Community structure of epipelagic macrozooplankton in the
Ross Sea

During the 9th research cruise of the R/V Kaiyo-maru, macrozooplankton samples were collected from three layers between the surface and 200 m with RMT 8m2 along the three longitudinal lines in the Ross Sea and neighboring waters. Biomass and abundance (number of individuals) were 0 ~ 32.1 g/1000m3 and 1.8 ~ 2314.3 inds/1000m3 along 175°E line, 1.6 ~ 23.7 g/1000m3 and 226.4 ~ 3224.0 inds/1000m3 along 180°, and 0.1 ~ 8.5 g/1000m3 and 46.8 ~ 619.7 inds/1000m3 along 170°W. Biomass and abundance were extremely low at stations on the continental shelf along 175°E and 170°W except the southern most station located at 78°S, 175°E. Total of 13 taxa occurred at all stations and mean of 7.4 taxa were occurred in each sample. There was no marked difference in numbers of taxa occurred at each station and layer except at 0 ~ 50 m of 72°S, 175°E, where euphausiids only occurred. Copepods and chaetognaths dominated in the north of 72°S, while pteropods and euphausiids occurred besides them in the south of 72°S along 175°E. Pteropods comprised high percentage of total abundance at the southernmost stations along 175°E and 170°W. Stations and layers were categorized into four major groups by cluster analysis based on taxonomic composition. The group 1 comprised of stations with bottom depth of deeper than 1000 m (in the north of 72°S along 175°E) and group 2 to 4 on the continental shelf. The latter three groups are characterized by copepods + chaethognaths + euphausiids, pteropods + euphausiids and pteropods. These were overlapped geologically with different group(s) at different layer(s).