Population structure analysis of five of the most abundant Calanoida species showed their life strategy to be highly individual, even between animals belonging to the same trophic levels. In phytophages, such as C. acutus, sex determination began in autumn, earlier in females than in males. Males generally, rather low in abundance, were present for a relatively short time of the year. They occurred in the deepest part of the water column, where fertilisation should take place. A similar pattern of reproductive peaks was observed in C. propinquus, though males were not so scarce as in the former species and adults were present in the entire water column, so fertilisation was possible everywhere. The population of R. gigas showed the presence of two generations per year. Females pre-dominate among adults. In summer, fertilisation occurred in the epipelagic water layer, while in winter it descended to the bathypelagic water. In M. gerlachei sex determination seems to be an ongoing process. Fertilisation takes place in the deepest part of the water column, thus indicating the bulk presence of males, while females were distributed nearly evenly throughout the water column, except for the surface layers. E. antarctica - a predator - started to breed in winter. The predominant females were often ob-served with a few spermatophores; this suggests that females can survive longer than males.