Phycotoxins synthesized by benthic dinoflagellates are known to bioaccumulate in macrofauna and hence represent a risk for human health. However, the presence of toxins synthesized by benthic dinoflagellates in smaller marine organisms than macrofauna has not been considered despite the fact that such small organisms have an important ecological role in the benthic food web. This present study quantified, for the first time, the trophic relationship between benthic dinoflagellates and meiofauna by using stable isotope enriched dinoflagellates during ingestion experiments. Results showed that harpacticoid copepods were not able to discriminate, during ingestion, between the potentially toxic cells of Ostreopsis cf. ovata and the non-toxic cells of Amphidinium cf. carterae, even when another food resource, such as diatoms (e.g. Odontella sp.), was provided (Kruskal Wallis test, p > 0.05).