Distribution and community structure of euphausiids in the Southern Ocean along the 140°E meridian during the austral summer 2001/2002

The abundance, biomass, diversity and community structure of euphausiids in the Southern Ocean along the 140°E meridian from latitudes 47°S–65°S were examined by RMT8 from 0 to ca. 1000 m during the 2001/2002 austral summer. Both total abundance and biomass of euphausiids were much higher in the south of the southern branch of the Polar Front (PF-S) located at 60°S–61°S than in the northern part, corresponding with higher chlorophyll a concentrations. Eleven species of euphausiids were collected from the research areas: 2 species of Thysanoëssa, 6 of Euphausia, and a single species each of Thysanopoda, Bentheuphausia and Nematoselis. In Euphausia and Thysanoëssa, clear horizontal distribution patterns enabled the classification of each species into one of 3 different types: species occurring only at stations north of the PF, species occurring in a broad distribution from south of the PF-S to the south of the Southern Boundary (SB) of the Antarctic Circumpolar Current, and species occurring only south of the SB. The latitudinal zonations occurrence and peak abundance were evident for all species. Hierarchical cluster analysis by species and station resulted in the identification of 2 distinct communities of euphausiids: community I comprised the three stations north of the PF where both euphausiid abundance and biomass were relatively low, and 2 species, Thysanopoda acutifrons and Thysanoëssa gregaria dominated, community II comprised the southern five stations where abundance and biomass were high and Euphausia frigida, E. superba and Thysanoëssa macrura were numerically dominant. Among the five oceanographic fronts within the research area, the PF (either south or north) appears to be the important biogeographical boundary separating abundance, biomass, and the community structure of euphausiids.