Comparative ecology of crustaceans in relation to physico-chemical parameters from three rivers in southern Ethiopia

Abstract

This study documents the diversity and spatio-temporal distribution of crustaceans from three perennial rivers (Beshir, Kalte and Olbiyawa) that flow through an urban area in Wolaita Sodo town, southern Ethiopia. Field data and laboratory-based spatio-temporal scale studies were employed for both biological and physico-chemical parameters. Water samples were collected twice monthly between November 2019 and February 2020 at three locations from each river. Identification of species was completed to genus using suitable laboratory procedures and appropriate keys. In total, 32 genera of crustaceans were identified of which 14 belonged to the sub-class Copepoda, 13 to Cladocera and 5 to Ostracoda. The copepods dominated (59.37%) followed by the Cladocera (35.81%) and the Ostracoda (4.82%), whereas highest total densities were found in the Olbiyawa River (7 186.67 ± 2.64 ind. l⁻¹). The Shannon−Wiener’s diversity index (Hʹ), Margalef’s richness index (e) as well as Pielou’s evenness index (J) for the diversity and population density of crustaceans were high during months with souring temperatures in addition to low rainfall, steady chemical components and availability of prey. Results also indicated that both the diversity and density of the crustacean populations in the Beshir River were significantly lower than the Kalte and Olbiyawa Rivers. The Beshir River had lower levels of dissolved oxygen, electrical conductivity, total dissolved solids and chloride concentration, while pH and temperatures were consistent with the other two rivers. The diminutive distribution of crustaceans as well as the degrading water quality parameters in the Beshir River could be due to heavy anthropogenic stress including the dumping of town domestic and industrial effluents.