Vertical profiles of zooplankton community structure in Prydz Bay, Antarctica, during the austral summer of 2012/2013

The abundance and vertical distribution of zooplankton in the mesopelagic zone are important to better understand their role in carbon and energy transfer in the Southern Ocean ecosystem. In the austral summer of 2012/2013, in Prydz Bay, Antarctica, the vertical profiles of zooplankton community structures between 0 and 1500 m were investigated by multivariate analysis of samples collected using a Hydro-Bios MultiNet (200-A mu m mesh, 0.5 m(2) mouth size). Four zooplankton communities belonging to distinct water strata were identified. Group 1 contained samples collected from the surface water strata (< 100 m) of four shelf and neritic stations. Group 2 was composed of samples collected from the neritic and shelf regions (< 500 m) and the upper layers (0-200 m) of the oceanic region. Group 3 mainly comprised samples collected from the mesopelagic and upper bathypelagic zones (200-1500 m) of shelf and oceanic stations north of the shelf break edge. Group 4 consisted of samples in the 1000-1500 m water stratum of three oceanic stations. The four groups differed more in animal abundance than in species composition. Similarity percentage analysis (SIMPER) showed that zooplankton communities in the upper depth strata (0-200 m) had higher abundance and more pronounced dissimilarity within samples than those below 200 m. A few species (Metridia gerlachei, Rhincalanus gigas, Alacia spp.) showed significant diel vertical migration based on quadratic regression analysis. Sampling depth was the strongest differentiating factor between samples. These results suggest that depth-related differences in environmental characteristics of water masses, such as temperature and salinity, may have the greatest effect upon community structure.