Spatio-temporal variability of zooplankton community structure off east Antarctica (90 to 160 degrees E)

Spatio-temporal variability of zooplankton community structure off east Ant arctica (90 to 160 degrees E) was studied from 1988 to 1996 based on sample s collected by the Japanese icebreaker 'Shirase', Three community groups wi th distinctive species compositions were obtained by cluster analysis. Grou p 1 was defined as the 'Subantarctic community' because it appeared exclusi vely north of the Polar Front, and indicator species of the group included Eucalanus longiceps and Limacina retroversa, which are typical subantarctic species. Groups 2a and 2b occurred in the Antarctic Circumpolar Current (A CC), and are thus defined as the 'ACC communities'. All indicator species f or Group 2b, including large copepods, Calanoides acutus, Calanus propinquu s and Metridia gerlachei, were also common indicators for Group 2a. In Grou p 2a, smaller copepods (small calanoids, cyclopoids and poecilostomatoids) and non-copepod herbivores were also indicators. Total abundance was marked ly high in Group 2a, and copepods numerically dominated all 3 groups (>70% in Group 1, >80 % in 2a, >90 % in 2b). The longitudinal distribution patter n of Groups 2a and 2b varied between years, although they occurred along th e same latitude. Multiple-regression analysis on environmental variables an d distribution of the groups demonstrated that Group 2a tended to occur in relatively warm water masses with high chlorophyll a and low silicate conce ntrations. While Group 2b occurred in colder areas with low chlorophyll a c oncentrations, the results of this study suggest that the occasional intrus ion of northern water further south caused by meandering of the ACC might h ave been responsible for the observed distribution patterns of the zooplank ton community.