Osmotic concentrations in the hemolymph and tissues are greater than in the surrounding water, resulting in water gain and ion loss. The large surface areas of the gills and mantle cavity compound this problem.
To maintain a constant osmotic state, mussels have very low hemolymph and cell osmotic concentrations (McMahon 1991). Active transport of ions across membranes maintains necessary osmotic concentrations within the mussel. Osmoregulation in zebra mussels has been comprehensively examined by Horohov et al. (1992) and Dietz et al. (1994, 1996, 1997).