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Abstract

Abstract On the East Frisian Island of Spiekeroog the effect of the hurricane-flood in 1962 has shown that Cladocera populations can be destroyed only when they are surprised in an active phase by seawater. Resting-eggs are resistant to high salt-contents. Higher salt-contents force resting-eggs to continue resting until the pond water has become fresh again. Breeding-experiments have proved that dune-ponds have stable biocoenoses while salt-marsh ponds are shown to be biotopes which are not saturated. This explains why the species maximum is to be found within those island areas threatened by storm-floods. Four of the six Cladocera living on Spiekeroog are important laboratory species.