THE RECENT STATUS OF PHYTOPLANKTON COMPOSITION AND BIOMASS
IN SOUTHERN LAKE VICTORIA (TANZANIA)
Pazi M. Semili
PhD Student, Faculty of Aquatic Sciences and Technology, UNIVERSITY OF DAR ES
SALAAM, TANZANIA. P.O.Box 35064, Dar es Salaam. Email: pmwinyimvua@yahoo.co.uk.
Abstract
Phytoplankton form the basis of both fresh water and marine food web, and the organic
compounds excreted also stimulate bacterial growth. However, despite their crucial
importance, over growth of phytoplankton and toxin-producing species may seriously
disrupt the food web and lead to fish kills and human poisoning. Toxic phytoplankton
blooms may further devaluate ecosystem deliverables such as fish production, drinking
water supply or recreational use. Lack of understanding of future climate, ecosystem
functioning and its response to climate change and nutrient inputs calls for a continued
scientific effort to improve our knowledge on present day Lake Victoria ecosystem
functioning and its resilience. This paper presents the recent status of phytoplankton
species composition and biomass in southern Lake Victoria 9Tanzania). Water samples
were collected monthly for a period of 8 months (December 2005 to July 2006), using Von
Dorn sampler. Phytoplankton species composition and biomass were determined in the
laboratory using Utermöhl method under LEICA DMIL inverted microscope. The study
indicated that Cyanobacteria (blue green algae), Diatoms, Green algae, Cryptomonads and
Dinoflagelates were the main phytoplankton groups during the study period. In overall,
Cyanobacteria dominated other algal species. Average total algal abundance and biomass
were approximately 4 times higher in the inshore shallow regions than in offshore.
Improved light conditions and high nutrients concentration in inshore shallow regions
boost the development of algal biomass, including toxin producing species such
Microcystis and Anabaena. Assessment of the current and published information on
phytoplankton composition at both inshore and offshore regions confirms the eutrophic
nature of Lake Victoria. Dominance of blue green algae including toxin producing species
may have negative implications on water quality and fisheries production. Therefore, there
is need to take measures to avert rampant of the water environment for sustainable fishery
production and, for clear and safe water supply.
Key word: Lake Victoria, phytoplankton, fish kills, toxin-producing species.
NB:
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