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[Valve movement of the mussel Dreissena polymorpha as a monitoring system for bodies of water].

A new biological "early warning system" for continuous water control is presented that is based on the valve movements of the freshwater mussel Dreissena polymorpha. For two groups of up to 42 mussels, both the percentage of open mussels and the number of valve movements during a time interval are used to describe the activity behaviour of the zebra mussel. A main prerequisite of such a biomonitor should be the knowledge of the "normal" behaviour in correlation to changing environmental conditions. Preliminary results in Dreissena demonstrate the influence of the temperature, the daily cycle of light and the food concentration on both characteristics of the activity pattern. During toxicity tests, the mussels reacted significantly within 3-30 minutes after the addition of a toxicant. This was normally observed by both the decrease of the percentage of open mussels and the increase of the number of valve movements. Therefore--and against the background of the well-known "normal" behaviour--reliable limits for the detection of a harassing event can be defined. First experiments with Pentachlorophenol, Lindane, Atrazine and 2-Nitrophenol demonstrated to some extent a higher sensitivity compared to other "early warning systems".