Molecular diversity of plankton in a tropical crater lake switching from hyposaline to subsaline conditions: Lake Oloidien, Kenya

Salinity in the climate sensitive tropical endorheic crater lake Oloidien (Great African Rift Valley, Kenya) decreased from hyposaline to subsaline conditions during the period 2010-2015. The change in salinity was accompanied by a pronounced change in planktonic life forms-from blooms of the cyanobacterium Arthrospira supporting tens of thousands of Lesser Flamingos to highly diverse communities of cyanobacteria and algae which do not sustain the consumer birds. Besides the well-known macro- and microscopic lake life, a hidden diversity of microorganisms was detected using molecular methods. SSU rRNA gene clone libraries and data from Ilumina Miseq sequencing of samples collected at the two contrasting stages revealed distinct and highly diverse microbial communities. Different bacterial clades dominated the two samples. In 2011, Firmicutes (class Bacilli) whose origin was the fecal waste of birds were the dominant group. However, the Cyanobacteria and Chloroflexi were the most prevalent in 2015. From the microbial eukaryote samples obtained in 2011, rotifers and ciliates that feed on Arthrospira and rich bacterial food dominated the plankton, while the cryptophytes were the most prevalent in 2015. On the two occasions, a mixture of organisms previously not known to occur in saline or in freshwater habitats was found.