Distribution pattern of macrozooplankton along the 140°E meridian in the Southern Ocean during austral summer 2002 and 2003

Field surveys were conducted along 140°E in the Southern Ocean north of Terre Adelie during three cruises: the KH cruise by RV Hakuho Maru, and TC1 and TC2 cruises by RV Tangaroa during the austral summers of 2002 and 2003. Macrozooplankton were sampled using a Rectangular Midwater Trawl (RMT 8: mesh size: 4.5mm; effective mouth area: 8m2) along each transect. Macrozooplankton communities were separated by the Southern Boundary of the Antarctic Circumpolar Current (SB-ACC) based on cluster analysis. North of the SB-ACC, macrozooplankton assemblages comprised species of the northern oceanic community characterized by Salpa thompsoni, Euphausia frigida and Themisto gaudichaudii, while south of the SB-ACC, macrozooplankton assemblages were numerically dominated by Euphausia superba and/or Euphausia crystallorophias. It is suggested that the SB-ACC functions as the major biogeographic barrier to separate the macrozooplankton communities, and the contributions of macro- and meso-zooplankton to total zooplankton abundance varies seasonally as well as regionally in the Indian sector of the Southern Ocean crossing the SB-ACC.