Mass developments of the cyanobacteria Anabaenopsis and Cyanospira (Nostocales) in the soda lakes of Kenya: ecological and systematic implications

Abstract

The food web of the saline–alkaline lakes of East Africa is characterised by a unique interaction between the Lesser Flamingos as consumer birds and the cyanobacterium Arthrospira fusiformis as the primary producer. However, this interaction is disturbed frequently by alterations of the phytoplankton community. During the period 2001–2012, species of the cyanobacteria Anabaenopsis and Cyanospira were observed in four soda lakes of the African Rift Valley and compared to the entire phytoplankton biomass and composition. Their morphology was highly variable. Each species preferred a distinct range of salinity: C. capsulata 30–40 ppt, C. rippkae 25–35 ppt, A. arnoldii and A. abijatae 10–30 ppt, and A. elenkinii 0–15 ppt. Occasional dominance of Anabaenopsis and Cyanospira in the lakes investigated shows that members of these genera are serious competitors of A. fusiformis, the main food for Lesser Flamingos. Furthermore, mass developments of C. capsulata adversely affected food uptake by the flamingos at Lake Bogoria because they formed mucilaginous colonies that clogged the food filter system. From field samples of the three lakes, uncultured Anabaenopsis and Cyanospira spp. clones were obtained and subjected to phylogenetic analyses. The 16S rRNA gene sequencing data put into doubt the differentiation of Anabaenopsis and Cyanospira into separate genera as recently suggested.