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JPR Advance Access published online on August 11, 2006
Journal of Plankton Research, doi:10.1093/plankt/fbl032
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© The Author 2006. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oxfordjournals.org
Received April 12, 2006
Accepted July 24, 2006

Article

Zooplankton of Lake Kivu, East Africa, half a century after the Tanganyika sardine introduction

Mwapu Isumbisho 1, Hugo Sarmento 2, Boniface Kaningini 3, Jean-Claude Micha 2, and Jean-Pierre Descy 2 *

1 Unite D’Enseignement et de Recherche en Hydrobiologie Appliquee (UERHA), ISP/Bukavu, B.P. 854-Bukavu, Democratic Republic of Congo; Laboratory of Freshwater Ecology, URBO, Department of Biology, University of Namur, B-5000 Namur, Belgium
2 Laboratory of Freshwater Ecology, URBO, Department of Biology, University of Namur, B-5000 Namur, Belgium
3 Unite D’Enseignement et de Recherche en Hydrobiologie Appliquee (UERHA), ISP/Bukavu, B.P. 854-Bukavu, Democratic Republic of Congo

* To whom correspondence should be addressed.
Jean-Pierre Descy, E-mail: jpdescy{at}fundp.ac.be


  Abstract

The introduction into Lake Kivu of the planktivorous fish Limnothrissa miodon at the end of the 1950s raised major concern about the fate of mesozooplankton, but few data were available to assess the impact of predation. In this study, we followed zooplankton variations in Lake Kivu for 3.5 years. Present Lake Kivu mesozooplankton is dominated by cyclopoid copepods (Thermocyclops consimilis, Mesocyclops aequatorialis and Tropocyclops confinis), but cladocerans and rotifers are also present. Each year, total crustacean abundance in the plankton increased to a distinct seasonal maximum following a rise of phytoplankton production associated with a deep epilimnetic mixing in the dry season (August-September). This dependence on phytoplankton resource suggests that mesozooplankton dynamics in Lake Kivu is mainly bottom-up controlled, contrary to expectations from the food web structure. However, measurements of body size indicates that the sardine predation affects the cladoceran Diaphanosoma excisum, while the larger copepods may efficiently escape predation by migration in the deep mixolimnion at daytime. Total biomass of mesozooplankton in Lake Kivu is lower than in lakes Tanganyika and Malawi. This may be related to the disappearance of a large grazer which existed prior to the sardine introduction, whereas the large lakes of the same region have a more complex pelagic food web, with piscivorous fish, and with calanoid copepods, which can more efficiently exploit phytoplankton production.

Communicating Editor: KJ Flynn


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