Production biology of copepods and cladocerans in three south-east Sri Lankan low-land reservoirs and its comparison to other tropical freshwater bodies

Production, biomass and productivity of the microcrustacean zooplanktonpopulations of three low-land reservoirs, Tissawewa (eutrophic), Ridiyagama(moderately eutrophic), and Muruthawela (mesotrophic) in South-east SriLanka were studied. The temporal variation of zooplankton production wasstudied in Tissawewa on basis of fortnightly sampling on five fixed samplingstations for 2 years. Zooplankton production was relatively high, mainlybecause of high copepod production predominantly realised due to twocalanoid copepods, Phyllodiaptomus annae and Heliodiaptomus viduus. Abouthalf of the copepod production was contributed by the naupliar instarstages, whereas the contribution of the eggs was generally much smaller(<20%). In contrast, the cladoceran production consisted for ca50–70% of egg production. The results of this study werecompared with those from more than twenty other tropical and subtropicalwaterbodies reported in the literature by deriving empirical relationshipsbetween mean phytoplankton biomass and mean zooplankton biomass andproduction. Mean zooplankton biomass and annual zooplankton production werefound to be positively related to mean phytoplankton biomass, and meanphytoplankton biomass proved to be a good predictor of mean zooplanktonbiomass (r² = 0.58) and a moderate good predictor ofannual zooplankton production (r² = 0.43). However,the relationships between the mean phytoplankton biomass and zooplankton P/Bwere not significant neither for small-bodied and large-bodied cladoceransnor for copepods.