# Cichlid species diversity in naturally and anthropogenically



## samaki (Oct 25, 2002)

Cichlid species diversity in naturally and anthropogenically turbid
habitats of Lake Victoria, East Africa
Frans Witte • Ole Seehausen • Jan H. Wanink •
Mary A. Kishe-Machumu • Marjolein Rensing •
Tijs Goldschmidt

During the past decades, major anthropogenic
environmental changes occurred in Lake Victoria,
including increased predation pressure due to Nile perch
introduction, and decreases in water transparency and
dissolved oxygen concentrations due to eutrophication.
This resulted in a collapse of the haplochromine cichlids
in the sub-littoral waters of the Mwanza Gulf in
1986-1990, followed by a recovery of some species in the
1990s and 2000s, when Nile perch densities declined.
We studied two data sets: (1) haplochromines from
sand and mud bottoms in the pre-collapse period; (2)
haplochromines from sub-littoral areas during the precollapse,
collapse and recovery periods. Water over mud
is murkier and poorer in oxygen than water over sand, and
differences in haplochromine communities in these natural
habitats during the pre-collapse period may predict the
effects of anthropogenic eutrophication during the collapse
and recovery periods. In the pre-collapse period,
haplochromine densities over sand and mud did not differ,
but species richness over sand was 1.6 times higher than
over mud bottoms. Orange- and white-blotched colour
morphs were most common at the shallowest sand station.
More specifically, insectivores and mollusc-shellers had
higher numbers of species over sand than over mud,
whereas for mollusc-crushers no difference was found.
Laboratory experiments revealed that mollusc shelling was
more affected by decreased light intensities than mollusc
crushing. During the pre-collapse period, spawning
occurred year-round in shallow areas with hard substrates
and relatively clear water. In deeper areas with mud bottoms,
spawning mainly occurred during months in which
water clarity was high. No effects of hypoxia on spawning
periods were found. It follows that clearer water seems to
support differentiation in feeding techniques as well as
year-round spawning, and both may facilitate species
coexistence. Water clarity is also known to be important
for mate choice. These observations may explain why,
since the decline of Nile perch, haplochromine densities
have recovered, the numbers of hybrids increased and
species diversity in the current eutrophic sub-littoral
waters has remained 70 % lower than before the environmental
changes.

F. Witte (&)  J. H. Wanink  M. A. Kishe-Machumu 
M. Rensing  T. Goldschmidt
Institute of Biology Leiden, University of Leiden,
P.O. Box 9505, 2300 RA Leiden, The Netherlands
e-mail: [email protected]
F. Witte
Netherlands Centre for Biodiversity, Naturalis,
P.O. Box 9517, 2300 RA Leiden, The Netherlands
O. Seehausen
Department of Aquatic Ecology and Evolution,
Institute of Ecology and Evolution, University of Bern,
Baltzerstrasse 6, 3012 Bern, Switzerland
O. Seehausen
EAWAG Centre for Ecology, Evolution and Biogeochemistry,
Seestrasse 79, 6047 Kastanienbaum, Switzerland
J. H. Wanink
Koeman en Bijkerk bv, Ecological Research and Consultancy,
P.O. Box 111, 9750 AC Haren, The Netherlands
M. A. Kishe-Machumu
Tanzania Fisheries Research Institute, Dar es Salaam Center,
P.O. Box 78850, Dar es Salaam, Tanzania
Aquat Sci (2013) 75:169-183
DOI 10.1007/s00027-012-0265-4 Aquatic Sciences
123


----------

