Estimation of Phosphorus Metabolic Rates of Daphnia-Galeata Using a 3-Compartment Model

Abstract

A compartment model to estimate the different phosphorus metabolic rates in Daphnia galeata is presented. The model has three compartments: gut, metabolic pool and structural pool. Existing two-compartment models used for carbon and phosphorus turnover in Daphnia do not allow estimation of ingestion and egestion rates. We extended existing two-compartment models with one more compartment, the gut, which allowed us to estimate both the ingestion and the egestion rates. Parameters of the model are estimated from a single experiment of feeding unlabelled Daphnia with P-32-labelled Scenedesmus obliquus. Separate experiments with juvenile and adult daphnids were carried out in order to compare their metabolisms. This model permits a reliable estimation of the different metabolic rates of Daphnia in a single experiment and discriminates clearly between animals of different sizes. [KEYWORDS: Scenedesmus-acutus; food; zooplankton; release; assimilation; ingestion; quality; carbon; dependence; nitrogen]