Cyanobacteria and cyanobacterial toxins in three alkaline Rift Valley lakes of Kenya—Lakes Bogoria, Nakuru and Elmenteita

Abstract

For decades frequent mass mortalities of Lesser Flamingos (Phoeniconaias minor Geoffroy) have been observed at alkaline-saline Kenyan Rift Valley lakes. To estimate the potential influence of toxic cyanobacteria on these mass deaths, the phytoplankton communities were investigated in Lakes Bogoria, Nakuru and Elmenteita. Cyanobacterial toxins were analyzed both in the phytoplankton from the three lakes and in isolated monocyanobacterial strains of Arthrospira fusiformis, Anabaenopsis abijatae, Spirulina subsalsa and Phormidium terebriformis. Lake Bogoria was dominated by the cyanobacterium A. fusiformis. In L. Nakuru and L. Elmenteita the phytoplankton mainly consisted of A. fusiformis, A. abijatae and Anabaenopsis arnoldii, and in L. Nakuru an unknown Anabaena sp. was also found. Furthermore, this is the first time A. abijatae and the unknown Anabaena sp. have been found in Kenyan lakes. Phytoplankton wet weight biomass was found to be high, reaching 777 mg L 1 in L. Bogoria, 104 mg L 1 in L. Nakuru and 202 mg L 1 in L. Elmenteita. Using HPLC, the cyanobacterial hepatotoxins microcystin-LR, -RR -YR, -LF and -LA and the neurotoxin anatoxin-a were detected in phytoplankton samples from L. Bogoria and L. Nakuru. Total microcystin concentrations amounted to 155 g microcystin-LR equivalents g 1 DW in L. Bogoria, and 4593 g microcystin-LR equivalents g 1 DW in L. Nakuru, with anatoxin-a concentrations at 9 g g 1 DW in L. Bogoria and 223 g g 1 DW in L. Nakuru. In L. Elmenteita phytoplankton, no cyanobacterial toxins were found. A. fusiformis was identified as one source of the toxins. The isolated strain of A. fusiformis from L. Bogoria was found to produce both microcystin-YR (15.0 g g 1 DW) and anatoxin-a (10.4 g g 1 DW), whilst the A. fusiformis strain from L. Nakuru was found to produce anatoxin-a (0.14 g g 1 DW). Since A. fusiformis mass developments are characteristic of alkaline-saline lakes, health risks to wildlife, especially the Arthrospira-consuming Lesser Flamingo, may be expected.