On the Communities of Freshwater Gastropods on Aquatic Macrophytes in Some Water Basins of Southern Bulgaria

The research was conducted through the period 2008 - 2009 in the Upper Thracian Lowland: Maritsa River in the city of Plovdiv, flood area near the bridge at UFT; Eastern Rhodopes: Varbitsa River at around 3 km south of the town of Kardzhali; Perperek River, within the village of Perperk; a pond in the village of Chernoochene. The material was collected from total of 3427 g herbage biomass from 7 plant species. On the aquatic macrophytes we generally found approximately the same diversity of species of freshwater gastropods during the cold and during the warm seasons. During the warm period we found a total of 6 species, and during the cold - 7 species. Most species we found on C. demersum, and E. canadensis. Overall for the studied water basins and seasons, the species R. auricularia, Ph. acuta and G. albus were most numerous and prefer to live on C. demersum. We calculated a narrow ecological niche of the species in most cases, where slightly wider ecological niches were registered for R. auricularia and G. albus. Largest diversity of snail communities we found on C. demersum and E. canadensis. The value of the diversity index was very low for the other species of macrophytes. We calculated low values of Sörensen's index between most of the freshwater macrophytes in relation to communities of gastropods. High similarity between the communities we indicated for C. demersum and P. pussilus, and C. muricatum, and Lemna sp., and very high between P. pussilus, and Lemna sp. We found an aggregated distribution on the macrophytes of the following species of gastropods: R. auricularia, Ph. acuta, P. corneus, P. planorbis, G. albus and occasional one for V. piscinalis, A. lacustris, and L. stagnalis.