In the planktonie material collected using a Nansen net (vertical hauls) larvae of two euphausiid species were found. The dominant and occurring in all stations were larvae of Thysanoessa macrura. Following larval stages were encountered: nauplius, metanauplius, calyptopis I and calyptopis II. The most numerous and occurring in the widest depth spectrum were calyptopes I. Only twice furcilia VI of Euphausia superba were found. The distribution of euphausiid larvae was influenced by the stratification and circulation of water masses in the investigated area.
In the plankton samples, collected with a Nansen net in three water layers downwards to a depth of 500 m, larvae and eggs of Euphausia superba were found as well as the larvae of E. crystallorophias and E. frigida. Eggs of the species E. superba predominated and among the larvae most numerous were calyptopis I and metanauplius stages. Eggs and larvae of E. superba occurred in small quantities, mainly in Bransfield Strait. Larvae of E. crystallorophias were found in the southeastern part of Bransfield Strait. Metanauplius, calyptopis I and II stages were predominant. Larvae of E. frigida, mostly calyptopis I stage, were very scarce and occurred only at the stations located in Drake Passage.
Krill population structure was studied in Western Antarctic in austral spring and summer 1986/87. At the end of October and the beginning of November in the waters around Elephant Island the mean krill length was 44 mm and sexually mature specimens dominated. Juveniles were absent. In the Bransfield Strait the mean E. superba length was 43 mm. and males slightly overdominated females. The share of females with spermatophores and of immature females was higher than in the Elephant Island area. Juveniles were also not recorded. Krill was most diversified around Elephant Island in January; juveniles and females with ovaries filled with eggs were recorded. It was found that 84% of krill population was infested by ciliate protozoans (Apostomatida).
In the plankton samples collected with a Bongo net besides Euphausia superba the following species of the Euphausiacea were found:. £. frigida, crystallorophias, E. triacantha and T. macrura. The most aboundant and most frequently caught species was T. macrura equally distributed throughout the research area. The species E. frigida also occurred regularly though in much smaller numbers. E. triacantha occurred sporadically, mainly in the western part of the research region, and E. crystallorophias only at two stations in the Bransfield Strait. Some aspects of the biology and ecology of the mentioned above species are presented in this study.
Zooplankton in the water column from the surface to bottom was studied. Copepods were the dominating organisms. Average zooplankton biomass was about 5 g in 1000 m3 . The highest zooplankton density occurred between 300 and 600 m. The influence of the Scotia Front on the horizontal and vertical distribution of zooplankton is discussed.
Macrozooplankton was caught at 17 stations with a Bongo net from the 0-200 m layer. The stations were located near the pack ice edge, between Elephant Islands and the South Orkney Islands. The cluster analysis of 58 recognized taxa allowed to distinguish three regions: the western — near Elephant Island, the middle and the western one — at the South Orkney Islands. No clear difference in macrozooplankton species composition at the open sea stations and those near pack ice was found. The average biomass of macrozooplankton in the investigated area amounted to 82.8 g/1000 m3 (95% CL: 47.2-94.2 g/1000m3). Macrozooplankton was dominated by salps and krill. The biomass and 95% confidence limits were 52.0 g/1000 m3 (15.6-59.2 g/1000 m3) and 26.1 g/1000 m3 (8.4-30.4 g/1000 m3), respectively. Differences in the biomass distribution of some taxa in three distinguished regions were observed. Except of salps the biomass of particular taxa caught near the pack ice edge and the same taxa caught in stations distant from this edge were similar. The biomass of salps was evidently higher in most northern stations.
Herve Cove, a small, shallow and partly isolated basin, is strongly influenced by glacial freshwater inlfow, bringing significant amount of mineral suspension. Its mean annual content amounted up to 46 mg dm-3. Sea anemone (Edwardsia sp.), bivalves (Yoldia eightsi, Laternula elliptica and Mysella sp.), amphipods (mostly Cheirimedon femoratus) a well as some species of polychaetes constituted almost 95% of zoobenthos biomass and 90% of abundance. Four different assemblages of benthic invertebrates, with total biomass ranging from 0.002 kg m-2 up to 1.7 kg m-2, were distinguished in this relatively small (about 12 ha) area. It seems that the freshwater impact influences the composition of an assemblage occurring close to the edge of a glacier. Relatively rich crustacean fauna was encountered in the shallow part of the cove near its entrance. Almost complete lack of echinoderms in Herve Cove, that are common in the shallow Antarctic sublittoral, should also be noted. Macrozooplankton of Herve Cove was dominated by Copepoda. The most frequent and abundant species were: Oithona similis, Ctenocalanus citer and Metridia gerlachei. Far less numerous Chaetognatha represented by three species, Ostracoda, Polychaeta, Pteropoda and Siphonophora constituted only 2.5% of all planktonie animals collected.
In the investigated area krill occured in low abundance. It was recorded mainly above the shelf and above the continental slope close to the Palmer Archipelago and near the northern shores of Elephant Island. In the central part of the Bransfield Strait E. superba was caught in especially small quantities. In general krill of small size occurred, the size decreasing from the west to the east. Mature krill was dominan in the western part of the investigated area, whereas juveniles in the eastern part. Gravid females were caught very rarely.
Macrozooplankton was collected at 63 stations by means of a Bongo sampler in the layer from the surface to a depth of 200 m. Wet formalin volume of siphonophors, polychaetes, pteropods, copepods, amphipods, euphausiids, chaetognaths, salps, and the remaining animals was determined; the distribution of major species was presented. Low diversity in macrozooplankton composition was observed in the study area. As far as biomass was concerned, salps predominated in the whole area; they occurred in exceptionally large quantities Large amounts of krill were also observed in some areas. Besides salps and krill, other euphausiids had the greatest share in the zooplankton; they were more abundant than copepods. Macrozooplankton biomass without salps and krill was low when compared with the values known from literature.