Reproductive success in Calanus helgolandicus as a function of diet and egg cannibalism

Calanus helgolandicus females were incubated for 6 to 25 d in single and mixed diets of the diatom Coscinodiscus curvatulus and the dinoflagellate Gymnodinium sanguineum using 2 incubation protocols, and fecundity, hatching success, egg cannibalism and faecal pellet production were measured. Both fecundity and hatching success were significantly reduced by single or mixed diets containing high concentrations of diatoms. The deleterious effect of the diatom was diminished when females were fed diets containing low diatom concentration and also when egg cannibalism represented ca >20% of the total daily egg production. Egg cannibalism was higher with the wheel-incubation method than with the vial-incubation method. The results suggest that diatom inhibition of copepod reproduction can be reduced in various ways, including decreasing the diatom concentration, switching from diatom to dinoflagellate diets, increasing the diversity of food items and also by egg cannibalism (eggs are of high nutrient value).