Species composition, abundance and monthly distribution of the Mollusca fauna and the physicochemical variables of Saricay Creek and Atikhisar Reservoir have been investigated between September 2005-August 2006. Mollusca fauna in Saricay Creek and Atikhisar Reservoir was represented by 21 species of Gastropoda and 8 species of Bivalvia. Diversity, dominance and frequency were recorded monthly. By assessing the data via Shannon-Wiener index, Saricay Creek had an index of 2.58 richness at 8th station while, third station in Atikhisar Reservoir had the poorest with an index of 0.02. According to Bray-Curtis similarity index, the first and third stations were found to be very similar to each other, while 8th and 66 h stations were observed to be the most different from all of the other stations in terms of the dynamics of mollusca fauna. Dreissena polmorpha were the most dominant of 47.16% and frequent species of 48.96%, especially encountered in the Atikhisar Reservoir. The results of One-way Analysis of Similarity (ANOSIM) showed that mollusca compositions were significantly different between sampling sites (p<0.05). ANOSIM and Similarity Percentage analysis (SIMPER) revealed significant differences and a high degree of community dissimilarity within and between the sampling stations. The relationship between the dynamics of organisms and environmental parameters were analyzed using Canonical Correspondence Analysis. This study pointed out that water quality parameters especially COD, BOD, Anionic Detergent, salinity, TP, TN, temperature were effective on the abundance and distribution of Mollusca fauna.
