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Langzeituntersuchungen (1969–2002) zur Verbreitung der Cladoceren auf den Niedersächsischen Sandinseln der südlichen Nordsee, Deutschland

Long-term studies (1969–2002) of the cladoceran distribution on the sandy islands of the sourthern North Sea in Lower Saxony, Germany

Werner Hollwedel

 Abstract

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 numbers increased.