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Abstract

In natural habitats Daphnia magna and Daphnia pulex have different ranges of extension with respect to pH-conditions in ponds. In acid brooks Gammarus pulex will survive longer than Gammarus fossarum . Investigations in the laboratory showed that, correspondingly, D. magna is more sensitive to low pH than D. pulex , and G. fossarum more sensitive than G. pulex . Mortality increased in close relation to increasing acidity and is mainly caused by the increasing concentration of free hydrogen ions. Anions are less important, which was shown in experiments with five different acids, including acid drip water from a fir forest. Low pH-values may lead to the mobilization of heavy metalions, which can increase the toxicity of a medium. Under experimental conditions crustaceans can improve pH-values when they release ammonia and amino-acids. The limnological importance of this behaviour is briefly discussed.