title: Species-specific separation of lake plankton reveals divergent food assimilation patterns in rotifers.
abstract: 1. The analysis of functional groups with a resolution to the individual species level is a basic requirement to better understand complex interactions in aquatic food webs. Species-specific stable isotope analyses are currently applied to analyse the trophic role of large zooplankton or fish species, but technical constraints complicate their application to smaller-sized plankton. 2. We investigated rotifer food assimilation during a short-term microzooplankton bloom in the East African soda lake Nakuru by developing a method for species-specific sampling of rotifers. 3. The two dominant rotifers,Brachionus plicatilisandBrachionus dimidiatus, were separated to single-species samples (purity >95%) and significantly differed in their isotopic values (4.1‰ in δ13C and 1.5‰ in δ15N). Bayesian mixing models indicated that isotopic differences were caused by different assimilation of filamentous cyanobacteria and particles <2 μm and underlined the importance of species-specific sampling of smaller plankton compartments. 4. A main difference was that the filamentous cyanobacteriumArthrospira fusiformis, which frequently forms blooms in African soda lakes, was an important food source for the larger-sizedB. plicatilis(48%), whereas it was hardly ingested byB. dimidiatus. Overall,A.fusiformiswas, relative to its biomass, assimilated to small extents, demonstrating a high grazing resistance of this species. 5. In combination with high population densities, these results demonstrate a strong potential of rotifer blooms to shape phytoplankton communities and are the firstin situdemonstration of a quantitatively important direct trophic link between rotifers and filamentous cyanobacteria.
authors: Department of Ecology, Environment and Plant Sciences, Stockholm University Stockholm, Sweden.
authors: Alfred
authors: A
authors: Burian
authors: WasserCluster Lunz - Inter-university Centre for Aquatic Ecosystem Research Lunz am See, Austria.
authors: Martin J
authors: MJ
authors: Kainz
authors: Department of Limnology, University of Vienna Vienna, Austria.
authors: Michael
authors: M
authors: Schagerl
authors: Biological Department, Egerton University Njoro, Kenya.
authors: Andrew
authors: A
authors: Yasindi
keywords: Brachionus plicatilis; Lake Nakuru; cyanobacteria; dietary sources; size fractionation; stable isotopes; zooplankton