Influence of abiotic factors and macrophyte cover on zooplankton distribution in the Ketar River backwaters

Abstract

The aim of this study was to assess the relative influence of abiotic parameters and macrophyte cover on the diversity and distribution of zooplankton along the backwaters of the Ketar River. Six sampling sites were selected along the river stretch and samples were collected from December 2017 to November 2018. Zooplankton samples were collected from stagnant backpools using 30 μm mesh size plankton net. A total of 36 species of zooplankton were identified. Rotifera was represented by 28 species while Copepoda had only 2 species. Significant difference in zooplankton taxa were observed between seasons and among the study sites. Downstream site 6 was the richest both in abundance and diversity, and the species richness was significantly higher in the dry season. Mesocyclops aequatorialis was a dominant species in all the study sites. Electrical conductivity and total phosphate were the main abiotic factors that positively influenced the distribution of zooplankton in the river (Redundancy analysis). Contrary to previous finding, significantly more diverse and abundant zooplankton communities were recorded in the sites with no macrophyte cover in the Ketar River. The study indicated that both spatial and temporal changes in abiotic factors were more important than macrophyte cover for zooplankton dynamics in this important influent river into Lake Ziway.