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Langzeituntersuchungen (1969-2002) zur verbreitung der cladoceren auf den niedersächsischen sandinseln der sudlichen Nordsee, Deutschland

Hollwedel W.

Studia Quaternaria

2004

Vol. 21

25-36

From 1969 to 2002 the distribution of cladoceran species on ten islands in the southern North Sea was investigated. A total of 50 species was found. The small water bodies in the salt marsh have to be resettled after salt water floods; Macrothrix hirsuticornis and Moina brachiata are two of the pioneer species in the brackish water bodies. Most cladoceran species were found in permanent and temporary dune waters. Some of them were caught only occasionally and in low abundance. A characteristic species of dune waters is Scapholeberis rammneri, which was detected on eight islands. A small group of cladoceran species inhabited concrete basins containing drinking water for cattle and horses. The Hammersee on Juist island, a shallow freshwater lake since a dyke had been built in 1928, was inhabited by 35 species. Within the last decade the species number decreased because of eutrophication and biotopes being filled up by sedimentation. On islands with newly dug water bodies species number increased. The two species, Macrothrix hirsuticornis and Scapholeberis rammneri, characteristic of the islands in the southern North Sea, are endangered due to changes and losses of habitats on all but one (Wangerooge) islands.