LEPTODORA-KINDTI - EFFICIENT PREDATOR AND PREFERRED PREY ITEM IN NEUSIEDLER-SEE, AUSTRIA

In the Neusiedler See, Leptodora kindti appeared in the plankton in April/May; the growing season lasted until November. Its optimum conditions prevailed during the summer months, when densities of >500 ind, m(-3) were recorded. First, males appeared by the mid/end of August, while maximum resting egg production occurred in September. At temperatures below 10 degrees C the population declined. At high population levels, L, kindti caused suppression of its preferred prey item, the juveniles of Diaphanosoma mongolianum. Twenty-five to 45% of juvenile Diaphanosoma can be eliminated by Leptodora. This predation impact is a pronounced but short-term event. During the periods of high Leptodora densities, a significant relationship between Leptodora predation and the death rate of Diaphanosoma is found. The older developmental instars of L. kindti are themselves endangered by the impact of planktivorous fish (i.e. Pelecus cultratus, Alburnus alburnus), which show a preference for Leptodora larger than 6 mm. Frequently, elimination by fish corresponds with high death rates of Leptodora. During the periods when adult Leptodora occurred in numbers >50 ind. m(-3), 55% of the variance connected with its death rate can be attributed to fish predation. The success of this population of L. kindti is discussed within the framework of predator-prey interactions.