The effect of five non-phytoplankton and one phytoplankton diets on reproduction is described for the copepod Calanus helgolandicus and compared to field fecundity estimates. A fecundity increase followed ingestion of larvae of the sea urchin Sphaerechinus granularis (LSU) and the oyster Crassostrea gigas (OYS) by copepod females, whereas a decrease followed ingestion of eggs of the copepods Acartia and Temora spp. (COP), as a function of protein concentration in diets. With larvae of the sea urchin Paracentrotus lividus (SSU) and the dinoflagellate Prorocentrum minimum (PM; standard phytoplankton diet), fecundity was identical. Although protein concentrations differed greatly from one food treatment to the other, mean fecundity values were rather low. For unknown reasons, and despite their very high protein concentrations in comparison to in situ, none of these diets could improve female fecundity or reach maximum egg production rates reported in C.helgolandicus. Hatching rates were >80%, stable and similar with both PM and COP diets. With SSU, LSU and OYS diets, egg viability was lower than in situ and with PM, showing a strong and mild decrease with time with LSU and SSU, respectively. Ingestion of zygotes of the brown alga Fucus spiralis (ZYG) led to the death of females. These results suggest that dense blooms of zygotes of macroalgae and invertebrate embryos and larvae, occurring in the continental shelf as part of copepod diets, could have different effects on the demographic response of C.helgolandicus.