Groei maar geen voortplanting van Quaggamossels in een geïsoleerde zandwinplas

Growth and reproduction of the Zebra mussel Dreissena polymorpha (Pallas, 1771) and Quagga mussel Dreissena bugensis (Andrusov, 1897) were studied in an isolated sandpit near Lelystad, province of Flevoland. Apart from possible introduction of dreissenids by water birds, introduction of zebra mussels could have taken place in 1977 during sand extraction or in the eighties during an experimental study of the feeding strategy of diving ducks. Quagga mussels were certainly introduced in 2008 when caged mussels were stored in the sandpit for some weeks before they were used for a growth study elsewhere. In 2016 two adult Quagga mussels were found that perhaps derived from this introduction. Although from that time the Dreissena community in the sandpit was monitored regularly, no more Quagga mussels were encountered. To check whether growth inhibition could be the reason for their absence, growth of caged Zebra and Quagga mussels with an initial shell length of 6, 7 or 8 mm was monthly monitored in 2020 (and only for Quagga mussels continued and repeated in 2021). Both species grew well, comparable with their growth as recorded in the IJsselmeer lake in 2012. Remarkable was the linear growth of the Quagga mussels between October 2020 and December 2021. It was concluded that shortage of food could not be the reason for the absence of Quagga mussels from the sandpit.