Primary inventory of phytoplankton as ecological bioindicators in the Lobe Estuary, Kribi (Southern Cameroon).

Estuaries are key reservoirs of coastal biodiversity, yet increasingly exposed to climatic variability and anthropogenic pressures highlighting the need for reliable ecological indicators to support their management. This study assessed the ecological health of the Lobe Estuary (southern Cameroon) through an integrated analysis of phytoplankton communities and physicochemical parameters. Sampling was conducted at three stations along the upstream-downstream gradient during the short dry season (July 2022) and the onset of the main rainy season (September 2022), using standard physicochemical and phytoplankton sampling protocols. Physicochemical conditions showed moderate spatial variability, with chlorophyll a averaging 11.13 ± 5.3 µg L-1 and a relatively stable temperature (24.46 ± 1.72 °C), consistent with generally acceptable water quality. A total of 74 phytoplankton species across 10 classes were identified, dominated by Chlorophyceae (20.6%) and Bacillariophyceae (19.5%), a pattern commonly reported in tropical estuarine systems. Shannon-Wiener and Simpson indices indicated relatively high species diversity and an overall moderate ecological status during the study period. The occurrence of potentially harmful taxa (Lyngbya sp. and Nostoc sp.), together with a maximum chlorophyll a concentration of 27 µg L-1, indicates a potential risk of localized algal proliferation. Principal component analysis revealed clear associations between phytoplankton assemblages and environmental gradients, suggesting that community structure was influenced by multiple environmental factors. These findings provide baseline evidence for phytoplankton as a bioindicator of ecological status in the Lobe Estuary and support regular, multiseasonal monitoring, particularly at the estuary mouth, to track bloom risk and inform the management of agro-industrial pollutant inputs.