PRODUCTION BIOLOGY OF COPEPODS AND CLADOCERANS IN 3 SOUTH-EAST SRI-LANKA LOW-LAND RESERVOIRS AND ITS COMPARISON TO OTHER TROPICAL FRESH-WATER BODIES

Production, biomass and productivity of the microcrustacean zooplankto n populations of three low-land reservoirs, Tissawewa (eutrophic), Rid iyagama (moderately eutrophic), and Muruthawela (mesotrophic) in South -east Sri Lanka were studied. The temporal variation of zooplankton pr oduction was studied in Tissawewa on basis of fortnightly sampling on five fixed sampling stations for 2 years. Zooplankton production was r elatively high, mainly because of high copepod production predominantl y realised due to two calanoid copepods, Phyllodiaptomus annae and Hel iodiaptomus viduus. About half of the copepod production was contribut ed by the naupliar instar stages, whereas the contribution of the eggs was generally much smaller (<20%). In contrast, the cladoceran produc tion consisted for ca 50-70% of egg production. The results of this st udy were compared with those from more than twenty other tropical and subtropical waterbodies reported in the literature by deriving empiric al relationships between mean phytoplankton biomass and mean zooplankt on biomass and production. Mean zooplankton biomass and annual zooplan kton production were found to be positively related to mean phytoplank ton biomass, and mean phytoplankton biomass proved to be a good predic tor of mean zooplankton biomass (r(2) = 0.58) and a moderate good pred ictor of annual zooplankton production (r(2) = 0.43). However, the rel ationships between the mean phytoplankton biomass and zooplankton P/B were not significant neither for small-bodied and large-bodied cladoce rans nor for copepods.