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.
The biology and ecology of an Antarctic species Oncaea antarctica, which belongs to the Cyclopoida, was reconstructed from analyses of vertically-stratified zooplankton sets of samples taken with a 150 *m and 250 *m-mesh net during the day and at night, during 3 austral seasons (sum-mer - December 1985, autumn - April 1988, winter - June-August 1989). The plankton material was collected at stations located in Croker Passage (Antarctic Peninsula). Inhabiting meso- and bathypelagic waters, O. antarctica was one of the most numerous cyclopoids of the family Oncaeidae, making up 50% of all Cyclopoida in winter. Females carrying egg sacs and copulating pairs of this species were present during all three seasons investigated.
Owing to their large numbers, small Calanoida from the Pseudocalanidae family constitute a significant element of zooplankton in seas and oceans. In Croker Passage, which is in the coastal zone of the Antarctic Peninsula, this family is represented by Microcalanus pygmaeus and Ctenocalanus citer. These species are characterized by a distinct seasonal variability in numbers and by the way they inhabit the water column. M. pygmaeus occurs five to six times more frequently than C. citer, and both species are far more abundant in summer than in winter. In summer they occur in the upper part of the mesopelagic zone, while in winter they move to greater depths. However, C. citer occurs more often than M. pygmaeus in the upper layers of the water column, regardless of season.
This paper focuses on the diatom flora of Moss Creek in Antarctica that was collected during two summer (1995/96 and 2001/02) seasons. Of the 95 taxa identified in Moss Creek, two groups of diatom communities were distinguished. Achnanthes germainii, Eucocconeis ninckei, and Nitzschia homburgiensis, taxa indicative of unpolluted waters, dominated in the upper course of the creek. The other group was found in the lower reaches of the creek and included taxa indicative of eutrophic environments. In this part of the creek Mayamaea atomus associated with Nitzschia gracilis and Planothidium lanceolatum were dominant. In both sampling periods the species composition of the dominant taxa was similar with the distinct predomination of Mayamaea atomus. During the 1995/96 season, Nitzschia gracilis, N. homburgiensis, and Planothidium lanceolatum also occurred abundantly, whereas in 2001/02 the proportions of Nitzschia gracilis and Planothidium lanceolatum showed a slight increase.