The effects of benthic invertebrates on stoichiometry of the nutrient recycling have received considerable attention in contemporary aquatic ecological research. However, just species-specific effects and trophic-mediated mechanisms (i.e. nutrient excretion) have been addressed up to now, while the contribution of non-trophic effects (i.e. bioturbation) and species interactions were neglected or poorly understood. In laboratory microcosms, we manipulated the number and composition of 3 functionally distinct benthic invertebrate freshwater species (Heteromastus similis – Polychaeta, Heleobia australis – Gastropoda and Chironomus sp. - Insecta) over 3 biomass levels, to test the effects of bioturbator diversity on pelagic C:N:P molar ratios. Invertebrate species richness did not affect significantly pelagic nutrient ratios, but biomass and the interaction between biomass and species richness modified significantly overlaying water C:N, C:P and N:P ratios. The lack of significant effects of bioturbator species richness alone was mainly related to strong overall (i.e. irrespective to biomass) species composition effects on pelagic C:N:P stoichiometry. These results were probably related to a combination of nutrient-specific density dependence and density-mediated interaction strength. We suggest that benthic invertebrate biodiversity may impact benthic-pelagic coupling not only through enhancing the nutrient flux, but also by altering the water column nutrient stoichiometry via complex nonadditive bioturbational interactions.