Abundance, Species Composition and Spatial Distribution of Planktonic Rotifers and Crustaceans in Lake Ziway (Rift Valley, Ethiopia)

Abstract

Species composition, abundance, and spatial distribution of rotifer and crustacean zooplankton were studied in Lake Ziway from late April to early July 2004. A total of 49 rotifer species was recorded, with Anuraeopsis fissa, Brachionus angularis, Filinia novaezealandiae, and Trichocerca ruttneri being numerically dominant. Variation in abundance was extremely high, ranging from 2 to 1000+ individuals per litre. There was no significant difference in the distribution of rotifer species between inshore and offshore regions. Crustacean species richness was low, with only five cladoceran and three copepod species occurring in the open water. Moina micrura and Diaphanosoma excisum dominated the cladoceran community, whereas Thermocyclops decipiens was the dominant copepod. Although numerically dominant (75%), rotifers accounted for less than 30% of mean total zooplankton biomass. Peak abundance of crustaceans was observed in May and June, following the onset of the rainy season and increased phytoplankton production. Variation in the spatial distribution of crustacean species was neither observed horizontally between inshore and offshore areas nor vertically in the highly turbid and wind exposed deeper part of the lake. On the other hand, Moina micrura varied significantly in size between inshore and offshore areas. Adult M. micrura dominated offshore, whereas juveniles were more abundant inshore, suggesting a predominantly littoral selective predation on large and adult crustaceans by fish.

Zooplankton abundance, species composition and ecology of tropical high-mountain crater lake Wonchi, Ethiopia

“…The pelagic zooplankton standing biomass in Lake Wonchi showed seasonal variation and positive correlation with Chl-a concentrations, which mirrors a bottom-up effect of phytoplankton on zooplankton dynamics in the lake, which has also been documented elsewhere (Brooks and Dodson, 1965;Jeppesen et al, 1997). The decline in zooplankton biomass during the rainy season was likely caused by low abundance of total copepodites during this period (abundance: dry season 118x10 3 Ind m (Wondie and Mengistu, 2006;Dagne et al, 2008;Fetahi et al, 2011;Haileselasie et al, 2012). The zooplankton abundance of Lake Wonchi was dominated by Thermocyclops ethiopiensis (50%) and cladocerans (38%), which is in agreement with several other authors, who also reported low abundance of rotifers compared to crustacean in other highmountain tropical lakes (Gillooly and Dodson, 2000;Fetahi et al, 2011;Dejenie et al, 2012;Haileselasie et al, 2012).…”

“…For instance, a seasonal study on zooplankton community composition from the high altitude tropical Lake Hayq showed that Thermocyclops ethiopiensis and D. magna were very abundant (Fetahi et al, 2011), which is in accordance with this study. The high abundance of crustaceans is quite exceptional to the scenario observed in most lowland tropical water bodies, where the less competitive and smaller planktonic species, mostly rotifers, predominate (Nilssen, 1984;Fernando et al, 1990;Dumont, 1994;Dagne et al, 2008). The possible explanations for the paucity of rotifers in Lake Wonchi could be either high predation from the abundant Thermocyclops ethiopiensis or the possible interference and exploitative competition from D. longispina for limited food sources (mean algal biomass Chl-a: 3.1±1.6 µg L -1 ).…”

“…Former studies were based mainly on samples collected by expeditions, and thus provided scanty information on long-term patterns in their seasonality and dynamics. Nevertheless, our understanding on zooplankton in East Africa has been slowly developing (Defaye, 1988;Fernando et al, 1990;Mengestou et al, 1991;Dagne et al, 2008). Some studies were able to explore zooplankton associations along ecosystem gradients mainly in the rift valley region and the Bishoftu crater lakes (Wodajo and Belay, 1984;Green and Mengestou, 1991;Mengestou and Fernando, 1991;Vijverberg et al, 2014).…”

Biochemical nutrient requirements of the rotifer Brachionus calyciflorus: co‐limitation by sterols and amino acids

“…Rotifers are important components of freshwater food webs (Walz ) that can dominate the zooplankton with densities often >1000 individuals per litre (Modenutti ; Dagne et al . ). By feeding on bacteria, algae, heterotrophic nanoflagellates and ciliates (Pourriot ; Sanders et al .…”

Structure of rotifer assemblages in shallow waterbodies of semi-arid northwest Iran differing in salinity and vegetation cover

“…They have also been investigated across different geographical regions including tropical (Dagne et al, 2008), subtropical (Havens et al, 2007), and temperate (Kuczyńska-Kippen, 2005) areas globally.…”