Fottea, Olomouc, 15(2): 245–257, 2015 245 DOI: 10.5507/fot.2015.012 Algal communities of Kenyan soda lakes with a special focus on Arthrospira fusiformis Michael Schagerl 1* , Alfred Burian 2 , Martin gruBer–Dorninger 1 & Steve O. oDuor 3 , Mary N. Kaggwa 4 1 University of Vienna, Department of Limnology and Bio–Oceanography, Althanstrasse 14, A–1090 Vienna, Austria; * Corresponding author e–mail: Michael.schagerl@univie.ac.at 2 Stockholm University, Department of Ecology, Environment and Plant Sciences, Sweden. 3 Egerton University, Department of Biological Sciences, Kenya. 4 University of Rwanda, Nyagatare Campus, Rwanda. Abstract: Soda lakes are simple in biodiversity, but due to their highly stochastic environmental dynamics unexpected shifts in species composition do occur. We studied key drivers for structuring phytoplankton communities and identifed variables signifcantly infuencing changes of Arthrospira fusiformis abundance in the Kenyan soda lakes, Nakuru and Bogoria. In both lakes, Arthrospira fusiformis dominated algal biomass, but in Nakuru, crashes of this taxon were recorded. The three variables sodium, pH and dry mass signifcantly contributed to the phytoplankton taxa pattern. Arthrospira was absent at highest turbidity and salinity levels, being outcompeted by the small, single–celled chlorophyte Picocystis salinarium. Picoplankton was in general connected to higher pH values and tended to occur anti–cyclic to Arthrospira. Overall, the abundance of A. fusiformis was infuenced by the boundaries of habitat suitability, light penetration, grazers and cyanophages attacks. Keywords: Biological, environmental, phytoplankton, saline–alkaline, salinity, Spirulina, cyanophage, virus IntroductIon Arthrospira fusiformis (Voronichin) KomáreK et lunD (formerly called Spirulina plantensis Voronichin) is a filamentous cyanobacterium which occurs worldwide with a preference in tropical soda lakes (Table 1) and is capable of adaptation to a varied range of habitats, from freshwater–alkaline conditions to saline–alkaline and even hypersaline environments (ciferri 1983; Da- Dheech et al. 2010). In the soda lakes of East Africa, Arthrospira fusiformis (hereinafter referred to as Ar- throspira) forms an exceptionally high algal crop due to its high photosynthetic capacity turning these lakes to one of the world’s most productive ecosystems (Ta- lling et al. 1973; melacK & Kilham 1974; oDuor & Schagerl 2007a). It is the main food for the Lesser Flamingos, Phoeniconaias minor geoffroy, that flock these lakes in millions (VareSchi 1978; KrieniTz & KoTuT 2010). The endorheic soda lakes are prone to hydrolo- gical influences since they are often located in semi– arid regions, and their levels can fluctuate considerably in response to seasonal changes and annual differences in rainfall (melacK 1981). The dependence on phyto- plankton as driving force of productivity is even gre- ater in these extreme habitats compared to freshwater systems since they have minimal macrophyte growth and low allochthonous organic carbon input due to li- mited surface run–off and river–inflows (Burian et al. 2014). The dense phytoplankton, high amounts of di- ssolved organic matter (JirSa et al. 2012) and increased particle loading significantly reduce the contribution of micro–phytobenthic community to overall productivi- ty due to the resulting poor light climate in the water column (oDuor & Schagerl 2007b). Several studies have been conducted on the al- gal communities prevailing in African saline lakes (e.g. KrieniTz et al. 2003; BalloT et al. 2005; Schagerl & oDuor 2008; KrieniTz & KoTuT 2010; Kaggwa et al. 2012), where temporal trends have often indicated pe- riodic dominance and absence of certain taxa especi- ally at extreme salinity. Apart from the predominant Arthrospira, also other cyanobacteria occur in these lakes. The most important are Anabaenopsis arnoldii apTeKarJ, Anabaenopsis abijatae KeBeDe et willen, Synechococcus minutus Voronichin, Haloleptolyng-