Biomass and production of the major dominant crustacean zooplankton in a tropical Rift Valley lake, Awasa, Ethiopia

Seasonal variation of the biomass (B), production (P) and P/Bratio of the numerically dominant crustaceans in Lake Awasa(Mesocydops aequatonalis stmilts, Thermocyclops consunilis andDiaphanosoma exisum) were studied during 1986 and 1987. Quantitativenet samples (64 (xm mesh) were taken at three stations on 10day intervals throughout 1986, and the dry weights and developmenttimes for each life stage were obtained from laboratory measurementsand cultures Total biomass of most of the dominant crustaceans,determined from 390 samples during 1986, was 44.85 mg m^–3(dry weight, DW) with adult females of Mesocyclops making >43.5%.Alona diaphana, another common crustacean, is dealt with ina separate paper, as are the Rotifera. Production of the dominantcrustaceans during 1986 was estimated by the growth incrementsummation (Winberg) and instantaneous growth (Ricker) methodsThe annual integrated production of the two dominant cyclopoidsis 535.2 mg (DW) m^–3 (Winberg) while annual crustaceanproduction totals 2.5 g (DW) m^–3 (Ricker) The mean annualP/B ratio for individual species and stages varied from 221.0for Diaphanosoma, to 121.7-143.0 for nauplii and 9.8–187 for copepodites of the cyclopoids It was 55 8 for the dominantzooplankton species Low or high zooplankton production and biomassturnover rates (P/B) cannot be used to characterize all tropicallakes consistently However, production per unit biomass is likelyto be higher in tropical lakes.