Zooplankton of Lake Kivu

The dominant species of the crustacean plankton in Lake Kivu are the cyclopoid copepods Thermocyclops consimilis and Mesocyclops aequatorialis and the cladoceran Diaphanosoma excisum. Mean crustacean biomass over the period 2003-2004 was 0.99 g C m-2. The seasonal dynamic closely followed variations of Chl a concentration and responded well to the dry season phytoplankton peak. The mean annual crustacean production rate was 23 g C m-2 y-1. The ratio between herbivorous zooplankton production and particulate primary production allowed estimating a mean trophic transfer efficiency of 6.8 % between phytoplankton and zooplankton, indicating a coupling between both trophic levels similar to that in other East African Great lakes. These observations suggest a predominant bot-tom-up control of plankton dynamics and biomass in Lake Kivu. Whereas the present biomass of crustacean plankton in Lake Kivu is comparable to that of other African Rift lakes, the zooplankton bio-mass before Limnothrissa introduction was 2.6 g C m-2, based on es-timation from available historical data. So, if the sardine introduction in the middle of the last century led to a 3-fold decrease of zooplankton biomass, it did not affect zooplankton production to a level which would lead to the collapse of the food web and of the fishery.