Growth and egg production of female Calanus finmarchicus: An individual-based physiological model and experimental validation

A detailed individual-based model of egg production of Calanus finmarchicus is proposed. Female growth and egg production are represented by 8 state variables (gut content, nutrient pool, structural body, oil sac, and 4 stages of oocyte maturation) which are regulated by physiological processes. Clutch size is set constant under continuous food conditions, but the spawning interval changes with food availability and temperature depending on the rate of oocyte maturation. Smaller clutches can occur when eggs are released under bad external conditions. Thus changing conditions can produce different clutch size distributions. For model validation, egg production experiments were conducted under different constant and fluctuating food concentrations and compared with model simulations. In the experiments, egg production was strongly affected by food fluctuation. In experiments with alternating feeding and starvation cycles integrated egg production was affected by mean food concentration during the experiment rather than by the frequency of the cycles. The model reproduces correctly the egg production rates and final body carbon of females kept in the different food regimes. It provides a dynamical explanation of physiological responses of the individual under short term food variation. When food becomes unavailable, the most advanced oocytes are released and egg production continues until the nutrient pool decreases below a minimal critical value. Thereafter, no eggs are laid. When food reappears, somatic growth resumes until structural body weight is restored, then oogenesis is fuelled. Experimental results were simulated correctly without using matter from the lipid pool.