Grazing of Calanus helgolandicus on Dinophysis norvegica during bloom conditions in the North Sea: evidence from investigations of faecal pellets

Toxic dinoflagellate blooms are a common phe- nomenon in the North Sea, but the fate of the toxins in the food web is largely unknown. Herbivorous copepods may play a key role in the transport of toxins through the food web, but it is still uncertain to what extent toxic algae are grazed. The present experiment was carried out during an autumn bloom of Dinophysis norvegica in the North Sea, to study whether Calanus helgolandicus feed on Dinophysis spp. under natural conditions. The experiment showed that C. helgolandicus fed very efficiently on D. norvegica at high algal concentrations (>9000 cells l -1 ), as 98% of the faecal pellets (FP) produced contained Dinophysis spp. cells (up to 32 cells FP -1 ). Therefore, C. helgolandicus feeds on D. nor- vegica under natural conditions, and its FP may be an im- portant vehicle transferring toxins within the pelagic and to the benthic community.