Dreissena polymorpha Pallas, 1771

Unionids with zebra mussels attached to their shells can have difficulty burrowing and moving through sediment, or the extra weight can result in burial in very soft sediments. Attached mussels can prevent unionids from opening their valves for respiration, feeding and reproduction, or can prevent closing valves as well. (Karatayev et al. 2007) Fouled mussels had a lower physiological condition than unfouled mussels. Unlike tissue mass : shell mass ratio, tissue glycogen content was independent of mussel size, making it a particularly useful measure of condition (Sousa et al. 2011)

The effects of invasion can be local, mostly affecting the benthos, especially those areas where mussels settle, or system-wide, where the invasion influences large areas or entire water bodies through both direct and indirect effects of the mussels on physical, chemical, and biological properties of the environment.

The effects of invasion can be local, mostly affecting the benthos, especially those areas where mussels settle, or system-wide, where the invasion influences large areas or entire water bodies through both direct and indirect effects of the mussels on physical, chemical, and biological properties of the environment.

Commonly observed changes include reductions in phytoplankton and zooplankton (MacIsaac, Lonnee & Leach, 1995; Caraco et al., 1997; Pace, Findlay & Fischer, 1998; Strayer et al., 2008) (Sousa et al. 2011)

Although European unionids appear to be less sensitive to D. polymorpha than American ones (Karatayev, Burlakova, & Padilla, 1997), their strong declines or local extinctions following the invasion of D. polymorpha have been recorded (Aldridge et al., 2004; Arter, 1989; Lewandowski, 1991; Lucy, Burlakova, Karatayev, Mastitsky, & Zanatta, 2014) (Ozgo et al. 2020)

Although European unionids appear to be less sensitive to D. polymorpha than American ones (Karatayev, Burlakova, & Padilla, 1997), their strong declines or local extinctions following the invasion of D. polymorpha have been recorded (Aldridge et al., 2004; Arter, 1989; Lewandowski, 1991; Lucy, Burlakova, Karatayev, Mastitsky, & Zanatta, 2014) (Ozgo et al. 2020) The decline of unionoid mussels following the introduction of zebra mussels has been well documented in North America, with near total extinction within a few years after invasion in several lakes (e.g. Lake St. Clair and Lake Erie) and rivers (e.g. St. Lawrence River) with very high fouling intensities (Gillis & Mackie, 1994; Nalepa, 1994; Schloesser & Nalepa, 1994; Ricciardi, Whoriskey & Rasmussen, 1996; Martel et al., 2001) (Sousa et al. 2011)

However, Strayer & Malcom (2007) also showed that, after initial declines, unionoid populations in Hudson River have stabilised or even recovered, with the initial declines in population sizes and body condition correlated with the filtration rates of zebra mussels but not with fouling.