Seasonal variations in phytoplanktonic community structure at the northern side of Lake Manzala, Egypt

Exposure of Egyptian lakes to pollution and human activities has influenced phytoplankton diversity. This study aimed to monitor physicochemical parameters of water at six sites representing the northern side of Lake Manzala, seasonal phytoplankton number and biomass in relation to environmental parameters during 2022. In addition to studying phytoplankton diversity at different sites. Analysis of water revealed that most sites maintain a slightly alkaline pH. El-Deiba recorded the highest salinity in all seasons. Towall Ibrahim have the highest total nitrogen (7.2 ± 0.18 mg/L) and total phosphorus (1.50 ± 0.02 mg/L) concentrations, whereas El-Deiba reported the lowest levels. The highest Trophic Status Index (94.5) was recorded in summer at Towall Ibrahim, whereas its lowest value (64.08) was recorded in winter at El-Deiba. The results reported 32 phytoplankton species belonging to Bacillariophytes (17 species), Cyanophytes (10), Dinophytes (4), and only one species of Xanthophytes. Cyanophytes appeared to be the dominant group in terms of cell numbers and biomass during the study period. Phytoplankton numbers and biomass decreased to the lowest level in summer. A total of 7, 21, 4, and 12 phytoplankton species were recorded in summer, autumn, winter, and spring, respectively in northern side of Lake Manzala. The diversity index and the species richness peak during autumn. Species richness had a significant positive correlation ( p < 0.05) with temperature and DO, as well as a significant negative correlation ( p < 0.05) with pH, nutrients. These results confirm the importance of increasing efforts to restore the environmental health status of the lake.