The influence of the diel climatic cycle on the depth-time distribution of phytoplankton and photosynthesis in a shallow equatorial lake (Lake Baringo,Kenya)

Lake Baringo is a shallow equatorial lake. This paper reports a diel study of the depth-time distribution of phytoplankton and photosynthesis at one location in Lake Baringo on 10 March 1989. The water column shows a pattern of diurnal stratification probably accentuated by the high turbidity of the water and therefore rapid attenuation of solar energy. This stratified pattern breaks down at night due to atmospheric cooling and the regular onset of winds in the early evening. The phytoplankton is dominated byMicrocystis aeruginosa with some associated epiphytes. It concentrates in the narrow euphotic zone during the diurnal period of stratification due to buoyancy of theMicrocystis; evening breakdown of the thermocline results in the phytoplankton being mixed throughout the water column. A series of measurements of photosynthesis throughout the diurnal period gives an areal rate of 3.8 g O₂ m⁻² d⁻¹. The relationship between this value and the level of fish exploitation in Lake Baringo is discussed. The diel cycle in Lake Baringo is interpreted as dominating over any seasonal limnological cycle in the lake.     

FLUCTUATING ALGAL FOOD POPULATIONS AND THE OCCURRENCE OF LESSER FLAMINGOS (PHOENICONAIAS MINOR) IN THREE KENYAN RIFT VALLEY LAKES1

The last two decades have witnessed increasing episodes of lesser flamingo die‐offs in East Africa. Based on data on phytoplankton composition, biomass, and flamingo population density in three alkaline‐saline lakes of Kenya (Bogoria, Nakuru, and Oloidien) in 2001–2010, this study explored the link between sudden flamingo deaths and fluctuations in algal food quantity and quality. The phytoplankton biomass ranged from 13 to 768 mg · L^?1. Similarly, flamingo numbers varied widely from <1,000 to >500,000 individuals in the study lakes. The dominance of the cyanobacterium Arthrospira fusiformis (Woron.) Komárek et J. W. G. Lund was interrupted at irregular intervals in each lake and replaced partly by populations of different species of the nostocalean Anabaenopsis or by the picoplanktonic chlorophyte Picocystis salinarum Lewin. The populations of Anabaenopsis have the potential of blocking the flamingo food filtration system with their large and slimy colonies; moreover, they are able to produce cyanotoxins. Estimates of flamingo populations suggest that low flamingo numbers coincided with periods of low algal food quantity and/or poor quality. A food deficit can be theorized to have two effects on the flamingos: (i) it weakens them to the point of being susceptible to attacks of infective diseases, such as the ones caused by Mycobacterium avium and Pseudomonas aeruginosa, and (ii) it predisposes them to poisoning by cyanotoxins and pollutants, by reducing their capacity to handle toxic substances. This study therefore concludes that the challenges facing the flamingos are associated with changes in their environment, which affect food and water supply.     

Temporal changes in phytoplankton structure and composition at the Turkwel Gorge Reservoir,Kenya

Temporal changes in phytoplankton chlorophyll a, composition, diversity, biomass (density and fresh weight) and primary production were investigated at the Turkwel Gorge Reservoir (Kenya) over a two year period (1994 and 1995). The phytoplankton properties investigated revealed a seasonal pattern that was very distinct in 1994 and muted in 1995. The wet season was characterized by higher levels of chlorophyll a, biomass and primary production and a lower diversity. A prominent seasonality in 1994 was found to be the result of a higher river inflow volume as compared to 1995. Chlorophyll a changes showed some positive correlation to changes in total nitrogen and total phosphorus. Diversity changes were inversely correlated to changes in total counts (R = −0.84 and −0.96 for 1994 and 1995 respectively). Individual species density changes varied from a distinct seasonal pattern to a nearly uniform density. While the diatom Achnanthes dominated the wet season in 1994, coccoid blue green algae were dominant during most of 1995. Throughout the study period, most biomass was due to the diatoms but with a lower percentage of total biomass in 1995 (40%) as compared to 1994 (88%). The wet season biomass in each year was dominated by the diatoms. Dominance of the intervening period changed irregularly between diatoms, dinoflagellates, green algae and blue green algae. The range of variation in chlorophyll a, total biomass and primary production were; 4.9 to 36.8 μg l^-1, 440.14 to 11172.70 mg m^-3 and 1.85 to 9.67 g O₂ m^-2 d^-1 in 1994 and 4.9 to 11.5 μg l^-1, 486.46 to 1351.39 mg l^-1 and 3.08 to 5.41 g O₂ m^-2 d^-1 in 1995 in the same order. This revised version was published online in July 2006 with corrections to the Cover Date.     

Molecular detection of uncultured cyanobacteria and aminotransferase domains for cyanotoxin production in sediments of different Kenyan lakes

PCR-based denaturing gradient gel electrophoresis (DGGE) analysis of 16S rRNA gene fragments was used to identify the cyanobacterial phylotypes in sediments and plankton of saline–alkaline and freshwater lakes of Kenya. The detection of the aminotransferase domain located on modules mcyE and ndaF using specific molecular markers confirmed the presence of potential toxin-producing cyanobacteria. The eight nucleotide sequences obtained from DGGE bands were placed in three divergent cyanobacterial clusters. Five nucleotide sequences were close to members of the genera Anabaenopsis and Umezakia ( Nostocales ), two sequences fell in the cluster with Arthrospira sp. ( Oscillatoriales ) and one sequence was related to Chroococcidiopsis sp. ( Pleurocapsales ). The presence of the latter taxon was demonstrated de novo in the investigated lakes. All nine attained nucleotide sequences of the aminotransferase region belonged to the mcyE module. Five sequences of the aminotransferase domain were included in the cluster having the nucleotide sequence of Anabaena sp. but showed a separate lineage. Other four aminotransferases were placed in the cluster represented by nucleotide sequence of Microcystis aeruginosa . To our knowledge, this is the first report on molecular detection of cyanobacterial phylotypes in sediments of African lakes and aminotransferase domains for cyanotoxin production from sediment samples in general.     

Changes of phytoplankton communities in Lakes Naivasha and Oloidien, examples of degradation and salinization of lakes in the Kenyan Rift Valley

Increasing degradation of the water quality, caused by overuse and salinization, leads to considerable changes of the phytoplankton composition in Kenyan Rift Valley lakes. Exemplarily, the phytoplankton communities and biomasses of deteriorating freshwater Lake Naivasha and salinizing Lake Oloidien were studied between 2001 and 2005, accompanied by physico-chemical measurements (pH, total phosphorus and nitrogen, alkalinity, conductivity). Over the last three decades, the ecology of these two water basins has been subjected to dramatic changes, caused by excessive use of water and catchment area by man. In L. Naivasha a shift in the dominance of coccoid cyanobacteria towards dominance of Chlorophyceae (Botryococcus terribilis) was observed. Lake Oloidien exhibited a shift in the dominance of coccoid Chlorophyceae towards dominance of cyanobacteria (Arthrospira fusiformis, Anabaenopsis elenkinii). Phytoplankton findings and chemical data demonstrate that L. Naivasha has developed towards a eutrophic freshwater lake while L. Oloidien has progressed towards a hypereutrophic alkaline-saline lake. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users. Handling editor: J. Padisak     

Does the potentially toxic cyanobacterium <Emphasis Type="Italic">Microcystis</Emphasis> exist in the soda lakes of East Africa?

Presently, the food chains of the famous saline alkaline flamingo-lakes of East Africa are the focus of intense scientific discussion as the lakes host toxic cyanobacteria, which when consumed by Lesser Flamingos, weaken the birds and therefore make them susceptible to attacks by infective diseases. The distribution, genetic and toxicological aspects of Microcystis in Kenya has been studied extensively. Although there are reports on the occurrence of Microcystis in Kenya’s hypersaline alkaline lakes, they have not been confirmed. Our investigations carried out over a 10-year period in about 50 inland waters showed that Microcystis occurs exclusively in freshwaters, but never in the hypersaline alkaline lakes. Microscopic examinations of the phytoplankton of these lakes revealed the presence of Anabaenopsis abijatae (Nostococales) whose lumpy structure makes it roughly similar to Microcystis when viewed under an inverted microscope. We conclude that the possible occurrence of Microcystis in hypersaline alkaline lakes is doubtful and, as such, confirmatory studies including microphotographic documentation of findings should be carried out.     

Cyanobacteria and cyanobacterial toxins in the alkaline crater lakes Sonachi and Simbi, Kenya

The phytoplankton communities and the production of cyanobacterial toxins were investigated in two alkaline Kenyan crater lakes, Lake Sonachi and Lake Simbi. Lake Sonachi was mainly dominated by the cyanobacterium Arthrospira fusiformis, Lake Simbi by A. fusiformis and Anabaenopsis abijatae. The phytoplankton biomasses measured were high, reaching up to 3159 mg l⁻¹ in L. Sonachi and up to 348 mg l⁻¹ in L. Simbi. Using HPLC techniques, one structural variant of the hepatotoxin microcystin (microcystin-RR) was found in L. Sonachi and four variants (microcystin-LR, -RR, -LA and -YR) were identified in L. Simbi. The neurotoxin anatoxin-a was found in both lakes. To our knowledge this is the first evidence of cyanobacterial toxins in L. Sonachi and L. Simbi. Total microcystin concentrations varied from 1.6 to 12.0 μg microcystin-LR equivalents g⁻¹ DW in L. Sonachi and from 19.7 to 39.0 μg microcystin-LR equivalents g⁻¹ DW in L. Simbi. Anatoxin-a concentrations ranged from 0.5 to 2.0 μg g⁻¹ DW in L. Sonachi and from 0 to 1.4 μg g⁻¹ DW in L. Simbi. In a monocyanobacterial strain of A. fusiformis, isolated from L. Sonachi, microcystin-YR and anatoxin-a were produced. The concentrations found were 2.2 μg microcystin g⁻¹ DW and 0.3 μg anatoxin-a g⁻¹ DW. This is the first study showing A. fusiformis as producer of microcystins and anatoxin-a. Since A. fusiformis occurs in mass developments in both lakes, a health risk for wildlife can be expected.     

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

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.