of bare mud (the profundal zone). Tanytarsini were the most numerous in the littoral zone, while in sublitoral and profundal zones Chironomini were most abundant. Depth and bottom type were the important variables in defining species distribution. Chironomus gr. plumosus preferred mostly deep waters, while Paratanytarsus lauterborni and species of the genus Tanytarsus favoured shallower waters with a bottom rich in decaying plant fragments. Procladius choreus was found in relatively high abundance at all sampling depths due to its ability to feed on a wide range of food items.