Short term colonization and subsequent extinction of a population of Lithoglyphus naticoides (Pfeiffer) (Gastropoda, Prosobranchia, Hydrobiidae) in the IJsselmeer, the Netherlands

The freshwater snail Lithoglyphus naticoides (Pfeiffer) was found in bottom samples from an area in the southern part of the lake IJsselmeer in 1984. From August 1984 to November 1985 a permanent site was sampled with monthly intervals as far as possible. Average density increased from 35 specimens per m² in August 1984 to 95 in December 1984. However, at the end of 1985 density had reached the limit of detection. In 1984 and 1985, two generations could be distinguished. After the growth period average shell sizes of both generations were approximately 2.5 and 5-6 mm respectively. A new generation could be expected in the population from the second part of June onwards. Possibilities of subsequent extinction are discussed.