Kurmayer, R. R. University of Vienna, Institute of Plant Physiology, Department Hydrobotany, kurmayer@pflaphy.pph.univie.ac.at
Jüttner, F. F. University of Zürich, Institute of Plant Biology, Limnological Station,

 
STRATEGIES FOR THE COEXISTENCE OF ZOOPLANKTON AND THE TOXIC CYANOBACTERIUM PLANKTOTHRIX RUBESCENS IN LAKE ZÜRICH, SWITZERLAND
 
Since the cyanobacterium Planktothrix rubescens contains several potent hepatotoxins and dominates the phytoplankton community in Lake Zürich, we addressed the question wether co-occurring zooplankton species have developed adaptive feeding responses. High sensitivity to microcystins of Planktothrix was coupled to strict food avoidance in Eudiaptomus gracilis. Daphnia hyalina and Cyclops abyssorum exhibited higher physiological resistance to microcystins and ingested Planktothrix. Neither the feeding of copepods nor the feeding of Daphnia on high-quality algae was significantly reduced in the presence of Planktothrix. Feeding rates of Daphnia on Planktothrix doubled after microcystins have been extracted indicating that microcystins are important feeding deterrents against the grazing pressure of Daphnia. On the other hand, copepods persisted in food avoidance even after the extraction of the major part of microcystins. It is concluded that unknown, probably less toxic compounds may be responsible for the behaviour of food avoidance of copepods and the grazing resistance of Planktothrix is mediated by chemical defense rather than by the large size and the rigidity of the filaments.
 
Day: Thursday, Feb. 4
Time: 11:30 - 11:45am
Location: Hilton of Santa Fe
 
Code: SS16TH1130H