Community structure of mesozooplankton in the Antarctic polar frontal zone in the vicinity of the Prince Edward Islands (Southern Ocean): small-scale distribution patterns in relation to physical parameters

Mesozooplankton community structure was investigated in four consecutive years from 1996 to 1999, during late austral summer (April/May), in the vicinity of the Prince Edward Islands. Sampling was carried out using a Bongo net with a mouth area of 0.25 m 2 , and fitted with 300 μm mesh. Surveys were of high resolution, with net tows being separated by ±10–20 km. Zooplankton species composition demonstrated a high degree of similarity between net tows, containing a mix of sub-Antarctic and Antarctic species. However, variation in species abundance levels showed that within each year of study the region was characterised by the presence of different zooplankton communities. These communities differed by as much as an order of magnitude in total zooplankton density. Analysis of physical variables indicated that zooplankton communities were associated with different water masses, identifiable by their physical characteristics. Sea temperature was the most important physical variable, accounting for as much as 69% of the variation in community structure. Communities were often not spatially discrete, and many stations demonstrated a high degree of similarity despite wide spatial separation. The heterogeneity in the biological and oceanographic environment extended to a small scale, on the order of 10 km. This is indicative of the oceanographic complexity of the region. The complex oceanography associated with shallow topography, including seamounts, islands, and frontal zones, indicates that small-scale spatial heterogeneity in zooplankton communities may be an important factor to consider when modelling these ecosystems.