Zooplankton community structure in relation to environmental variables in a tropical endorheic Soda Lake Shala, Ethiopia

Abstract

Lake Shala, endorheic Soda Lake in the Ethiopian Riftvally Lake, supports an enormous biodiversity, with a large human population and economic development. However soda lakes are under several ecological changes, with unexpected shifts in biodiversity composition and physicochemical changes. This study focuses on assessing the community structure of zooplankton in Lake Shala. Samples were taken at monthly intervals from January to December 2018. A total of 32 zooplankton species were identified, of which 23 species were Rotifers and followed by Copepoda (6) and Cladocera (3). The community was dominated by Brachionus dimidiatus, B. dimidiatus inermis, B. plicatilis and B. calyciflorus. Their abundance exhibit significant seasonal and vertical variations (ANOVA, p<0.05). Zooplankton community structure of Lake Shala has changed over time, benthic harpacticoids (Nitocra lacustris) have become replaced by small-bodied and generalist-feeder rotifers (genus Brachionus). Such ecological shifts may be driven mainly by partial atelomixis in this deep tropical lake. Overall, zooplankton species distribution and abundance are influenced by various environmental factors such as conductivity, salinity, Chl-a and nutrients. This study concludes that the composition and community structure of zooplankton in Lake Shala has changed over time with the change in physicochemical and internal limnological dynamics (atelomix).