The relationship between the diurnal movements of some of the zooplankton and the sardine Limnothrissa miodon in Lake Kariba, Rhodesia1

Abstract

The numbers of zooplankton at the surface in the open waters of Lake Kariba increased at night. Of the dominant species, the most extensive migrations were shown by adults of Mesocyclops leuckartii ; their nauplii did not show any distinct diurnal movements. Bosmina longirostris exhibited similar, but lesser, movements. Keratella tropica, Keratella cochlearis, and Trichocerca chattoni remained more or less static in the epilimnion throughout the study. For some months after turnover, certain zooplankters move from the floor of the lake to the surface (60 m) each day. When temperature stratification in the monomictic lake intensifies and the hypolimnion becomes devoid of oxygen, these migrations are limited to the depth of the thermocline. These movements are similar to those of the Tanganyika sardine Limnothrissa miodon.