Species Content and Distribution of the Macrozoobenthos along Rilska River, South-West Bulgaria

Rilska River is one of the left tributaries of Struma River and it is a substantial source of drinking water for the capital city of Sofia. In spite of that the hydrobiological data are quite poor, especially these concerning bottom invertebrate fauna. This study presents the results from research on the macrozoobenthos species composition carried out in 2007-2008 at six sites along the river. During the study period totally 192 benthic taxa were found. The relatively high taxa richness and the presence of species sensitive to pollution at all investigated sites are indicative of stable low-saprobic conditions in the river. It was determined that the species composition along the river continuum differed significantly in the upper and lower part of the river and a tendency of increasing species richness downstream the river was observed.