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Title: ZOOPLANKTON COMMUNITY GRAZING IN LAKE KURIFTU
Authors: GIRUM, TAMIRE
Date Added: 31-Aug-2007
Abstract: Studies on zooplankton community grazing rates were done in Lake Kuriftu from July 2005 to April 2006 using food removal method with chlorophyll ‘a’ as algal food indicator. The study considered the main factors that affect zooplankton community grazing rates such as density and size of both grazers and phytoplankton. Mean grazing rate at the natural density of zooplankton was 59.3% per day during the study period. Grazing rate values ranged from 18.3 % to 135.6% per day at both sites and all months. Increasing zooplankton density at two to four times ambient density was found to decrease grazing rates. Grazing rates were higher for larger zooplankton (>250mm) than smaller ones (<250mm). Pico and nanoplankton (up to 20mm) especially those of size <10mm were found to be more easily removed than microplankton (up to 63mm). Increasing the natural food density decreased grazing rates while diluting the algal food concentration increased rates, even at ¼ dilution factor. The Cyclopoid Thermocyclops consimilis dominated the zooplankton community during the study time followed by the rotifer Brachionus sp. The results suggested that increasing the density of zooplankton in Lake Kuriftu will reduce grazing rates; and on the other hand the natural food concentration should be diluted to increase zooplankton impacts through grazing. Top-down control with large-sized zooplankton can bring the reduction of chlorophyll ‘a’ concentration in the lake only on smaller and non-cyanobacterial phytoplankton (<10μm). The control of larger phytoplankton and nuisance cyanobacteria may be of limited use using the existing zooplankton community. Controlling external nutrient inputs into the lake should be given priority in controlling the algal productivity of the lake, since bottom-up route is significantly important in controlling larger and filamentous cyanobacteria. However top-down approaches should not be ignored since large-sized zooplankton grazers have contribution in removing smaller-sized phytoplankton.
Description: A Thesis Presented to the School of Graduate Studies of the Addis Ababa University in Partial Fulfillment of the requirement for the Degree of Master of Science in Biology
URI: http://hdl.handle.net/123456789/42
Appears in:Thesis - Biology

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