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.