Population dynamics of Melanoides tuberculata (Müller) (Gastropoda: Prosobranchia: Thiaridae) near a cooling water discharge in the Twenthe Canal (The Netherlands)

The occurrence of the (sub-)tropical freshwater snail Melanoides tuberculata (Müller) in a canal in the eastern part of The Netherlands was monitored during the period August 1992-September 1993. The species lives in a cooling water discharge plume which appears to be a good refugium for this thermophile organism. After winter, density had decreased considerably; however, the species did not become extinct. From shell length/frequency distributions, two to three cohorts could be distinguished, depending on the sampling period.