Abstract
Daphnia are important components of zooplankton communities in lakes, ponds and reservoirs. Currently freshwater ecosystems are affected worldwide by Cyanobacterial blooms through the process of eutrophication. The objective of this study was to provide experimental evidence to the response of Daphnia to various concentrations of Microcystis . The experiment contained four treatments and two controls each with three replicates. The first control contained D . cf. similis without Microcystis and the second control contained Microcystis without D .cf. similis . The remaining four treatments contained both D . cf. similis and Microcystis at different concentration of Microcystis .. The results showed a significant negative relationships between D . cf. Similis and Microcystis across the treatments (F=294.5; p<0.00). From the four Microcystis concentration gradients, we found mortality of D. cf. Similis in HMC (high Microcystis concentration) and 67% of the original HMC gradient while in the other treatments, in 43% and 22% original HMC treatment, D . cf. Similis reproduce and attain high density. Therefore, from these results it is concluded that D . cf. similis can control the growth of Microcystis if the concentration is low but they cannot reduce an already existing bloom. Keywords : Concentration gradient, D. cf. Similis, Feeding-treatment, Microcystis, Ethiopia.
Highlights
Understanding, managing and learning about freshwater ecosystems has become increasingly significant throughout the world as the development of land continues to expand and as knowledge of the impact increases
D. cf. similis were isolated from the sample and were transferred individually into plastic jars using a pipette with a large tip opening
There are other supporting evidences that indicate ingestion of Microcystis by Daphnia species (Rohlack et al, 2001). This indicates that D. cf. similis was able to feed on Microcystis and result in decrease in the density of Microcystis in lower and medium treatments
Summary
Understanding, managing and learning about freshwater ecosystems has become increasingly significant throughout the world as the development of land continues to expand and as knowledge of the impact increases. Due to the frequency of algal blooms in the world, as a result of intense, hot summers, there has been an increasing awareness of the associated issues including the creation of anoxic conditions, and risk of intoxication for those exposed to toxic cyanobacteria (Codded et al, 2005). Freshwaters such as lakes, rivers and reservoirs are the most important resources, especially in the tropics, where they are often viewed as highly productive biological systems.
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