Population dynamics and production of Daphnia carinata (King) and Simocephalus exspinosus (Koch) in waste stabilization ponds

The population dynamics and production of D. carinata and S. exspinosus were investigated in two adjacent maturation-type waste stabilization ponds in South Australia. Population parameters (b', r', and d') for both species were determined from population density, brood size, and egg-development time. Length-weight relationships were determined for both species. Growth of D. carinata was investigated experimentally. Net production of both species was determined using Edmondson's population turnover- time model. Production of D. carinata was also determined using Winberg's biomass turnover model. D. carinata, the numerically dominant species, was a cold water form; high water temperatures increased mortality and reduced growth rate. Both species were food-limited at high population densities. Total annual net production of D. carinata in pond 1 during 1977 (345 g dry wt m-2): calculated using the population turnover-time model, was the highest yet recorded for any planktonic cladoceran. Annual net production of D. carinata determined using the population turnover-time model exceeded annual production determined using the biomass turnover model by 100%. Overestimation of daily production rate was highest during periods of high egg mortality. Total annual net production of D. carinata and S. exspinosus (biomass turnover model) represented a nutrient store equivalent to less than 6% of total PO4-P and total nitrogen retained in the ponds annually.