Staan we aan een begin van de rekolonisatie van het IJsselmeer door de zoetwaterneriet Theodoxus fluviatilis?

By the end of the past century the freshwater nerite Theodoxus fluviatilis (Linnaeus, 1758) disappeared from Lake IJsselmeer. However, recently a relatively large number of specimens were found in Dreissena samples from the Enkhuizerzand, a former sandbank from the time the area was part of the Zuiderzee. The data of August 2009 show two cohorts in the population with a shell width of 1-3 and 4-7 mm, respectively, suggesting growth and reproductionin the area. Since T . fluviatilis is a scraper of sessile algae, the recolonization of the 2.5-4 m deep Enkhuizerzand indicates improvement of the trophic status of the lake which makes sessile algal growth at these depths possible.