Die pelagischen Rotatorien des Sempachersees,mit spezieller Berücksichtigung der Brachioniden und der Ernährungsfrage

The pelagic Rotifers of the mesotrophic lake of Sempach (Switzerland) were investigated qualitatively and quantitatively from 1969 to 1971. The Rotifer reproduction rate was highest from spring until early summer, with peaks of 0.86 million individuals below 1 dm² in 1969, and 0.92 in 1970. During summer stratification, production was comparatively low. During both yearsKeratella cochlearis made up on an average of 50% of the total number of Rotifers.Keratella cochlearis, K. quadrata andKellicottia longispina reproductive rates were calculated, using the egg ratio method of Edmondson. The highest yearly rates of the three species were noted in spring at a depth of 0 to 5 m. From spring until early summer in 1970, 88% of the biomass of the first large phytoplankton peak were nannoplankton, 70% of which consisted of Cryptophycease and Chrysophyceae from the end of April until the middle of June. During the investigation of the three Brachionidae, inquiries into the food relation of nannoplankton algae showed close relations to these algae groups and more over to μ-algae. In spring the ChrysophyceaeErkenia subaequiciliata seems to be the most important food for the three Rotifer species.