ESTIMATION OF PHOSPHORUS RELEASE RATES FROM NATURAL ZOOPLANKTON COMMUNITIES FEEDING ON PLANKTONIC ALGAE AND BACTERIA

Phosphorus release rates from Daphnia galeata, the dominant metazoan, were estimated in eutrophic Lake Nesjovatn during summer by applying o ur previously published mass balance model. For both juveniles (2.0 mu g C ind.(-1)) and adults (6.6 mu g C ind.(-1)), three different estim ates of P release were made by two different parametrizations and by c onsidering the importance of ingestion of detrital particles. As a bas is for estimates of P release, clearance rates of algae and bacteria w ere determined as well as a thorough characterization of the food comp artments. The specific release rate of P varied between 0.16 and 1.18 mu g P mg C-1 h(-1) for juveniles and between 0.06 and 0.96 for adults , independent of estimate. These release rates are considerably lower than those obtained by previously published models. Most of the observ ed variation was due to variation in the P content of the food, thus e mphasizing the importance of including this variable in studies of P r elease from zooplankton. Calculations of rates of population P release suggest that D. galeata contributed <1/3 of the P requirements of alg ae and bacteria.