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

Abstract

Spatio-temporal variability of zooplankton community structure off east Antarctica (90 to 160° E) was studied from 1988 to 1996 based on samples collected by the Japanese icebreaker 'Shirase'. Three community groups with distinctive species compositions were obtained by cluster analysis. Group 1 was defined as the 'Subantarctic community' because it appeared exclusively 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 Cir- cumpolar Current (ACC), and are thus defined as the 'ACC communities'. All indicator species for Group 2b, including large copepods, Calanoides acutus, Calanus propinquus and Metridia gerlachei, were also common indicators for Group 2a. In Group 2a, smaller copepods (small calanoids, cyclo- poids and poecilostomatoids) and non-copepod herbivores were also indicators. Total abundance was markedly high in Group 2a, and copepods numerically dominated all 3 groups (>70% in Group 1, >80% in 2a, >90% in 2b). The longitudinal distribution pattern of Groups 2a and 2b varied between years, although they occurred along the same latitude. Multiple-regression analysis on environmen- tal variables and distribution of the groups demonstrated that Group 2a tended to occur in relatively warm water masses with high chlorophyll a and low silicate concentrations. While Group 2b occurred in colder areas with low chlorophyll a concentrations, the results of this study suggest that the occa- sional intrusion of northern water further south caused by meandering of the ACC might have been responsible for the observed distribution patterns of the zooplankton community.