Materials used in this work were collected during BIOM ASS - SIBEX project in the Drake Passage and the Bransfield Strait (1983/1984) in three water layers: 0 - 100 m, 100 — 300 m and 300—500 m. Four species of Chaetognatha were found: Eukrohnia hamata and Sagitta gazellae in both water regions; Sagitta planctonis occurred mainly in the Drake Passage whereas Sagitta marri was noted in the Bransfield Strait and adjacent parts of the Bellingshausen and Scotia seas. Chaetognatha were most numerous in the Drake Passage and generally in the layer 100 — 300 m. Vertical distribution of Chaetognatha was clearly influenced hydrological conditions.
Material for this paper was collected during the BIOMASS-SIBEX research programme, and consisted of 97 samples taken at 47 stations in Drake Passage and Bransfield Strait (Antarctica). The samples were taken by hauling Nansen nets vertically through the 0-100, 100 - 300 and 300 - 500 m layers at the end of December 1983 and the beginning of January 1984. Four Chaetognatha species were recorded in the study region: Eukrohnia hamata, Sagitta gazellae, Sagitta mari and Sagitta planctonis. The population structures of the dominant species E. hamata and also S. gazellae were analyzed in the context of the region's hydrology. Certain regularities are apparent in the distribution of the developmental stages of E. hamata in water column. Mature specimens of this species inhabit deeper waters than juveniles. The highest proportions of juveniles in the entire population of E. hamata were recorded in slightly warmer waters.