Comparative structure of the macrozooplankton/ micronekton communities of the Subtropical and Antarctic Polar Fronts

Abstract

The composibon, distribution, abundance, biomass and size-structure of macroplankton/ mcronekton communities at the Subtropical Convergence (STC) and the Antarctic Polar Front (APF) regions were investigated dunng the South African Antarctic Manne Ecosystem Study (SAAMES 11, January-February 1993; SAAMES 111, June-July 1993) A total of 115 and 32 macroplankton/micronekton species were found in the epipelagic zones of the STC and APF, respectively. Cluster analysis based on species composition indicated the occurrence of 3 different plankton communities: one in the STC region, another to the north of the APF and the third to the south of the APF Although the APF and the STC were investigated in dfferent seasons, average abundance and biomass were sirmlar in both regions. Tunicates, euphausiids, decapods and myctophiid fishes dominated the total stock of the 2 frontal regions, in terms of both abundance and biomass Both fronts exhibited considerable fluctuations in the abundance and biomass levels which appeared to covary with the spatial distribution of the phytoplankton stock in the area. The dominant sue-classes were composed of a small group of 5 to 30 rnnl siphonophores, tunicates and euphauslids and a larger group of 40 to 80 mm euphausiids, chaetognaths, vertically-migrating decapods and myctophiid flshes.