Are there differences in the fouling of the native and invasive Unionidae by Dreissena polymorpha?

Bivalves of the family Unionidae live partly buried in the sediments, usually with the posterior part of their shell exposed to the water column to enable filtration. This exposed part of the shell can therefore serve as a substratum for zebra mussels (Dreissena polymorpha), which limit the host’s ability to feed, move, and breed. We analyzed images of shells of 2 unionid species from Lake Gosławskie in western Poland: the native duck mussel (Anodonta anatina) and the invasive Chinese pond mussel (Sinanodonta woodiana). Our results show that these 2 species significantly differed in shell surface available to zebra mussels. A. anatina was consistently more heavily fouled than S. woodiana and had a greater surface area of the shell exposed in the water column. On average, only 25.5% of the shell of S. woodiana was exposed above the sediments (range 17.6–39.2%) compared to 45.4% of the shell of A. anatina (range 24.6–64.4%). Thus S. woodiana is more deeply buried in the mud, providing better protection from the negative impact of zebra mussels and making this Chinese species more competitive than the native A. anatina.