Mesoscale distribution of zooplankton around South Georgia

A net sampling survey was conducted around the island of South Georgia in the austral summer 1981/1982 and again in winter 1983. This paper uses Principal Components Analysis to elucidate the mesoscale features of zooplankton distribution within the two survey grids. During both surveys the major contrast was between the plankton of the shelf and the surrounding ocean. However, within the oceanic part of each grid, localized areas of warmer water were inhabited by a fauna characteristics of warmer latitudes to the north. The biological and oceanographic evidence suggests that areas represents core rings or similar intrusions from north of the Polar Front. Not all of the characteristic warm- and cold-water species showed a clear correlation with water origin. For example, the swarming behaviour of Euphausia superba limited its usefulness as a mesoscale tracer. Likewise, the distribution of the Antarctic copepod Calanoides acutus was poorly related to water temperature during the summer survey because the timing of sampling coincided with its annual spawning cycle. Large-scale movement of oceanic fronts has already been identified as being important in dictating overall species composition around the island, but at a smaller scale these intrusions of warmer water may be an important intermediary mechanism of community advection into the area.

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