Use it or lose it : Factors affecting the fitness and dominance shifts of dreissenid mussels

The bivalves Dreissena polymorpha or zebra mussel (Pallas 1771) and D. bugensis or quagga mussel (Andrusov 1897) originate from river estuaries north of the Ponto-Caspian basins. They spread out of their native area along rivers, attached to boat hulls and in ballast water invading hard freshwater surfaces in large parts of the northern hemisphere (Leuven et al. 2009). Both in their native and introduced areas ongoing dominance shifts are observed going from the first introduced D. polymorpha to D. bugensis as the dominant species (Karatayev et al. 2011, Matthews et al. 2014, D’Hont et al. 2018). However, the drivers of these dominance shifts are still largely unknown. During the present study, we tried to identify species traits and external factors leading to higher fitness and competitive benefits for either one of these species.