Distribution and competitive impact of the exotic Chinese mystery snail in the James River, Southwest Missouri

The exotic Chinese mystery snail (Bellamya chinensis, CMS) is a large viviparid capable of inhabiting both lakes and streams.  Following a discovery of a population in the Missouri Ozarks in 2007, we surveyed 27 depositional areas in the lower James River the following year.  Two of 27 sites were positive for CMS, and densities were generally low (0.05 m^-2).  We collected nine adult CMS as brood stock for laboratory cultures, removed newborn offspring, and marked 54 individuals for growth rates.  The adult CMS produced 10.5 offspring snail^-1 month^-1.  Over a two month period the juveniles increased their shell length by 0.1 mm day^-1.  A food preference study with CMS and the native pulmonate Physa gyrina indicated a broad overlap in diet, with both species preferring periphyton-encrusted rocks.  A resource competition experiment between juvenile P. gyrina (four individuals per 500 mL jar) and CMS used an additive design (0, 1, 2, 3, 4 CMS per jar).  Decreased growth rates of P. gyrina with increasing CMS densities were consistent with effects of competition (R² = 40%, p < 0.001).  Lakes or streams with high densities of exotic CMS could see a reduction in native snails through competitive exclusion.