Harmful algal blooms and spatio-temporal variability of microcystins in Nyanza Gulf, Lake Victoria

Session: Harmful Algal Blooms: From Ecosystem Drivers to Ecosystem Impacts (2)

Lewis Sitoki, The Technical University of Kenya, [email protected]

Abstract

Occurrence of harmful algal blooms, microcystin (MC) concentrations, plankton community composition and environmental conditions were investigated to characterize the trophic status of Nyanza Gulf between 2007 and 2011. The study showed increased eutrophication in Kisumu Bay and the two central stations of the gulf with a drastic reduction in transparency, changes in phytoplankton composition and increased nutrient concentrations. The dominating group of phytoplankton in the gulf was cyanobacteria, usually associated with harmful effects whereas diatoms were more important at Rusinga channel and the main lake station. In the gulf Microcystis accounted for the largest part (> 50 ? 90 %) of cyanobacterial biovolume with two highly toxic tropical species (Microcystis panniformis, Microcystis protocystis) dominating the phytoplankton most of the time in Kisumu Bay. Microcystins (1- 90 µg l^-1) were detected in most of the samples dominated by Microcystis in the gulf stations. Occurrence of MC could only be associated with Microcystis. Eutrophication in Lake Victoria therefore presents one of the most serious ecological problems in addition to making seafood unsuitable for human consumption.