Quantitative Untersuchungen zur Ökologie der Gastrotrichen in Gezeiten-Sandstrand der Insel Sylt

Quantitative investigations were made on the distribution of 21 species of Gastrotricha Macrodasyoidea and 2 species of Chaetonotoidea in 10 different tidal beach areas of the island Sylt (North Sea). Most species live in the upper few centimeters of sandy flats near the low tide level. We counted up to 989 Gastrotricha in 50 cm³ of sediment. This group comprises up to 24% of the total interstitial fauna in about 25 samples. The beach slopes are inhabited by different species which are much less abundant (up to 165 animals per 50 cm³ sediment, and up to 7% of the total interstitial fauna). Each species inhabits a distinct zone of the sand flat or the beach slope. These zones run parallel to the water line and follow one another in a characteristic succession from the sublittoral to the supralittoral. It is assumed that several factors, controlled by exposure — e.g. variations of temperature and salinity as well as oxygen avilability — are responsible for the distribution patterns observed.