The trophic position of planktonic ciliate populations in the food webs of some East African lakes

Evidence supporting the importance of nutrient regeneration by nano- and micrograzers for phytoplankton photosynthesis in Lake Malawi/Nyasa

“…Both wet and dry stratified seasons had relatively similar stoichiometric ratios indicative of moderate N and P deficiency while the metabolic measures of N and P debt were indicative of N and P deficient phytoplankton. The size fractionated incubations conducted in this study demonstrate the probable importance of nutrient regeneration by ciliates (Yasindi and Taylor, 2006;Yasindi et al, 2007) and heterotrophic nanoflagellates during the strongly stratified dry season to the nutrient status of the phytoplankton. Unfortunately our interpretation is based solely upon the physiological responses of picoplankton isolated from nano and micrograzers and not on actual grazing and nutrient regeneration rates by nano and micrograzers.…”

“…The microbial food web does appear to be responsible for maintaining the relatively low variability in chlorophyll in the whole water and also keeping the stoichiometry of the particulate matter indicative of only moderate nutrient stress. The capacity of micrograzers for high growth rates (Yasindi and Taylor, 2006) comparable to the pico-and nanophytoplankton gives them the capacity to respond to increased growth rates by the pico-and nanophytoplankton and quickly limit any biomass increase by them, especially under generally low nutrient conditions (Callieri and Stockner, 2002). However, a large portion of the consumed nutrient will be regenerated for uptake by the picophytoplankton.…”

Food Webs

“…Eutrophic waters have the conditions to sustain high productivity rates of phototrophs and heterotrophic bacteria, sustaining, in turn, large populations of their grazers, promoting the increase of predatory ciliate population [69]. Biomass of raptor ciliates may reach almost an order of magnitude higher in eutrophic compared to the one obtained in meso and oligotrophic lakes, suggesting that they are effectively controlling the primary productivity [70]. This assumption is supported by the covariance of predatory ciliates and their preferred food.…”

Elemental ratios (C:N) and stable isotopic composition of dominant rotifer species in a tropical eutrophic alkaline–saline Lake Nakuru (Kenya)

“…Vareschi, 1982;Vareschi & Vareschi, 1984;Vareschi & Jacobs, 1985;Finlay et al, 1987;Gilabert, 2001;Yasindi et al 2007;Oyoo-Okoth et al, 2011;Ong'ondo et al, 2013). Generally rotifers thrive well under eutrophic conditions, for example, they may reach population densities as high as 20,000 ind l -1 (Gulati et al, 1992;Ooms-Wilms et al, 1999;Bonecker & Aoyagui, 2005).…”