Spatiotemporal distribution of phytoplankton and water quality to evaluate the productivity of Eretan Waters, Indramayu, West Java

Phytoplankton play a key role in aquatic ecosystems and serve as bioindicators of environmental change. This study assessed the spatial and seasonal variations in phytoplankton and water quality in Eretan Waters, Indramayu, West Java. The research was conducted at six stations along the Eretan Waters in October 2024 and February 2025, representing the dry and rainy seasons, respectively. Data analysis included diversity indices, trophic classification via Nygaard Diatom Index and TRIX, spatial interpolation, and Principal Component Analysis (PCA) to determine key environmental drivers. A total of 43 genera were identified, dominated by Bacillariophyceae (81%), with Chaetoceros sp. most abundant. In the dry season, peak abundance reached 439.4×10⁶ cells/m³ at station L2, correlating strongly with elevated orthophosphate, ammonia, and chlorophyll-a. In contrast, the rainy season exhibited reduced phytoplankton density (0.62×10⁶ cells/m³). Estuarine stations exhibiting higher nutrient concentrations due to anthropogenic inputs, while offshore stations had greater salinity and water clarity. PCA indicated nutrient parameters explained 72.6% of the variance in the dry season, while physical factors explained 74.8% in the rainy season. A diatom-based trophic assessment classified all sites as mesotrophic. Phytoplankton communities effectively reflect anthropogenic nutrient inputs and seasonal variability, highlighting their importance for coastal environmental monitoring and management.