Abstract
The study aim was to determine changes in molluscan communities under chemical and thermal stress in the River Nile at Assiut, Egypt and to analyse the relationships between molluscan communities and environmental variables. Molluscan communities were studied in the River Nile at four sites: Site I as a control, Site II as a thermally polluted site, and Sites III and IV as chemically polluted sites. Monthly samples were collected over one year from June 2010 until May 2011. Water temperature, pH, salinity, turbidity, dissolved oxygen and water current were measured at the time of sampling. Significant differences were detected between investigated sites and seasons in the environmental variables as well as in species density, richness and Shannon diversity. Species numbers ranged between 10 (in July at Site I) and 41 (in February at Site IV) species in the collected samples. Stepwise multiple regression showed that molluscan density and diversity were most affected by water temperature and salinity, whereas Bivalvia were affected by pH and water current.