Life-Cycle Strategies and Impact of Cannibalism in Calanoid North Sea Copepods

There were strong differences in life-cycles of dominant calanoid copepod species in the German Bight, although they show a similar seasonal course of abundance and reproduction. In a field study, stage-specific abundances, egg production rates, proportion of spawning females and hatching success of Acartia clausi, Temora longicornis, Centropages hamatus and C. typicus were estimated. The strategy of ceasing reproduction and hibernation of adult females (A. clausi) competed successfully with reproduction throughout the year combined with the production of resting eggs (T. longicornis), or with a strategy of virtual absence in winter and population built-up in spring by nauplii emerging from resting eggs (C. hamatus).In laboratory experiments, feeding rates of females on young copepod offspring were determined. The experiments showed the capability of adults to ingest eggs and nauplii. Predation was strongly influenced by prey density, behaviour of predator and prey, and concentration of alternative food. A theoretical approach demonstrated the potential of such predation to reduce the population sizes markedly during times of intense breeding.