ABSTRACT This research was carried out in March 2022, the location of this research is Pandaratan Beach, Central Tapanuli Regency, North Sumatra Province. The purpose of this study was to determine the abundance, relative abundance, diversity index, dominance index and uniformity index of epizoic diatom species in Pinna muricata in the seagrass ecosystem of Pandaratan Beach. The method used is…