Mollusc species diversity in 0.5 m depths of the hard substrate type coasts of Gokceada was investigated qualitatively and quantitatively, seasonally and monthly in 2010 and 2011. In addition, the mucilage event, which occurred in the Marmara Sea in 2020 and which also affected Gokceada due to the currents, was sampled in the summer of 2021 to investigate the mollusc fauna. A total of 77 mollusk species were identified and 27 of these species are new records for Gokceada. While Cardita calyculata (Linnaeus, 1758) is the most dominant species at the Yıldız Koy station which is sampled monthly, the most dominant species is Musculus costulatus (Risso, 1826) at all other sampling stations. The TP station was found the highest number of species and individuals. Limited human access to this area, different habitat types and also a small freshwater inflow can be shown as the reason for this situation. The low mollusc species diversity, which was detected in 2010 due to the pouring of sand for tourists by the municipality at Yıldızkoy station, has been revealed to have increased greatly in 2021 after this practice was abandoned. These results suggest that mollusc species living on the coasts of Gokceada are not acutely affected by mucilage. However, more detailed studies are needed to monitor and report this region in order to detect the negative effects that may occur in the region today and in the coming years and to protect the species diversity in this region.