MOLTING AND MORTALITY-RATES OF COPEPODS RELATED TO AGE WITHIN STAGE - EXPERIMENTAL RESULTS

Patterns of copepod mortality and moulting related to age within stage, described by a mathematical model of population dynamics, were tested experimentally on Centropages typicus. Individuals of the same brood were observed separately at regular time intervals from copepodite I to adult, sorted as living or dead, and checked for stage. The results obtained for the pooled copepods enabled a reconstruction of the mean durations of each stage for the whole cohort, and to interpret them with respect to the information acquired for each individual. Probabilities of moulting and dying were not constant but depended on age within stage. In all copepodite stages, the distribution of durations in relation to age within stage was asymmetrical around a mode. A minimum mortality rate (0.01 to 0.02 d-1) was present before the mode of the duration distribution. Beyond the mode, mortality increased up to a maximum of 0. 1 for those individuals which stayed in a stage twice ds long as normal. A conceptual model of moulting and mortality rates during the moult cycle is proposed. Modelling and experimentation suggest that the variable development ot copepods bred from a synchronous cohort does not proceed as a purely random phenomenon, but seems to be determined by the diverse physiological conditions displayed by different members of the same population. We show here that modelling does not only have a quantitative purpose - it should also lead to a better understanding of the phenomena involved.