Mohr, S. Institut fuer Gewaesseroekologie und Binnenfischerei, mohr@igb-berlin.de
Adrian, R. Institut fuer Gewaesseroekologie und Binnenfischerei, adrian@igb-berlin.de

 
SIZE-SELECTIVE GRAZING OF TWO ROTIFER SPECIES ON A MANIPULATED FRESHWATER CILIATE COMMUNITY
 
Former laboratory investigations showed that the closely related rotifers Brachionus calyciflorus and Brachionus rubens differ in their food size preferences. B. calyciflorus feeds more efficiently on larger food items than B. rubens. This was confirmed in own laboratory grazing experiments with the ciliate Coleps spp. (length about 40 µm) where only B. calyciflorus was able to ingest this ciliate. In an in situ grazing experiment Coleps was added to the microplankton community of the Müggelsee (North-east Germany) in order to test the different feeding preferences of the two brachionids under natural food conditions. B. calyciflorus had a strong negative predatory impact on Coleps spp. and autotrophic flagellates, while the total number of ciliates, heterotrophic nanoflagellates and bacteria were only slightly or not affected. On the other hand B. rubens did not feed on Coleps but on ciliates of smaller size range (10-20 µm). B. rubens fed mainly on autotrophic flagellates and eliminated the size class of 5-10 µm completely. The results demonstrate that both rotifer species had a strong predatory impact on the microplankton community of the Müggelsee. However, given the differences in their food size spectrum, the impact on the microplankton community structure varies considerably.
 
Day: Wednesday, Feb. 3
Time: Poster
Location: Sweeney Center
 
Code: CS60WE0227S