Seasonal variations of phytoplankton species in L ake V ictoria and the influence of iron and zinc ions on the dominant species identified during 2006–2007 studies

The current study was conducted for 2 years (2006 and 2007) during January, April and September to investigate seasonal variations in biological parameters and planktonic biodiversity observed at four sampling sites ( MRM , M 500, SRM and S 500) in L ake V ictoria. Blue‐green algae ( C yanophyta) dominated the lakeshore waters of L ake V ictoria, comprising 54.1% of the total algal content, compared to 24.4% for diatoms and 14.7% for green algae ( C hlorophyta). Euglenophytes and dinoflagellates both constitute <10% of the algal biomass. The algal distribution at the S ango B ay sampling sites, however, is different in that it is dominated by diatoms, in contrast to M urchison B ay, which was dominated by blue‐green algae. This study also investigated the influence of iron ( F e 2+ and F e 3+ ) and zinc ( Z n 2+ ) ions on four strains of microcystis ( CYN 464, CYN 465, CYN 478 and CYN 522) isolated from M urchison B ay in L ake V ictoria. The suggestion that iron species and zinc ions might limit phytoplankton growth in L ake V ictoria was tested by enriching algal culture media with different metal concentrations. Based on measurements of the algal biomass of four species of L ake V ictoria, the algal biomass of the four microcystis strains generally decreased with increased zinc and F e 2+ concentrations. The algal biomass of the four strains, however, increased with increased F e 3+ concentrations. This response to different metal concentrations provides evidence that high Z n 2+ and F e 2+ ion concentrations limit phytoplankton growth and species distribution. The availability of F e 3+ ions is an important selective force on L ake V ictoria phytoplankton communities.