Zooplankton Composiiion and Seasonal Dynamics in Lake Ziway. Ethiopia
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Date
1988-06
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Addis Ababa University
Abstract
The species compositilln and seasonal dynamics (abundance) of zooplankton
in Lake Ziway (a tropical lake) was studied from f1arch 19,H to f1arc, h 19UB.
Bimonthly vertical haul zooplankton samples were taken from 3 stations (2
stations in the limnetic zone and 1 in the littoral zone) using a 61[)Jill
mesh net. The 1 imnet ic community was domi nated by eycl opoi d cupepods \'Ihil e
the 1 ittoral community by the Hotifera. Ca 1 anoi d copepods and
ffarpacticoids did not appear in the samples collected. The Cyclopoid copepod species identified and counted in each sample
included f1icrocyclops vilricans and Nesocyclops ~equatorialis. 6frocyclops
species was found in only three of the sampling periods. Diaphanosoma
excisum and Alona davidi constituted the cladoceran population of the lake.
The Rot ifera were domi nant in terms of thf? number of speci es. Out of the
13 species of Rotifera identified, the numerically dominant species was
Brachionus angularis and the least ilbundant species were ~. falcatus and
Lecana luna which were encountered in (lnly two and one sampling periods
respect i ve ly. r~i nor groups of zooplankton recorded inc 1 uded Chi ronomi d
larvae, the Ostracod Cypria javana, an unidentified nematod and an
unidentified i1rthropod larva. 1111 major zooplankton groups and species identified shol'lcd significant
seasonal variation in their abundance. Copepods and cladocerans both at
group and spec i es 1 eve 1 s hO~led max i mum abundance du ri n9 the I'let sea son and minimum abundance during t.he dry season. The Roti fera in general peaked
after the rainy season. t,1aximum contribution to the annual total
zoop 1 ankon abundance came from eyc 1 opoi d zoop 1 ankters. The abundance
pattern of the zooplankton of the lake are discussed in relation to
suggested environmental factors.