Phytoplankton biodiversity for water quality assessment based on saprobic index in Oransbari – South Manokwari

The biodiversity of phytoplankton plays a role in aquatic ecosystem. The saprobic index is one of the methods used to determine water quality using the composition of phytoplankton. This study aimed to examine phytoplankton biodiversity for water quality assessment based on saprobic index in Oransbari Bay, South Manokwari Regency. The study was conducted from September to November 2024, and water samples were collected using a plankton net (20μm mesh size) from 6 (six) study sites located in Oransbari Bay. Water samples were then examined for phytoplankton diversity and saprobic index. The results showed that the composition of phytoplankton reached 13 classes that distributed over 8-12 classes during the three months observations for all study sites. The number of species found varied 54-80 between September and November; while the species diversity in study sites was 1.1 - 3.4 categorized from moderate to high diversity, which determine good water conditions. The saprobic index of the water quality in Oransbari Bay was 0,63, categorized as light ß-mesosaprobic and the trophic saprobic index was the oligosaprobic level.