The present study was conducted to identify the molluscan species associated with the Posidonia oceanica and Zostera marina meadows in the Marmara Sea. The investigated benthic material was taken from seven stations at depths up to 7 m by utilizing a quadrate sampler (20 \(\times\) 20 cm) and was randomly collected by snorkeling and scuba diving from three stations in 2012. Faunistic examination revealed a total of 73 mollusc species pertaining to the classes of Polyplacophora, Gastropoda, and Bivalvia. Among the identified species Haliotis tuberculata Linnaeus, 1758, Obtusella macilenta (Monterosato, 1880), and Thylaeodus rugulosus (Monterosato, 1878) are new records from the region. The families Rissoidae (13 species), Mytilidae (7 species), and Veneridae (6 species) were found in the greatest number of species, and the most abundant mollusc species included Bittium reticulatum (da Costa, 1778) (63.70% of the total number of individuals), and Rissoa ventricosa Desmarest, 1814 (18.40%). According to Pearson’s correlation analysis, the number of species and the number of specimens exhibited positive correlations with phosphorus (r = 0.86 and r = 0.72, p < 0.05). CCA analysis revealed that Chl-a was correlated with the first axis, whereas salinity, Chl-a, dissolved oxygen, and phosphorus were connected with the second axis.
