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(10-08) Direct and indirect effects of nonylphenol on functional groups of a lotic ecosystem . Hulot, Florence*,1, Hélène, Magaud2, Jean-Marc, Bonzom2, 1 Laboratoire Fonctionnement et évolution des systèmes écologiques; Ecole Normale Supérieure - UMR 7625; 46, rue d'Ulm, Paris, France2 INERIS, Unité d'évaluation des risques écotoxicologiques, Verneuil-en-Halatte, France ABSTRACT- Toxic substances may harm sensitive species. However, as the effect can be transmitted through the interactions linking the species, the whole community may be affected. Here we investigated direct and indirect effects of 4-nonylphenol (4-NP) on a lotic ecosystem by comparing experimental results and predictions of a theoretical model. An 16-month mesocosm experiment was conducted to study the effects of 4-NP on a lotic ecosystem. These mesocosms contain sediments, rocks, aquatic plants, periphyton, invertebrate consumers and detritivores, and fish. Two replicates of four levels (0, 0.33, 3.3 and 33 ug/l) of 4-NP were tested in separate channels. The effect of 4-NP on individuals and populations of the ecosystem were measured. We developed a model of the lotic ecosystem based on functional groups defined according to trophic interactions between species. The effects of 4-NP on the various functional groups were analysed by loop analysis, a qualitative method allowing to predict direct and indirect effects of a perturbation on the system variables. The predictions were made according to the assumption that all functional groups are directly negatively affected by 4-NP. This leads to negative, positive or indeterminate indirect effects on the other functional groups. The experimental results show (1) a positive effect of 4-NP on periphyton, (2) a negative effect on gastropod (mainly Lymnea peregra) and (3) no effect on detritivores, zooplankton, Hirudinae and threespine stickleback. These responses suggest that the dynamics of periphyton and of gastropods are respectively more affected by indirect positive effects and direct and indirect negative effects of 4-NP. This work show the importance of the interaction web for the propagation of perturbations. Key words: nonylphenol, direct and indirect effects, mesocosms, food web |
