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 finmarc hicus is proposed. Female growth and egg production are represented by 8 state variables (gut content, nutrient pool, structural body, oil s ac, and 4 stages of oocyte maturation) which are regulated by physiolo gical processes. Clutch size is set constant under continuous food con ditions, but the spawning interval changes with food availability and temperature depending on the rate of oocyte maturation. Smaller clutch es can occur when eggs are released under bad external conditions. Thu s 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 w ith 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 unavaila ble, the most advanced oocytes are released and egg production continu es until the nutrient pool decreases below a minimal critical value. T hereafter, no eggs are laid. When food reappears, somatic growth resum es until structural body weight is restored, then oogenesis is fuelled . Experimental results were simulated correctly without using matter f rom the lipid pool.