Water quality parameters influence temporal dynamics of zooplankton community structure in a tropical highland lake, Lake Tana, Ethiopia

Assessing long-term trends in zooplankton community structure is essential for the monitoring of aquatic systems. However, there is paucity of information on zooplankton community structure in Lake Tana's northern gulf. Therefore, this study aimed to provide baseline information on the spatio-temporal variations in zooplankton assemblages in Lake Tana's northern gulf, focusing on water quality parameters. Data were collected from five sampling sites from May 2023 to April 2024. Forty-five zooplankton species belonging to three groups (17 Rotifera, 14 Copepoda, and 13 Cladocerans) were identified. Rotifers were the most species-rich group, with Brachionus angularis, B. caudatus, B. falcatus, B. havanaensis, and Keratella tropica being the most abundant. Significant (p < 0.05) spatial variations in zooplankton diversity, evenness, and dominance were recorded. Shannon index values ranged from H^'=2.98 for the GOR site to H^'=3.49 for the MEG site. Evenness values varied between 0.52 and 0.74, indicating less uniform distribution. Zooplankton taxa were rare at the water hyacinth-infested site probably due to stress from low light and reduced temperature. Copepods and rotifers showed resilience to survive in the slightly polluted water of the littoral region, while cladocerans preferred the clear pelagic water. Zooplankton community structure showed a similar pattern across all sites, with minimum (27) and maximum (36) species richness occuring during the rainy and post rainy seasons, respectively. Generally, the spatio-temporal variations in water quality parameters had implications for zooplankton community structure.