Ciliated protozoa in Lake Nakuru, a shallow alkaline-saline lake in Kenya: Seasonal variation, potential production and role in the food web

Abstract

Six sampling sites in Lake Nakuru were sampled monthly for 8 months spanning rainy and dry seasons, and including an interval when Spirulina-dominated the phytoplankton community. A total of 33 species in 29 genera were observed. Small bacterivorous ciliates, especially Cyclidium, were numerically dominant, but the greatest biomass was due to the large ciliate Condylostoma. Abundance ranged from 10.4 to 14,200 ciliates mL -1 (mean ± SE = 1,150 ± 309 ciliates mL -1 ) while biomass ranged from 0.017 to 500 mg C.L -1 (mean 18.2 ± 10.8 mg C.L -1 ). Ciliates were generally large (mean equivalent spherical diameter 43 μm) compared to previous studies of marine or freshwater plankton. Using published maximum growth rates for the species, we calculated that ciliate production could be as much as 6.4 ± 2.3 mg C L -1 , which is higher than previous estimates of primary production, and indicates that ciliates probably play a major role in energy flow in this system. Most of the estimated production was by large ciliates, the algivorous Frontonia (58 %) and the predacious Condylostoma (33 %), while the more numerous bacterivores contributed only 4%.