Egg production rates of Calanus helgolandicus females reared in the laboratory: Variability due to present and past feeding conditions

Four egg production experiments were performed under controlled conditions on Calanus helgolandicus females from laboratory cultures with a known history of feeding conditions. Two of the experiments were run with females from a cohort reared at a low concentration of Prorocentrum micans (77.5 μg C l^-1, Cohort L). One of the egg production experiments was run at the same low food concentration (females called LL) and the other one at high food concentration (females LH). Another 2 experiments were performed with females from a cohort reared at a high P. micans concentration (278 μg C l^-1, Cohort H). One of these experiments was run at the same high food level (females HH) whereas the other one was run at the low food concentration (females HL). These 4 experiments allowed us to estimate the influence of both present and past feeding conditions on the egg production rates of the females. The catabolism of the internal resources in terms of carbon (lipid) and nitrogen (protein) of the females was more important for those held at the low concentration and it also varied with the origin of the females. Females L, which had been food-limited during their growth (LL and LH), were apparently deficient in nitrogen since they lost twice as much carbon as nitrogen, whereas females H (HH and HL) drew equally on their carbon and nitrogen resources. After 7 to 10 d, the egg production of females L was significantly lower than that of females H, at both food concentrations (LL < HL and LH < HH). To explain these results, we propose that females L had a lower assimilation efficiency than females H and that, even if they had a higher specific ingestion rate at the beginning of the experiment, they were not able to compensate for metabolic deficiencies (e.g. in protein). Our results indicate that the feeding history of the females may be important in explaining the egg production values found in the field since in situ food conditions are unlikely to remain optimal during an entire generation.