Horizontal distribution of the copepod Pseudodiaptomus hessei in subtropical Lake Sibaya

SUMMARY. The horizontal distribution of nauplii, C_I-C_III, C_IV-C_v and adult stages of the copepod Pseudodiaptomus hessei within the main basin of Lake Sibaya (27° 20' S, 32° 37' E) is described on the basis of semi-synoptic cruises on 6 August 1971, 28 January 1972 and 11 February 1972. The distribution observed is considered in relation to variations in food availability and water temperature over this homothermal lake. It is concluded that these factors are not primarily responsible for observed patterns of distribution. Rather, wind-induced currents appear to be of major significance in determining horizontal distribution. Stage-related differences in the nature and extent of horizontal redistribution following severe wind are described. A consideration of the vertical distribution of groups of life-history stages over a diel cycle in relation to the direction and relative strength of currents encountered by the copepods within their respective depth ranges provides an explanation for the differences in horizontal redistribution observed.